[PATCH kernel v2 0/2] KVM: PPC: Check if IOMMU page is contained in the pinned physical page

This is to improve page boundaries checking and should probably
be cc:stable. I came accross this while debugging nvlink2 passthrough
but the lack of checking might be exploited by the existing userspace.

Changes:
v2:
* 2/2: explicitly check for compound pages before calling compound_order()


Please comment. Thanks.



Alexey Kardashevskiy (2):
  vfio/spapr: Use IOMMU pageshift rather than pagesize
  KVM: PPC: Check if IOMMU page is contained in the pinned physical page

 arch/powerpc/include/asm/mmu_context.h |  4 ++--
 arch/powerpc/kvm/book3s_64_vio.c       |  2 +-
 arch/powerpc/kvm/book3s_64_vio_hv.c    |  6 ++++--
 arch/powerpc/mm/mmu_context_iommu.c    | 20 +++++++++++++++++---
 drivers/vfio/vfio_iommu_spapr_tce.c    | 10 +++++-----
 5 files changed, 29 insertions(+), 13 deletions(-)

-- 
2.11.0

The size is always equal to 1 page so let's use this. Later on this will
be used for other checks which use page shifts to check the granularity
of access.

This should cause no behavioral change.

Reviewed-by: David Gibson <redacted>
Signed-off-by: Alexey Kardashevskiy <redacted>
---
 drivers/vfio/vfio_iommu_spapr_tce.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
index 759a5bd..2da5f05 100644
--- a/drivers/vfio/vfio_iommu_spapr_tce.c
+++ b/drivers/vfio/vfio_iommu_spapr_tce.c

@@ -457,13 +457,13 @@ static void tce_iommu_unuse_page(struct tce_container *container,
 }
 
 static int tce_iommu_prereg_ua_to_hpa(struct tce_container *container,
-		unsigned long tce, unsigned long size,
+		unsigned long tce, unsigned long shift,
 		unsigned long *phpa, struct mm_iommu_table_group_mem_t **pmem)
 {
 	long ret = 0;
 	struct mm_iommu_table_group_mem_t *mem;
 
-	mem = mm_iommu_lookup(container->mm, tce, size);
+	mem = mm_iommu_lookup(container->mm, tce, 1ULL << shift);
 	if (!mem)
 		return -EINVAL;
 

@@ -487,7 +487,7 @@ static void tce_iommu_unuse_page_v2(struct tce_container *container,
 	if (!pua)
 		return;
 
-	ret = tce_iommu_prereg_ua_to_hpa(container, *pua, IOMMU_PAGE_SIZE(tbl),
+	ret = tce_iommu_prereg_ua_to_hpa(container, *pua, tbl->it_page_shift,
 			&hpa, &mem);
 	if (ret)
 		pr_debug("%s: tce %lx at #%lx was not cached, ret=%d\n",

@@ -611,7 +611,7 @@ static long tce_iommu_build_v2(struct tce_container *container,
 				entry + i);
 
 		ret = tce_iommu_prereg_ua_to_hpa(container,
-				tce, IOMMU_PAGE_SIZE(tbl), &hpa, &mem);
+				tce, tbl->it_page_shift, &hpa, &mem);
 		if (ret)
 			break;
 

-- 
2.11.0

We already have a check in drivers/vfio/vfio_iommu_spapr_tce.c that
an IOMMU page is contained in the physical page so the PCI hardware won't
get access to unassigned host memory.

However we do not have this check in KVM fastpath (H_PUT_TCE accelerated
code) so the user space can pin memory backed with 64k pages and create
a hardware TCE table with a bigger page size. We were lucky so far and
did not hit this yet as the very first time the mapping happens
we do not have tbl::it_userspace allocated yet and fall back to
the userspace which in turn calls VFIO IOMMU driver and that fails
because of the check in vfio_iommu_spapr_tce.c which is really
sustainable solution.

This stores the smallest preregistered page size in the preregistered
region descriptor and changes the mm_iommu_xxx API to check this against
the IOMMU page size.

Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v2:
* explicitly check for compound pages before calling compound_order()

---
The bug is: run QEMU _without_ hugepages (no -mempath) and tell it to
advertise 16MB pages to the guest; a typical pseries guest will use 16MB
for IOMMU pages without checking the mmu pagesize and this will fail
at https://git.qemu.org/?p=qemu.git;a=blob;f=hw/vfio/common.c;h=fb396cf00ac40eb35967a04c9cc798ca896eed57;hb=refs/heads/master#l256

With the change, mapping will fail in KVM and the guest will print:

mlx5_core 0000:00:00.0: ibm,create-pe-dma-window(2027) 0 8000000 20000000 18 1f returned 0 (liobn = 0x80000001 starting addr = 8000000 0)
mlx5_core 0000:00:00.0: created tce table LIOBN 0x80000001 for /pci@800000020000000/ethernet@0
mlx5_core 0000:00:00.0: failed to map direct window for /pci@800000020000000/ethernet@0: -1
---
 arch/powerpc/include/asm/mmu_context.h |  4 ++--
 arch/powerpc/kvm/book3s_64_vio.c       |  2 +-
 arch/powerpc/kvm/book3s_64_vio_hv.c    |  6 ++++--
 arch/powerpc/mm/mmu_context_iommu.c    | 20 +++++++++++++++++---
 drivers/vfio/vfio_iommu_spapr_tce.c    |  2 +-
 5 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
index 896efa5..79d570c 100644
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h

@@ -35,9 +35,9 @@ extern struct mm_iommu_table_group_mem_t *mm_iommu_lookup_rm(
 extern struct mm_iommu_table_group_mem_t *mm_iommu_find(struct mm_struct *mm,
 		unsigned long ua, unsigned long entries);
 extern long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
-		unsigned long ua, unsigned long *hpa);
+		unsigned long ua, unsigned int pageshift, unsigned long *hpa);
 extern long mm_iommu_ua_to_hpa_rm(struct mm_iommu_table_group_mem_t *mem,
-		unsigned long ua, unsigned long *hpa);
+		unsigned long ua, unsigned int pageshift, unsigned long *hpa);
 extern long mm_iommu_mapped_inc(struct mm_iommu_table_group_mem_t *mem);
 extern void mm_iommu_mapped_dec(struct mm_iommu_table_group_mem_t *mem);
 #endif

diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
index d066e37..8c456fa 100644
--- a/arch/powerpc/kvm/book3s_64_vio.c
+++ b/arch/powerpc/kvm/book3s_64_vio.c

@@ -449,7 +449,7 @@ long kvmppc_tce_iommu_do_map(struct kvm *kvm, struct iommu_table *tbl,
 		/* This only handles v2 IOMMU type, v1 is handled via ioctl() */
 		return H_TOO_HARD;
 
-	if (WARN_ON_ONCE(mm_iommu_ua_to_hpa(mem, ua, &hpa)))
+	if (WARN_ON_ONCE(mm_iommu_ua_to_hpa(mem, ua, tbl->it_page_shift, &hpa)))
 		return H_HARDWARE;
 
 	if (mm_iommu_mapped_inc(mem))

diff --git a/arch/powerpc/kvm/book3s_64_vio_hv.c b/arch/powerpc/kvm/book3s_64_vio_hv.c
index 925fc31..5b298f5 100644
--- a/arch/powerpc/kvm/book3s_64_vio_hv.c
+++ b/arch/powerpc/kvm/book3s_64_vio_hv.c

@@ -279,7 +279,8 @@ static long kvmppc_rm_tce_iommu_do_map(struct kvm *kvm, struct iommu_table *tbl,
 	if (!mem)
 		return H_TOO_HARD;
 
-	if (WARN_ON_ONCE_RM(mm_iommu_ua_to_hpa_rm(mem, ua, &hpa)))
+	if (WARN_ON_ONCE_RM(mm_iommu_ua_to_hpa_rm(mem, ua, tbl->it_page_shift,
+			&hpa)))
 		return H_HARDWARE;
 
 	pua = (void *) vmalloc_to_phys(pua);

@@ -469,7 +470,8 @@ long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
 
 		mem = mm_iommu_lookup_rm(vcpu->kvm->mm, ua, IOMMU_PAGE_SIZE_4K);
 		if (mem)
-			prereg = mm_iommu_ua_to_hpa_rm(mem, ua, &tces) == 0;
+			prereg = mm_iommu_ua_to_hpa_rm(mem, ua,
+					IOMMU_PAGE_SHIFT_4K, &tces) == 0;
 	}
 
 	if (!prereg) {

diff --git a/arch/powerpc/mm/mmu_context_iommu.c b/arch/powerpc/mm/mmu_context_iommu.c
index abb4364..dc0e8cd 100644
--- a/arch/powerpc/mm/mmu_context_iommu.c
+++ b/arch/powerpc/mm/mmu_context_iommu.c

@@ -27,6 +27,7 @@ struct mm_iommu_table_group_mem_t {
 	struct rcu_head rcu;
 	unsigned long used;
 	atomic64_t mapped;
+	unsigned int pageshift;
 	u64 ua;			/* userspace address */
 	u64 entries;		/* number of entries in hpas[] */
 	u64 *hpas;		/* vmalloc'ed */

@@ -124,7 +125,7 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		struct mm_iommu_table_group_mem_t **pmem)
 {
 	struct mm_iommu_table_group_mem_t *mem;
-	long i, j, ret = 0, locked_entries = 0;
+	long i, j, ret = 0, locked_entries = 0, pageshift;
 	struct page *page = NULL;
 
 	mutex_lock(&mem_list_mutex);

@@ -166,6 +167,8 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		goto unlock_exit;
 	}
 
+	mem->pageshift = 30; /* start from 1G pages - the biggest we have */
+
 	for (i = 0; i < entries; ++i) {
 		if (1 != get_user_pages_fast(ua + (i << PAGE_SHIFT),
 					1/* pages */, 1/* iswrite */, &page)) {

@@ -199,6 +202,11 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 			}
 		}
 populate:
+		pageshift = PAGE_SHIFT;
+		if (PageCompound(page))
+			pageshift += compound_order(compound_head(page));
+		mem->pageshift = min_t(unsigned int, mem->pageshift, pageshift);
+
 		mem->hpas[i] = page_to_pfn(page) << PAGE_SHIFT;
 	}
 

@@ -349,7 +357,7 @@ struct mm_iommu_table_group_mem_t *mm_iommu_find(struct mm_struct *mm,
 EXPORT_SYMBOL_GPL(mm_iommu_find);
 
 long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
-		unsigned long ua, unsigned long *hpa)
+		unsigned long ua, unsigned int pageshift, unsigned long *hpa)
 {
 	const long entry = (ua - mem->ua) >> PAGE_SHIFT;
 	u64 *va = &mem->hpas[entry];

@@ -357,6 +365,9 @@ long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
 	if (entry >= mem->entries)
 		return -EFAULT;
 
+	if (pageshift > mem->pageshift)
+		return -EFAULT;
+
 	*hpa = *va | (ua & ~PAGE_MASK);
 
 	return 0;

@@ -364,7 +375,7 @@ long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
 EXPORT_SYMBOL_GPL(mm_iommu_ua_to_hpa);
 
 long mm_iommu_ua_to_hpa_rm(struct mm_iommu_table_group_mem_t *mem,
-		unsigned long ua, unsigned long *hpa)
+		unsigned long ua, unsigned int pageshift, unsigned long *hpa)
 {
 	const long entry = (ua - mem->ua) >> PAGE_SHIFT;
 	void *va = &mem->hpas[entry];

@@ -373,6 +384,9 @@ long mm_iommu_ua_to_hpa_rm(struct mm_iommu_table_group_mem_t *mem,
 	if (entry >= mem->entries)
 		return -EFAULT;
 
+	if (pageshift > mem->pageshift)
+		return -EFAULT;
+
 	pa = (void *) vmalloc_to_phys(va);
 	if (!pa)
 		return -EFAULT;

diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
index 2da5f05..7cd63b0 100644
--- a/drivers/vfio/vfio_iommu_spapr_tce.c
+++ b/drivers/vfio/vfio_iommu_spapr_tce.c

@@ -467,7 +467,7 @@ static int tce_iommu_prereg_ua_to_hpa(struct tce_container *container,
 	if (!mem)
 		return -EINVAL;
 
-	ret = mm_iommu_ua_to_hpa(mem, tce, phpa);
+	ret = mm_iommu_ua_to_hpa(mem, tce, shift, phpa);
 	if (ret)
 		return -EINVAL;
 

-- 
2.11.0

Alexey Kardashevskiy [off-list ref] writes:

This is to improve page boundaries checking and should probably
be cc:stable. I came accross this while debugging nvlink2 passthrough
but the lack of checking might be exploited by the existing userspace.

Do you really mean "exploited" ? As in there's a security issue?

Your change log for patch 2 sort of suggests that but then says that
without the fix you just hit an error in vfio code.

So I'm not clear on what the exposure is.

cheers

On Fri, 29 Jun 2018 11:55:40 +1000
Michael Ellerman [off-list ref] wrote:

Alexey Kardashevskiy [off-list ref] writes:

quoted

This is to improve page boundaries checking and should probably
be cc:stable. I came accross this while debugging nvlink2 passthrough
but the lack of checking might be exploited by the existing userspace.  

Do you really mean "exploited" ? As in there's a security issue?

Your change log for patch 2 sort of suggests that but then says that
without the fix you just hit an error in vfio code.

The bug is that I can easily make unmodified guest use 16MB IOMMU pages
while guest RAM is backed with system 64K pages so unless the guest RAM
is allocated contigously (which is unlikely), a 16MB TCE will provide
the hardware access to the host physical memory it is not supposed to
have access to, which is 16MB minus first 64K.

There is a fast path for H_PUT_TCE - via KVM - there is no contained
test.

There is a slow path for H_PUT_TCE - via VFIO ioctl() - there is a
contained test.

Because of a different feature of VFIO on sPAPR (it stores an array of
userspace addresses which we received from QEMU and translated to host
physical addresses and programmed those to the TCE table) we do not take
the fast path on the very first H_PUT_TCE (because I allocate the
array when the slow path is taken the very first time), fail there,
pass the failure to the guest the guest decides that is over.

But a modified guest could ignore that initial H_PUT_TCE failure and
simply repeat H_PUT_TCE again - this time it will take the fast path
and allow the bad mapping.

So I'm not clear on what the exposure is.

cheers

--
Alexey

On Tue, Jun 26, 2018 at 03:59:26PM +1000, Alexey Kardashevskiy wrote:

We already have a check in drivers/vfio/vfio_iommu_spapr_tce.c that
an IOMMU page is contained in the physical page so the PCI hardware won't
get access to unassigned host memory.

However we do not have this check in KVM fastpath (H_PUT_TCE accelerated
code) so the user space can pin memory backed with 64k pages and create
a hardware TCE table with a bigger page size. We were lucky so far and
did not hit this yet as the very first time the mapping happens
we do not have tbl::it_userspace allocated yet and fall back to
the userspace which in turn calls VFIO IOMMU driver and that fails
because of the check in vfio_iommu_spapr_tce.c which is really
sustainable solution.

This stores the smallest preregistered page size in the preregistered
region descriptor and changes the mm_iommu_xxx API to check this against
the IOMMU page size.

Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v2:
* explicitly check for compound pages before calling compound_order()

---
The bug is: run QEMU _without_ hugepages (no -mempath) and tell it to
advertise 16MB pages to the guest; a typical pseries guest will use 16MB
for IOMMU pages without checking the mmu pagesize and this will fail
at https://git.qemu.org/?p=qemu.git;a=blob;f=hw/vfio/common.c;h=fb396cf00ac40eb35967a04c9cc798ca896eed57;hb=refs/heads/master#l256

With the change, mapping will fail in KVM and the guest will print:

mlx5_core 0000:00:00.0: ibm,create-pe-dma-window(2027) 0 8000000 20000000 18 1f returned 0 (liobn = 0x80000001 starting addr = 8000000 0)
mlx5_core 0000:00:00.0: created tce table LIOBN 0x80000001 for /pci@800000020000000/ethernet@0
mlx5_core 0000:00:00.0: failed to map direct window for
/pci@800000020000000/ethernet@0: -1

[snip]

What about 16G pages on an HPT system?

Why not make mem->pageshift and pageshift local the same type to avoid
the min_t() ?

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

On Fri, Jun 29, 2018 at 01:00:07PM +1000, Alexey Kardashevskiy wrote:

On Fri, 29 Jun 2018 11:55:40 +1000
Michael Ellerman [off-list ref] wrote:

quoted

Alexey Kardashevskiy [off-list ref] writes:

quoted

This is to improve page boundaries checking and should probably
be cc:stable. I came accross this while debugging nvlink2 passthrough
but the lack of checking might be exploited by the existing userspace.  

Do you really mean "exploited" ? As in there's a security issue?

Your change log for patch 2 sort of suggests that but then says that
without the fix you just hit an error in vfio code.

The bug is that I can easily make unmodified guest use 16MB IOMMU pages
while guest RAM is backed with system 64K pages so unless the guest RAM
is allocated contigously (which is unlikely), a 16MB TCE will provide
the hardware access to the host physical memory it is not supposed to
have access to, which is 16MB minus first 64K.

There is a fast path for H_PUT_TCE - via KVM - there is no contained
test.

There is a slow path for H_PUT_TCE - via VFIO ioctl() - there is a
contained test.

Because of a different feature of VFIO on sPAPR (it stores an array of
userspace addresses which we received from QEMU and translated to host
physical addresses and programmed those to the TCE table) we do not take
the fast path on the very first H_PUT_TCE (because I allocate the
array when the slow path is taken the very first time), fail there,
pass the failure to the guest the guest decides that is over.

But a modified guest could ignore that initial H_PUT_TCE failure and
simply repeat H_PUT_TCE again - this time it will take the fast path
and allow the bad mapping.

In short, yes, it's an exploitable security hole in the host.  An
unmodified Linux guest kernel just doesn't happen to exploit it, even
if the guest userspace tries to get it to.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

On Fri, 29 Jun 2018 14:12:41 +1000
David Gibson [off-list ref] wrote:

On Tue, Jun 26, 2018 at 03:59:26PM +1000, Alexey Kardashevskiy wrote:

quoted

We already have a check in drivers/vfio/vfio_iommu_spapr_tce.c that
an IOMMU page is contained in the physical page so the PCI hardware won't
get access to unassigned host memory.

However we do not have this check in KVM fastpath (H_PUT_TCE accelerated
code) so the user space can pin memory backed with 64k pages and create
a hardware TCE table with a bigger page size. We were lucky so far and
did not hit this yet as the very first time the mapping happens
we do not have tbl::it_userspace allocated yet and fall back to
the userspace which in turn calls VFIO IOMMU driver and that fails
because of the check in vfio_iommu_spapr_tce.c which is really
sustainable solution.

This stores the smallest preregistered page size in the preregistered
region descriptor and changes the mm_iommu_xxx API to check this against
the IOMMU page size.

Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v2:
* explicitly check for compound pages before calling compound_order()

---
The bug is: run QEMU _without_ hugepages (no -mempath) and tell it to
advertise 16MB pages to the guest; a typical pseries guest will use 16MB
for IOMMU pages without checking the mmu pagesize and this will fail
at https://git.qemu.org/?p=qemu.git;a=blob;f=hw/vfio/common.c;h=fb396cf00ac40eb35967a04c9cc798ca896eed57;hb=refs/heads/master#l256

With the change, mapping will fail in KVM and the guest will print:

mlx5_core 0000:00:00.0: ibm,create-pe-dma-window(2027) 0 8000000 20000000 18 1f returned 0 (liobn = 0x80000001 starting addr = 8000000 0)
mlx5_core 0000:00:00.0: created tce table LIOBN 0x80000001 for /pci@800000020000000/ethernet@0
mlx5_core 0000:00:00.0: failed to map direct window for
/pci@800000020000000/ethernet@0: -1  

[snip]

quoted

@@ -124,7 +125,7 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		struct mm_iommu_table_group_mem_t **pmem)
 {
 	struct mm_iommu_table_group_mem_t *mem;
-	long i, j, ret = 0, locked_entries = 0;
+	long i, j, ret = 0, locked_entries = 0, pageshift;
 	struct page *page = NULL;
 
 	mutex_lock(&mem_list_mutex);

@@ -166,6 +167,8 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		goto unlock_exit;
 	}
 

 > > +	mem->pageshift = 30; /* start from 1G pages - the biggest we have */  

What about 16G pages on an HPT system?

Below in the loop mem->pageshift will reduce to the biggest actual size
which will be 16mb/64k/4k. Or remain 1GB if no memory is actually
pinned, no loss there.

quoted

 	for (i = 0; i < entries; ++i) {
 		if (1 != get_user_pages_fast(ua + (i << PAGE_SHIFT),
 					1/* pages */, 1/* iswrite */, &page)) {

@@ -199,6 +202,11 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 			}
 		}
 populate:
+		pageshift = PAGE_SHIFT;
+		if (PageCompound(page))
+			pageshift += compound_order(compound_head(page));
+		mem->pageshift = min_t(unsigned int, mem->pageshift, pageshift);  

Why not make mem->pageshift and pageshift local the same type to avoid
the min_t() ?

I was under impression min() is deprecated (misinterpret checkpatch.pl
may be) and therefore did not pay attention to it. I can fix this and
repost if there is no other question.

quoted

+
 		mem->hpas[i] = page_to_pfn(page) << PAGE_SHIFT;
 	}
 

@@ -349,7 +357,7 @@ struct mm_iommu_table_group_mem_t *mm_iommu_find(struct mm_struct *mm,
 EXPORT_SYMBOL_GPL(mm_iommu_find);
 
 long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
-		unsigned long ua, unsigned long *hpa)
+		unsigned long ua, unsigned int pageshift, unsigned long *hpa)
 {
 	const long entry = (ua - mem->ua) >> PAGE_SHIFT;
 	u64 *va = &mem->hpas[entry];

@@ -357,6 +365,9 @@ long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
 	if (entry >= mem->entries)
 		return -EFAULT;
 
+	if (pageshift > mem->pageshift)
+		return -EFAULT;
+
 	*hpa = *va | (ua & ~PAGE_MASK);
 
 	return 0;

@@ -364,7 +375,7 @@ long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
 EXPORT_SYMBOL_GPL(mm_iommu_ua_to_hpa);
 
 long mm_iommu_ua_to_hpa_rm(struct mm_iommu_table_group_mem_t *mem,
-		unsigned long ua, unsigned long *hpa)
+		unsigned long ua, unsigned int pageshift, unsigned long *hpa)
 {
 	const long entry = (ua - mem->ua) >> PAGE_SHIFT;
 	void *va = &mem->hpas[entry];

@@ -373,6 +384,9 @@ long mm_iommu_ua_to_hpa_rm(struct mm_iommu_table_group_mem_t *mem,
 	if (entry >= mem->entries)
 		return -EFAULT;
 
+	if (pageshift > mem->pageshift)
+		return -EFAULT;
+
 	pa = (void *) vmalloc_to_phys(va);
 	if (!pa)
 		return -EFAULT;

diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
index 2da5f05..7cd63b0 100644
--- a/drivers/vfio/vfio_iommu_spapr_tce.c
+++ b/drivers/vfio/vfio_iommu_spapr_tce.c

@@ -467,7 +467,7 @@ static int tce_iommu_prereg_ua_to_hpa(struct tce_container *container,
 	if (!mem)
 		return -EINVAL;
 
-	ret = mm_iommu_ua_to_hpa(mem, tce, phpa);
+	ret = mm_iommu_ua_to_hpa(mem, tce, shift, phpa);
 	if (ret)
 		return -EINVAL;
   

--
Alexey

On Fri, Jun 29, 2018 at 02:51:21PM +1000, Alexey Kardashevskiy wrote:

On Fri, 29 Jun 2018 14:12:41 +1000
David Gibson [off-list ref] wrote:

quoted

On Tue, Jun 26, 2018 at 03:59:26PM +1000, Alexey Kardashevskiy wrote:

quoted

We already have a check in drivers/vfio/vfio_iommu_spapr_tce.c that
an IOMMU page is contained in the physical page so the PCI hardware won't
get access to unassigned host memory.

However we do not have this check in KVM fastpath (H_PUT_TCE accelerated
code) so the user space can pin memory backed with 64k pages and create
a hardware TCE table with a bigger page size. We were lucky so far and
did not hit this yet as the very first time the mapping happens
we do not have tbl::it_userspace allocated yet and fall back to
the userspace which in turn calls VFIO IOMMU driver and that fails
because of the check in vfio_iommu_spapr_tce.c which is really
sustainable solution.

This stores the smallest preregistered page size in the preregistered
region descriptor and changes the mm_iommu_xxx API to check this against
the IOMMU page size.

Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v2:
* explicitly check for compound pages before calling compound_order()

---
The bug is: run QEMU _without_ hugepages (no -mempath) and tell it to
advertise 16MB pages to the guest; a typical pseries guest will use 16MB
for IOMMU pages without checking the mmu pagesize and this will fail
at https://git.qemu.org/?p=qemu.git;a=blob;f=hw/vfio/common.c;h=fb396cf00ac40eb35967a04c9cc798ca896eed57;hb=refs/heads/master#l256

With the change, mapping will fail in KVM and the guest will print:

mlx5_core 0000:00:00.0: ibm,create-pe-dma-window(2027) 0 8000000 20000000 18 1f returned 0 (liobn = 0x80000001 starting addr = 8000000 0)
mlx5_core 0000:00:00.0: created tce table LIOBN 0x80000001 for /pci@800000020000000/ethernet@0
mlx5_core 0000:00:00.0: failed to map direct window for
/pci@800000020000000/ethernet@0: -1  

[snip]

quoted

@@ -124,7 +125,7 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		struct mm_iommu_table_group_mem_t **pmem)
 {
 	struct mm_iommu_table_group_mem_t *mem;
-	long i, j, ret = 0, locked_entries = 0;
+	long i, j, ret = 0, locked_entries = 0, pageshift;
 	struct page *page = NULL;
 
 	mutex_lock(&mem_list_mutex);

@@ -166,6 +167,8 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		goto unlock_exit;
 	}
 

 > > +	mem->pageshift = 30; /* start from 1G pages - the biggest we have */  

quoted

What about 16G pages on an HPT system?

Below in the loop mem->pageshift will reduce to the biggest actual size
which will be 16mb/64k/4k. Or remain 1GB if no memory is actually
pinned, no loss there.

Are you saying that 16G IOMMU pages aren't supported?  Or that there's
some reason a guest can never use them?

quoted

quoted

 	for (i = 0; i < entries; ++i) {
 		if (1 != get_user_pages_fast(ua + (i << PAGE_SHIFT),
 					1/* pages */, 1/* iswrite */, &page)) {

@@ -199,6 +202,11 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 			}
 		}
 populate:
+		pageshift = PAGE_SHIFT;
+		if (PageCompound(page))
+			pageshift += compound_order(compound_head(page));
+		mem->pageshift = min_t(unsigned int, mem->pageshift, pageshift);  

Why not make mem->pageshift and pageshift local the same type to avoid
the min_t() ?

I was under impression min() is deprecated (misinterpret checkpatch.pl
may be) and therefore did not pay attention to it. I can fix this and
repost if there is no other question.

Hm, it's possible.


-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

On Fri, 29 Jun 2018 14:57:02 +1000
David Gibson [off-list ref] wrote:

On Fri, Jun 29, 2018 at 02:51:21PM +1000, Alexey Kardashevskiy wrote:

quoted

On Fri, 29 Jun 2018 14:12:41 +1000
David Gibson [off-list ref] wrote:
  

quoted

On Tue, Jun 26, 2018 at 03:59:26PM +1000, Alexey Kardashevskiy wrote:  

quoted

We already have a check in drivers/vfio/vfio_iommu_spapr_tce.c that
an IOMMU page is contained in the physical page so the PCI hardware won't
get access to unassigned host memory.

However we do not have this check in KVM fastpath (H_PUT_TCE accelerated
code) so the user space can pin memory backed with 64k pages and create
a hardware TCE table with a bigger page size. We were lucky so far and
did not hit this yet as the very first time the mapping happens
we do not have tbl::it_userspace allocated yet and fall back to
the userspace which in turn calls VFIO IOMMU driver and that fails
because of the check in vfio_iommu_spapr_tce.c which is really
sustainable solution.

This stores the smallest preregistered page size in the preregistered
region descriptor and changes the mm_iommu_xxx API to check this against
the IOMMU page size.

Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v2:
* explicitly check for compound pages before calling compound_order()

---
The bug is: run QEMU _without_ hugepages (no -mempath) and tell it to
advertise 16MB pages to the guest; a typical pseries guest will use 16MB
for IOMMU pages without checking the mmu pagesize and this will fail
at https://git.qemu.org/?p=qemu.git;a=blob;f=hw/vfio/common.c;h=fb396cf00ac40eb35967a04c9cc798ca896eed57;hb=refs/heads/master#l256

With the change, mapping will fail in KVM and the guest will print:

mlx5_core 0000:00:00.0: ibm,create-pe-dma-window(2027) 0 8000000 20000000 18 1f returned 0 (liobn = 0x80000001 starting addr = 8000000 0)
mlx5_core 0000:00:00.0: created tce table LIOBN 0x80000001 for /pci@800000020000000/ethernet@0
mlx5_core 0000:00:00.0: failed to map direct window for
/pci@800000020000000/ethernet@0: -1    

[snip]  

quoted

@@ -124,7 +125,7 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		struct mm_iommu_table_group_mem_t **pmem)
 {
 	struct mm_iommu_table_group_mem_t *mem;
-	long i, j, ret = 0, locked_entries = 0;
+	long i, j, ret = 0, locked_entries = 0, pageshift;
 	struct page *page = NULL;
 
 	mutex_lock(&mem_list_mutex);

@@ -166,6 +167,8 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		goto unlock_exit;
 	}
 

 > > +	mem->pageshift = 30; /* start from 1G pages - the biggest we have */    

quoted

What about 16G pages on an HPT system?  

Below in the loop mem->pageshift will reduce to the biggest actual size
which will be 16mb/64k/4k. Or remain 1GB if no memory is actually
pinned, no loss there.  

Are you saying that 16G IOMMU pages aren't supported?  Or that there's
some reason a guest can never use them?

ah, 16_G_, not _M_. My bad. I just never tried such huge pages, I will
lift the limit up to 64 then, easier this way.

quoted

quoted

quoted

 	for (i = 0; i < entries; ++i) {
 		if (1 != get_user_pages_fast(ua + (i << PAGE_SHIFT),
 					1/* pages */, 1/* iswrite */, &page)) {

@@ -199,6 +202,11 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 			}
 		}
 populate:
+		pageshift = PAGE_SHIFT;
+		if (PageCompound(page))
+			pageshift += compound_order(compound_head(page));
+		mem->pageshift = min_t(unsigned int, mem->pageshift, pageshift);    

Why not make mem->pageshift and pageshift local the same type to avoid
the min_t() ?  

I was under impression min() is deprecated (misinterpret checkpatch.pl
may be) and therefore did not pay attention to it. I can fix this and
repost if there is no other question.  

Hm, it's possible.

Nah, tried min(), compiles fine.



--
Alexey

On Fri, 29 Jun 2018 15:18:20 +1000
Alexey Kardashevskiy [off-list ref] wrote:

On Fri, 29 Jun 2018 14:57:02 +1000
David Gibson [off-list ref] wrote:

quoted

On Fri, Jun 29, 2018 at 02:51:21PM +1000, Alexey Kardashevskiy wrote:  

quoted

On Fri, 29 Jun 2018 14:12:41 +1000
David Gibson [off-list ref] wrote:
    

quoted

On Tue, Jun 26, 2018 at 03:59:26PM +1000, Alexey Kardashevskiy wrote:    

quoted

We already have a check in drivers/vfio/vfio_iommu_spapr_tce.c that
an IOMMU page is contained in the physical page so the PCI hardware won't
get access to unassigned host memory.

However we do not have this check in KVM fastpath (H_PUT_TCE accelerated
code) so the user space can pin memory backed with 64k pages and create
a hardware TCE table with a bigger page size. We were lucky so far and
did not hit this yet as the very first time the mapping happens
we do not have tbl::it_userspace allocated yet and fall back to
the userspace which in turn calls VFIO IOMMU driver and that fails
because of the check in vfio_iommu_spapr_tce.c which is really
sustainable solution.

This stores the smallest preregistered page size in the preregistered
region descriptor and changes the mm_iommu_xxx API to check this against
the IOMMU page size.

Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v2:
* explicitly check for compound pages before calling compound_order()

---
The bug is: run QEMU _without_ hugepages (no -mempath) and tell it to
advertise 16MB pages to the guest; a typical pseries guest will use 16MB
for IOMMU pages without checking the mmu pagesize and this will fail
at https://git.qemu.org/?p=qemu.git;a=blob;f=hw/vfio/common.c;h=fb396cf00ac40eb35967a04c9cc798ca896eed57;hb=refs/heads/master#l256

With the change, mapping will fail in KVM and the guest will print:

mlx5_core 0000:00:00.0: ibm,create-pe-dma-window(2027) 0 8000000 20000000 18 1f returned 0 (liobn = 0x80000001 starting addr = 8000000 0)
mlx5_core 0000:00:00.0: created tce table LIOBN 0x80000001 for /pci@800000020000000/ethernet@0
mlx5_core 0000:00:00.0: failed to map direct window for
/pci@800000020000000/ethernet@0: -1      

[snip]    

quoted

@@ -124,7 +125,7 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		struct mm_iommu_table_group_mem_t **pmem)
 {
 	struct mm_iommu_table_group_mem_t *mem;
-	long i, j, ret = 0, locked_entries = 0;
+	long i, j, ret = 0, locked_entries = 0, pageshift;
 	struct page *page = NULL;
 
 	mutex_lock(&mem_list_mutex);

@@ -166,6 +167,8 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		goto unlock_exit;
 	}
 

 > > +	mem->pageshift = 30; /* start from 1G pages - the biggest we have */      

quoted

What about 16G pages on an HPT system?    

Below in the loop mem->pageshift will reduce to the biggest actual size
which will be 16mb/64k/4k. Or remain 1GB if no memory is actually
pinned, no loss there.    

Are you saying that 16G IOMMU pages aren't supported?  Or that there's
some reason a guest can never use them?  

ah, 16_G_, not _M_. My bad. I just never tried such huge pages, I will
lift the limit up to 64 then, easier this way.

Ah, no, rather this as the upper limit:

mem->pageshift = ilog2(entries) + PAGE_SHIFT;


@entries here is a number of system pages being pinned in that
function.

quoted

quoted

quoted

quoted

 	for (i = 0; i < entries; ++i) {
 		if (1 != get_user_pages_fast(ua + (i << PAGE_SHIFT),
 					1/* pages */, 1/* iswrite */, &page)) {

@@ -199,6 +202,11 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 			}
 		}
 populate:
+		pageshift = PAGE_SHIFT;
+		if (PageCompound(page))
+			pageshift += compound_order(compound_head(page));
+		mem->pageshift = min_t(unsigned int, mem->pageshift, pageshift);      

Why not make mem->pageshift and pageshift local the same type to avoid
the min_t() ?    

I was under impression min() is deprecated (misinterpret checkpatch.pl
may be) and therefore did not pay attention to it. I can fix this and
repost if there is no other question.    

Hm, it's possible.  

Nah, tried min(), compiles fine.

--
Alexey

On Tue, 26 Jun 2018 15:59:25 +1000
Alexey Kardashevskiy [off-list ref] wrote:

The size is always equal to 1 page so let's use this. Later on this will
be used for other checks which use page shifts to check the granularity
of access.

This should cause no behavioral change.

Reviewed-by: David Gibson <redacted>
Signed-off-by: Alexey Kardashevskiy <redacted>
---
 drivers/vfio/vfio_iommu_spapr_tce.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

I assume a v3+ will go in through the ppc tree since the bulk of the
series is there.  For this,

Acked-by: Alex Williamson <redacted>

On Fri, Jun 29, 2018 at 05:07:47PM +1000, Alexey Kardashevskiy wrote:

On Fri, 29 Jun 2018 15:18:20 +1000
Alexey Kardashevskiy [off-list ref] wrote:

quoted

On Fri, 29 Jun 2018 14:57:02 +1000
David Gibson [off-list ref] wrote:

quoted

On Fri, Jun 29, 2018 at 02:51:21PM +1000, Alexey Kardashevskiy wrote:  

quoted

On Fri, 29 Jun 2018 14:12:41 +1000
David Gibson [off-list ref] wrote:
    

quoted

On Tue, Jun 26, 2018 at 03:59:26PM +1000, Alexey Kardashevskiy wrote:    

quoted

We already have a check in drivers/vfio/vfio_iommu_spapr_tce.c that
an IOMMU page is contained in the physical page so the PCI hardware won't
get access to unassigned host memory.

However we do not have this check in KVM fastpath (H_PUT_TCE accelerated
code) so the user space can pin memory backed with 64k pages and create
a hardware TCE table with a bigger page size. We were lucky so far and
did not hit this yet as the very first time the mapping happens
we do not have tbl::it_userspace allocated yet and fall back to
the userspace which in turn calls VFIO IOMMU driver and that fails
because of the check in vfio_iommu_spapr_tce.c which is really
sustainable solution.

This stores the smallest preregistered page size in the preregistered
region descriptor and changes the mm_iommu_xxx API to check this against
the IOMMU page size.

Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v2:
* explicitly check for compound pages before calling compound_order()

---
The bug is: run QEMU _without_ hugepages (no -mempath) and tell it to
advertise 16MB pages to the guest; a typical pseries guest will use 16MB
for IOMMU pages without checking the mmu pagesize and this will fail
at https://git.qemu.org/?p=qemu.git;a=blob;f=hw/vfio/common.c;h=fb396cf00ac40eb35967a04c9cc798ca896eed57;hb=refs/heads/master#l256

With the change, mapping will fail in KVM and the guest will print:

mlx5_core 0000:00:00.0: ibm,create-pe-dma-window(2027) 0 8000000 20000000 18 1f returned 0 (liobn = 0x80000001 starting addr = 8000000 0)
mlx5_core 0000:00:00.0: created tce table LIOBN 0x80000001 for /pci@800000020000000/ethernet@0
mlx5_core 0000:00:00.0: failed to map direct window for
/pci@800000020000000/ethernet@0: -1      

[snip]    

quoted

@@ -124,7 +125,7 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		struct mm_iommu_table_group_mem_t **pmem)
 {
 	struct mm_iommu_table_group_mem_t *mem;
-	long i, j, ret = 0, locked_entries = 0;
+	long i, j, ret = 0, locked_entries = 0, pageshift;
 	struct page *page = NULL;
 
 	mutex_lock(&mem_list_mutex);

@@ -166,6 +167,8 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		goto unlock_exit;
 	}
 

 > > +	mem->pageshift = 30; /* start from 1G pages - the biggest we have */      

quoted

What about 16G pages on an HPT system?    

Below in the loop mem->pageshift will reduce to the biggest actual size
which will be 16mb/64k/4k. Or remain 1GB if no memory is actually
pinned, no loss there.    

Are you saying that 16G IOMMU pages aren't supported?  Or that there's
some reason a guest can never use them?  

ah, 16_G_, not _M_. My bad. I just never tried such huge pages, I will
lift the limit up to 64 then, easier this way.

Ah, no, rather this as the upper limit:

mem->pageshift = ilog2(entries) + PAGE_SHIFT;

I can't make sense of this comment in context.  I see how you're
computing the minimum page size in the reserved region.

My question is about what the "maximum minimum" is - the starting
value from which you calculate.  Currently it's 1G, but I can't
immediately see a reason that 16G is impossible here.

@entries here is a number of system pages being pinned in that
function.

quoted

quoted

quoted

quoted

quoted

 	for (i = 0; i < entries; ++i) {
 		if (1 != get_user_pages_fast(ua + (i << PAGE_SHIFT),
 					1/* pages */, 1/* iswrite */, &page)) {

@@ -199,6 +202,11 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 			}
 		}
 populate:
+		pageshift = PAGE_SHIFT;
+		if (PageCompound(page))
+			pageshift += compound_order(compound_head(page));
+		mem->pageshift = min_t(unsigned int, mem->pageshift, pageshift);      

Why not make mem->pageshift and pageshift local the same type to avoid
the min_t() ?    

I was under impression min() is deprecated (misinterpret checkpatch.pl
may be) and therefore did not pay attention to it. I can fix this and
repost if there is no other question.    

Hm, it's possible.  

Nah, tried min(), compiles fine.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

On Mon, 2 Jul 2018 14:08:52 +1000
David Gibson [off-list ref] wrote:

On Fri, Jun 29, 2018 at 05:07:47PM +1000, Alexey Kardashevskiy wrote:

quoted

On Fri, 29 Jun 2018 15:18:20 +1000
Alexey Kardashevskiy [off-list ref] wrote:
  

quoted

On Fri, 29 Jun 2018 14:57:02 +1000
David Gibson [off-list ref] wrote:
  

quoted

On Fri, Jun 29, 2018 at 02:51:21PM +1000, Alexey Kardashevskiy wrote:    

quoted

On Fri, 29 Jun 2018 14:12:41 +1000
David Gibson [off-list ref] wrote:
      

quoted

On Tue, Jun 26, 2018 at 03:59:26PM +1000, Alexey Kardashevskiy wrote:      

quoted

We already have a check in drivers/vfio/vfio_iommu_spapr_tce.c that
an IOMMU page is contained in the physical page so the PCI hardware won't
get access to unassigned host memory.

However we do not have this check in KVM fastpath (H_PUT_TCE accelerated
code) so the user space can pin memory backed with 64k pages and create
a hardware TCE table with a bigger page size. We were lucky so far and
did not hit this yet as the very first time the mapping happens
we do not have tbl::it_userspace allocated yet and fall back to
the userspace which in turn calls VFIO IOMMU driver and that fails
because of the check in vfio_iommu_spapr_tce.c which is really
sustainable solution.

This stores the smallest preregistered page size in the preregistered
region descriptor and changes the mm_iommu_xxx API to check this against
the IOMMU page size.

Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v2:
* explicitly check for compound pages before calling compound_order()

---
The bug is: run QEMU _without_ hugepages (no -mempath) and tell it to
advertise 16MB pages to the guest; a typical pseries guest will use 16MB
for IOMMU pages without checking the mmu pagesize and this will fail
at https://git.qemu.org/?p=qemu.git;a=blob;f=hw/vfio/common.c;h=fb396cf00ac40eb35967a04c9cc798ca896eed57;hb=refs/heads/master#l256

With the change, mapping will fail in KVM and the guest will print:

mlx5_core 0000:00:00.0: ibm,create-pe-dma-window(2027) 0 8000000 20000000 18 1f returned 0 (liobn = 0x80000001 starting addr = 8000000 0)
mlx5_core 0000:00:00.0: created tce table LIOBN 0x80000001 for /pci@800000020000000/ethernet@0
mlx5_core 0000:00:00.0: failed to map direct window for
/pci@800000020000000/ethernet@0: -1        

[snip]      

quoted

@@ -124,7 +125,7 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		struct mm_iommu_table_group_mem_t **pmem)
 {
 	struct mm_iommu_table_group_mem_t *mem;
-	long i, j, ret = 0, locked_entries = 0;
+	long i, j, ret = 0, locked_entries = 0, pageshift;
 	struct page *page = NULL;
 
 	mutex_lock(&mem_list_mutex);

@@ -166,6 +167,8 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		goto unlock_exit;
 	}
 

 > > +	mem->pageshift = 30; /* start from 1G pages - the biggest we have */        

quoted

What about 16G pages on an HPT system?      

Below in the loop mem->pageshift will reduce to the biggest actual size
which will be 16mb/64k/4k. Or remain 1GB if no memory is actually
pinned, no loss there.      

Are you saying that 16G IOMMU pages aren't supported?  Or that there's
some reason a guest can never use them?    

ah, 16_G_, not _M_. My bad. I just never tried such huge pages, I will
lift the limit up to 64 then, easier this way.  

Ah, no, rather this as the upper limit:

mem->pageshift = ilog2(entries) + PAGE_SHIFT;  

I can't make sense of this comment in context.  I see how you're
computing the minimum page size in the reserved region.

My question is about what the "maximum minimum" is - the starting
value from which you calculate.  Currently it's 1G, but I can't
immediately see a reason that 16G is impossible here.

16GB is impossible if the chunk we are preregistering here is smaller
than that, for example, the entire guest ram is 4GB. If that is the
case and we try mapping a 16GB IOMMU page, this should fail as I do not
really know what happens to the memory between 4GB..16GB.

imho if not that, than 1<<64 would make a good upper limit.

quoted

@entries here is a number of system pages being pinned in that
function.


  

quoted

quoted

quoted

quoted

quoted

 	for (i = 0; i < entries; ++i) {
 		if (1 != get_user_pages_fast(ua + (i << PAGE_SHIFT),
 					1/* pages */, 1/* iswrite */, &page)) {

@@ -199,6 +202,11 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 			}
 		}
 populate:
+		pageshift = PAGE_SHIFT;
+		if (PageCompound(page))
+			pageshift += compound_order(compound_head(page));
+		mem->pageshift = min_t(unsigned int, mem->pageshift, pageshift);        

Why not make mem->pageshift and pageshift local the same type to avoid
the min_t() ?      

I was under impression min() is deprecated (misinterpret checkpatch.pl
may be) and therefore did not pay attention to it. I can fix this and
repost if there is no other question.      

Hm, it's possible.    

Nah, tried min(), compiles fine.  

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

--
Alexey

On Mon, Jul 02, 2018 at 02:33:30PM +1000, Alexey Kardashevskiy wrote:

On Mon, 2 Jul 2018 14:08:52 +1000
David Gibson [off-list ref] wrote:

quoted

On Fri, Jun 29, 2018 at 05:07:47PM +1000, Alexey Kardashevskiy wrote:

quoted

On Fri, 29 Jun 2018 15:18:20 +1000
Alexey Kardashevskiy [off-list ref] wrote:
  

quoted

On Fri, 29 Jun 2018 14:57:02 +1000
David Gibson [off-list ref] wrote:
  

quoted

On Fri, Jun 29, 2018 at 02:51:21PM +1000, Alexey Kardashevskiy wrote:    

quoted

On Fri, 29 Jun 2018 14:12:41 +1000
David Gibson [off-list ref] wrote:
      

quoted

On Tue, Jun 26, 2018 at 03:59:26PM +1000, Alexey Kardashevskiy wrote:      

quoted

We already have a check in drivers/vfio/vfio_iommu_spapr_tce.c that
an IOMMU page is contained in the physical page so the PCI hardware won't
get access to unassigned host memory.

However we do not have this check in KVM fastpath (H_PUT_TCE accelerated
code) so the user space can pin memory backed with 64k pages and create
a hardware TCE table with a bigger page size. We were lucky so far and
did not hit this yet as the very first time the mapping happens
we do not have tbl::it_userspace allocated yet and fall back to
the userspace which in turn calls VFIO IOMMU driver and that fails
because of the check in vfio_iommu_spapr_tce.c which is really
sustainable solution.

This stores the smallest preregistered page size in the preregistered
region descriptor and changes the mm_iommu_xxx API to check this against
the IOMMU page size.

Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v2:
* explicitly check for compound pages before calling compound_order()

---
The bug is: run QEMU _without_ hugepages (no -mempath) and tell it to
advertise 16MB pages to the guest; a typical pseries guest will use 16MB
for IOMMU pages without checking the mmu pagesize and this will fail
at https://git.qemu.org/?p=qemu.git;a=blob;f=hw/vfio/common.c;h=fb396cf00ac40eb35967a04c9cc798ca896eed57;hb=refs/heads/master#l256

With the change, mapping will fail in KVM and the guest will print:

mlx5_core 0000:00:00.0: ibm,create-pe-dma-window(2027) 0 8000000 20000000 18 1f returned 0 (liobn = 0x80000001 starting addr = 8000000 0)
mlx5_core 0000:00:00.0: created tce table LIOBN 0x80000001 for /pci@800000020000000/ethernet@0
mlx5_core 0000:00:00.0: failed to map direct window for
/pci@800000020000000/ethernet@0: -1        

[snip]      

quoted

@@ -124,7 +125,7 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		struct mm_iommu_table_group_mem_t **pmem)
 {
 	struct mm_iommu_table_group_mem_t *mem;
-	long i, j, ret = 0, locked_entries = 0;
+	long i, j, ret = 0, locked_entries = 0, pageshift;
 	struct page *page = NULL;
 
 	mutex_lock(&mem_list_mutex);

@@ -166,6 +167,8 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		goto unlock_exit;
 	}
 

 > > +	mem->pageshift = 30; /* start from 1G pages - the biggest we have */        

quoted

What about 16G pages on an HPT system?      

Below in the loop mem->pageshift will reduce to the biggest actual size
which will be 16mb/64k/4k. Or remain 1GB if no memory is actually
pinned, no loss there.      

Are you saying that 16G IOMMU pages aren't supported?  Or that there's
some reason a guest can never use them?    

ah, 16_G_, not _M_. My bad. I just never tried such huge pages, I will
lift the limit up to 64 then, easier this way.  

Ah, no, rather this as the upper limit:

mem->pageshift = ilog2(entries) + PAGE_SHIFT;  

I can't make sense of this comment in context.  I see how you're
computing the minimum page size in the reserved region.

My question is about what the "maximum minimum" is - the starting
value from which you calculate.  Currently it's 1G, but I can't
immediately see a reason that 16G is impossible here.

16GB is impossible if the chunk we are preregistering here is smaller
than that, for example, the entire guest ram is 4GB.

Of course.  Just like it was for 1GiB if you had a 512MiB guest, for
example.  I'm talking about a case where you have a guest that's

=16GiB and you *have* allocated 16GiB hugepages to back it.

If that is the
case and we try mapping a 16GB IOMMU page, this should fail as I do not
really know what happens to the memory between 4GB..16GB.

imho if not that, than 1<<64 would make a good upper limit.

quoted

quoted

@entries here is a number of system pages being pinned in that
function.


  

quoted

quoted

quoted

quoted

quoted

 	for (i = 0; i < entries; ++i) {
 		if (1 != get_user_pages_fast(ua + (i << PAGE_SHIFT),
 					1/* pages */, 1/* iswrite */, &page)) {

@@ -199,6 +202,11 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 			}
 		}
 populate:
+		pageshift = PAGE_SHIFT;
+		if (PageCompound(page))
+			pageshift += compound_order(compound_head(page));
+		mem->pageshift = min_t(unsigned int, mem->pageshift, pageshift);        

Why not make mem->pageshift and pageshift local the same type to avoid
the min_t() ?      

I was under impression min() is deprecated (misinterpret checkpatch.pl
may be) and therefore did not pay attention to it. I can fix this and
repost if there is no other question.      

Hm, it's possible.    

Nah, tried min(), compiles fine.  

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

On Mon, 2 Jul 2018 14:52:43 +1000
David Gibson [off-list ref] wrote:

On Mon, Jul 02, 2018 at 02:33:30PM +1000, Alexey Kardashevskiy wrote:

quoted

On Mon, 2 Jul 2018 14:08:52 +1000
David Gibson [off-list ref] wrote:
  

quoted

On Fri, Jun 29, 2018 at 05:07:47PM +1000, Alexey Kardashevskiy wrote:  

quoted

On Fri, 29 Jun 2018 15:18:20 +1000
Alexey Kardashevskiy [off-list ref] wrote:
    

quoted

On Fri, 29 Jun 2018 14:57:02 +1000
David Gibson [off-list ref] wrote:
    

quoted

On Fri, Jun 29, 2018 at 02:51:21PM +1000, Alexey Kardashevskiy wrote:      

quoted

On Fri, 29 Jun 2018 14:12:41 +1000
David Gibson [off-list ref] wrote:
        

quoted

On Tue, Jun 26, 2018 at 03:59:26PM +1000, Alexey Kardashevskiy wrote:        

quoted

We already have a check in drivers/vfio/vfio_iommu_spapr_tce.c that
an IOMMU page is contained in the physical page so the PCI hardware won't
get access to unassigned host memory.

However we do not have this check in KVM fastpath (H_PUT_TCE accelerated
code) so the user space can pin memory backed with 64k pages and create
a hardware TCE table with a bigger page size. We were lucky so far and
did not hit this yet as the very first time the mapping happens
we do not have tbl::it_userspace allocated yet and fall back to
the userspace which in turn calls VFIO IOMMU driver and that fails
because of the check in vfio_iommu_spapr_tce.c which is really
sustainable solution.

This stores the smallest preregistered page size in the preregistered
region descriptor and changes the mm_iommu_xxx API to check this against
the IOMMU page size.

Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v2:
* explicitly check for compound pages before calling compound_order()

---
The bug is: run QEMU _without_ hugepages (no -mempath) and tell it to
advertise 16MB pages to the guest; a typical pseries guest will use 16MB
for IOMMU pages without checking the mmu pagesize and this will fail
at https://git.qemu.org/?p=qemu.git;a=blob;f=hw/vfio/common.c;h=fb396cf00ac40eb35967a04c9cc798ca896eed57;hb=refs/heads/master#l256

With the change, mapping will fail in KVM and the guest will print:

mlx5_core 0000:00:00.0: ibm,create-pe-dma-window(2027) 0 8000000 20000000 18 1f returned 0 (liobn = 0x80000001 starting addr = 8000000 0)
mlx5_core 0000:00:00.0: created tce table LIOBN 0x80000001 for /pci@800000020000000/ethernet@0
mlx5_core 0000:00:00.0: failed to map direct window for
/pci@800000020000000/ethernet@0: -1          

[snip]        

quoted

@@ -124,7 +125,7 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		struct mm_iommu_table_group_mem_t **pmem)
 {
 	struct mm_iommu_table_group_mem_t *mem;
-	long i, j, ret = 0, locked_entries = 0;
+	long i, j, ret = 0, locked_entries = 0, pageshift;
 	struct page *page = NULL;
 
 	mutex_lock(&mem_list_mutex);

@@ -166,6 +167,8 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		goto unlock_exit;
 	}
 

 > > +	mem->pageshift = 30; /* start from 1G pages - the biggest we have */          

quoted

What about 16G pages on an HPT system?        

Below in the loop mem->pageshift will reduce to the biggest actual size
which will be 16mb/64k/4k. Or remain 1GB if no memory is actually
pinned, no loss there.        

Are you saying that 16G IOMMU pages aren't supported?  Or that there's
some reason a guest can never use them?      

ah, 16_G_, not _M_. My bad. I just never tried such huge pages, I will
lift the limit up to 64 then, easier this way.    

Ah, no, rather this as the upper limit:

mem->pageshift = ilog2(entries) + PAGE_SHIFT;    

I can't make sense of this comment in context.  I see how you're
computing the minimum page size in the reserved region.

My question is about what the  is - the starting
value from which you calculate.  Currently it's 1G, but I can't
immediately see a reason that 16G is impossible here.  

16GB is impossible if the chunk we are preregistering here is smaller
than that, for example, the entire guest ram is 4GB.  

Of course.  Just like it was for 1GiB if you had a 512MiB guest, for
example.  I'm talking about a case where you have a guest that's

quoted

=16GiB and you *have* allocated 16GiB hugepages to back it.  

Then, assuming we are preregistering entire RAM as a single chunk, the
"maximum minimum" will be initialized as ">=16GiB" (but floor-aligned
to power of two) before the pinning loop and then reduce to the actual
page size, inside the loop. I feel like I am missing something in the
question, what is that?




--
Alexey

On Mon, Jul 02, 2018 at 04:32:27PM +1000, Alexey Kardashevskiy wrote:

On Mon, 2 Jul 2018 14:52:43 +1000
David Gibson [off-list ref] wrote:

quoted

On Mon, Jul 02, 2018 at 02:33:30PM +1000, Alexey Kardashevskiy wrote:

quoted

On Mon, 2 Jul 2018 14:08:52 +1000
David Gibson [off-list ref] wrote:
  

quoted

On Fri, Jun 29, 2018 at 05:07:47PM +1000, Alexey Kardashevskiy wrote:  

quoted

On Fri, 29 Jun 2018 15:18:20 +1000
Alexey Kardashevskiy [off-list ref] wrote:
    

quoted

On Fri, 29 Jun 2018 14:57:02 +1000
David Gibson [off-list ref] wrote:
    

quoted

On Fri, Jun 29, 2018 at 02:51:21PM +1000, Alexey Kardashevskiy wrote:      

quoted

On Fri, 29 Jun 2018 14:12:41 +1000
David Gibson [off-list ref] wrote:
        

quoted

On Tue, Jun 26, 2018 at 03:59:26PM +1000, Alexey Kardashevskiy wrote:        

quoted

We already have a check in drivers/vfio/vfio_iommu_spapr_tce.c that
an IOMMU page is contained in the physical page so the PCI hardware won't
get access to unassigned host memory.

However we do not have this check in KVM fastpath (H_PUT_TCE accelerated
code) so the user space can pin memory backed with 64k pages and create
a hardware TCE table with a bigger page size. We were lucky so far and
did not hit this yet as the very first time the mapping happens
we do not have tbl::it_userspace allocated yet and fall back to
the userspace which in turn calls VFIO IOMMU driver and that fails
because of the check in vfio_iommu_spapr_tce.c which is really
sustainable solution.

This stores the smallest preregistered page size in the preregistered
region descriptor and changes the mm_iommu_xxx API to check this against
the IOMMU page size.

Signed-off-by: Alexey Kardashevskiy <redacted>
---
Changes:
v2:
* explicitly check for compound pages before calling compound_order()

---
The bug is: run QEMU _without_ hugepages (no -mempath) and tell it to
advertise 16MB pages to the guest; a typical pseries guest will use 16MB
for IOMMU pages without checking the mmu pagesize and this will fail
at https://git.qemu.org/?p=qemu.git;a=blob;f=hw/vfio/common.c;h=fb396cf00ac40eb35967a04c9cc798ca896eed57;hb=refs/heads/master#l256

With the change, mapping will fail in KVM and the guest will print:

mlx5_core 0000:00:00.0: ibm,create-pe-dma-window(2027) 0 8000000 20000000 18 1f returned 0 (liobn = 0x80000001 starting addr = 8000000 0)
mlx5_core 0000:00:00.0: created tce table LIOBN 0x80000001 for /pci@800000020000000/ethernet@0
mlx5_core 0000:00:00.0: failed to map direct window for
/pci@800000020000000/ethernet@0: -1          

[snip]        

quoted

@@ -124,7 +125,7 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		struct mm_iommu_table_group_mem_t **pmem)
 {
 	struct mm_iommu_table_group_mem_t *mem;
-	long i, j, ret = 0, locked_entries = 0;
+	long i, j, ret = 0, locked_entries = 0, pageshift;
 	struct page *page = NULL;
 
 	mutex_lock(&mem_list_mutex);

@@ -166,6 +167,8 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 		goto unlock_exit;
 	}
 

 > > +	mem->pageshift = 30; /* start from 1G pages - the biggest we have */          

quoted

What about 16G pages on an HPT system?        

Below in the loop mem->pageshift will reduce to the biggest actual size
which will be 16mb/64k/4k. Or remain 1GB if no memory is actually
pinned, no loss there.        

Are you saying that 16G IOMMU pages aren't supported?  Or that there's
some reason a guest can never use them?      

ah, 16_G_, not _M_. My bad. I just never tried such huge pages, I will
lift the limit up to 64 then, easier this way.    

Ah, no, rather this as the upper limit:

mem->pageshift = ilog2(entries) + PAGE_SHIFT;    

I can't make sense of this comment in context.  I see how you're
computing the minimum page size in the reserved region.

My question is about what the  is - the starting
value from which you calculate.  Currently it's 1G, but I can't
immediately see a reason that 16G is impossible here.  

16GB is impossible if the chunk we are preregistering here is smaller
than that, for example, the entire guest ram is 4GB.  

Of course.  Just like it was for 1GiB if you had a 512MiB guest, for
example.  I'm talking about a case where you have a guest that's

quoted

=16GiB and you *have* allocated 16GiB hugepages to back it.  

Then, assuming we are preregistering entire RAM as a single chunk, the
"maximum minimum" will be initialized as ">=16GiB" (but floor-aligned
to power of two) before the pinning loop and then reduce to the actual
page size, inside the loop. I feel like I am missing something in the
question, what is that?

I wish I knew...

By the "maximum minimum" I'm talking about the shift value you start
with before you start looking at the actual pages.  Currently that is
exactly 30 (1 GiB).  AFAICT that prevents using 16GiB pages, and I
can't see a good reason for that.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson