[RFC PATCH kernel] KVM: PPC: Book3S PR: Fix WIMG handling under pHyp

96df226 "KVM: PPC: Book3S PR: Preserve storage control bits" added WIMG
bits preserving but it missed 2 special cases:
- a magic page in kvmppc_mmu_book3s_64_xlate() and
- guest real mode in kvmppc_handle_pagefault().

For these ptes WIMG were 0 and pHyp failed on these causing a guest to
stop in the very beginning at NIP=0x100 (due to bd9166ffe
"KVM: PPC: Book3S PR: Exit KVM on failed mapping").

This initializes WIMG to non-zero value HPTE_R_M. The value is chosen
as (0x192 & HPTE_R_WIMG); 0x192 is a magic value from
kvmppc_mmu_map_page().

Fixes: 96df226 "KVM: PPC: Book3S PR: Preserve storage control bits"
Signed-off-by: Alexey Kardashevskiy <redacted>
---

This indeed fixes PR KVM + VFIO under pHyp but selection of HPTE_R_M
is arguable.

---
 arch/powerpc/kvm/book3s_64_mmu.c | 1 +
 arch/powerpc/kvm/book3s_pr.c     | 1 +
 2 files changed, 2 insertions(+)

diff --git a/arch/powerpc/kvm/book3s_64_mmu.c b/arch/powerpc/kvm/book3s_64_mmu.c
index 29ebe2f..a93d719 100644
--- a/arch/powerpc/kvm/book3s_64_mmu.c
+++ b/arch/powerpc/kvm/book3s_64_mmu.c

@@ -235,6 +235,7 @@ static int kvmppc_mmu_book3s_64_xlate(struct kvm_vcpu *vcpu, gva_t eaddr,
 		gpte->may_read = true;
 		gpte->may_write = true;
 		gpte->page_size = MMU_PAGE_4K;
+		gpte->wimg = HPTE_R_M;
 
 		return 0;
 	}

diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
index 69a0944..0152efe 100644
--- a/arch/powerpc/kvm/book3s_pr.c
+++ b/arch/powerpc/kvm/book3s_pr.c

@@ -557,6 +557,7 @@ int kvmppc_handle_pagefault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 		pte.eaddr = eaddr;
 		pte.vpage = eaddr >> 12;
 		pte.page_size = MMU_PAGE_64K;
+		pte.wimg = HPTE_R_M;
 	}
 
 	switch (kvmppc_get_msr(vcpu) & (MSR_DR|MSR_IR)) {

-- 
2.11.0

On 22.11.17 04:42, Alexey Kardashevskiy wrote:

96df226 "KVM: PPC: Book3S PR: Preserve storage control bits" added WIMG
bits preserving but it missed 2 special cases:
- a magic page in kvmppc_mmu_book3s_64_xlate() and
- guest real mode in kvmppc_handle_pagefault().

For these ptes WIMG were 0 and pHyp failed on these causing a guest to
stop in the very beginning at NIP=0x100 (due to bd9166ffe
"KVM: PPC: Book3S PR: Exit KVM on failed mapping").

This initializes WIMG to non-zero value HPTE_R_M. The value is chosen
as (0x192 & HPTE_R_WIMG); 0x192 is a magic value from
kvmppc_mmu_map_page().

Fixes: 96df226 "KVM: PPC: Book3S PR: Preserve storage control bits"
Signed-off-by: Alexey Kardashevskiy <redacted>
---

This indeed fixes PR KVM + VFIO under pHyp but selection of HPTE_R_M
is arguable.

This does indeed fix the breakage we've seen:

Tested-by: Ruediger Oertel <redacted>


Alex

On Wed, 22 Nov 2017 14:42:21 +1100
Alexey Kardashevskiy [off-list ref] wrote:

96df226 "KVM: PPC: Book3S PR: Preserve storage control bits" added WIMG
bits preserving but it missed 2 special cases:
- a magic page in kvmppc_mmu_book3s_64_xlate() and
- guest real mode in kvmppc_handle_pagefault().

For these ptes WIMG were 0 and pHyp failed on these causing a guest to
stop in the very beginning at NIP=0x100 (due to bd9166ffe
"KVM: PPC: Book3S PR: Exit KVM on failed mapping").

This initializes WIMG to non-zero value HPTE_R_M. The value is chosen
as (0x192 & HPTE_R_WIMG); 0x192 is a magic value from
kvmppc_mmu_map_page().

Fixes: 96df226 "KVM: PPC: Book3S PR: Preserve storage control bits"
Signed-off-by: Alexey Kardashevskiy <redacted>
---

This indeed fixes PR KVM + VFIO under pHyp but selection of HPTE_R_M
is arguable.

The initial page fault at 0x100 on machine startup causes H_ENTER to fail in
pHyp with H_PARAMETER, as described in PAPR:

 The hypervisor checks that the WIMG bits within the PTE are appropriate for the
 physical page number else H_Parameter return. (For System Memory pages WIMG=0010,
 or, 1110 if the SAO option is enabled, and for IO pages WIMG=01**.)

I'm not aware we care for SAO so HPTE_R_M looks like the only sensible choice,
or I'm missing something ?

Anyway, this patch allows to start a PR guest on PowerVM again.

Reviewed-by: Greg Kurz <redacted>

and

Tested-by: Greg Kurz <redacted>

On 24.11.17 00:33, Greg Kurz wrote:

On Wed, 22 Nov 2017 14:42:21 +1100
Alexey Kardashevskiy [off-list ref] wrote:

quoted

96df226 "KVM: PPC: Book3S PR: Preserve storage control bits" added WIMG
bits preserving but it missed 2 special cases:
- a magic page in kvmppc_mmu_book3s_64_xlate() and
- guest real mode in kvmppc_handle_pagefault().

For these ptes WIMG were 0 and pHyp failed on these causing a guest to
stop in the very beginning at NIP=0x100 (due to bd9166ffe
"KVM: PPC: Book3S PR: Exit KVM on failed mapping").

This initializes WIMG to non-zero value HPTE_R_M. The value is chosen
as (0x192 & HPTE_R_WIMG); 0x192 is a magic value from
kvmppc_mmu_map_page().

Fixes: 96df226 "KVM: PPC: Book3S PR: Preserve storage control bits"
Signed-off-by: Alexey Kardashevskiy <redacted>
---

This indeed fixes PR KVM + VFIO under pHyp but selection of HPTE_R_M
is arguable.

The initial page fault at 0x100 on machine startup causes H_ENTER to fail in
pHyp with H_PARAMETER, as described in PAPR:

 The hypervisor checks that the WIMG bits within the PTE are appropriate for the
 physical page number else H_Parameter return. (For System Memory pages WIMG=0010,
 or, 1110 if the SAO option is enabled, and for IO pages WIMG=01**.)

I'm not aware we care for SAO so HPTE_R_M looks like the only sensible choice,
or I'm missing something ?

Anyway, this patch allows to start a PR guest on PowerVM again.

Reviewed-by: Greg Kurz <redacted>

and

Tested-by: Greg Kurz <redacted>

So doesn't that mean we should pick it up, mark it CC stable and push it
upstream?


Alex

Paul,


I saw comments about the commit log but did this go to any tree eventually?


On 22/11/17 14:42, Alexey Kardashevskiy wrote:

-- 
Alexey

On Wed, Nov 22, 2017 at 02:42:21PM +1100, Alexey Kardashevskiy wrote:

96df226 "KVM: PPC: Book3S PR: Preserve storage control bits" added WIMG
bits preserving but it missed 2 special cases:
- a magic page in kvmppc_mmu_book3s_64_xlate() and
- guest real mode in kvmppc_handle_pagefault().

For these ptes WIMG were 0 and pHyp failed on these causing a guest to
stop in the very beginning at NIP=0x100 (due to bd9166ffe
"KVM: PPC: Book3S PR: Exit KVM on failed mapping").

This initializes WIMG to non-zero value HPTE_R_M. The value is chosen
as (0x192 & HPTE_R_WIMG); 0x192 is a magic value from
kvmppc_mmu_map_page().

Fixes: 96df226 "KVM: PPC: Book3S PR: Preserve storage control bits"
Signed-off-by: Alexey Kardashevskiy <redacted>

Thanks, applied to my kvm-ppc-fixes branch, with an updated commit
message, fixes: tag, and cc:stable@vger.kernel.org.

Paul.