On 2020-01-08 5:39 a.m., David Hildenbrand wrote:

On 07.01.20 21:59, Logan Gunthorpe wrote:

quoted

devm_memremap_pages() is currently used by the PCI P2PDMA code to create
struct page mappings for IO memory. At present, these mappings are created
with PAGE_KERNEL which implies setting the PAT bits to be WB. However, on
x86, an mtrr register will typically override this and force the cache
type to be UC-. In the case firmware doesn't set this register it is
effectively WB and will typically result in a machine check exception
when it's accessed.

Other arches are not currently likely to function correctly seeing they
don't have any MTRR registers to fall back on.

To solve this, add an argument to arch_add_memory() to explicitly
set the pgprot value to a specific value.

You're adding a parameter indirectly by adding it to the structure.
Maybe "provide a way to specify the pgprot value explicitly to
arch_add_memory()"

quoted

Of the arches that support MEMORY_HOTPLUG: x86_64, s390 and arm64 is a

s/is/need/

quoted

simple change to pass the pgprot_t down to their respective functions
which set up the page tables. For x86_32, set the page tables explicitly

"page table protection" ?

quoted

using _set_memory_prot() (seeing they are already mapped). For sh, reject
anything but PAGE_KERNEL settings -- this should be fine, for now, seeing
sh doesn't support ZONE_DEVICE anyway.

Cc: Dan Williams <redacted>
Cc: David Hildenbrand <redacted>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
 arch/arm64/mm/mmu.c            | 3 ++-
 arch/ia64/mm/init.c            | 4 ++++
 arch/powerpc/mm/mem.c          | 3 ++-
 arch/s390/mm/init.c            | 2 +-
 arch/sh/mm/init.c              | 3 +++
 arch/x86/mm/init_32.c          | 5 +++++
 arch/x86/mm/init_64.c          | 2 +-
 include/linux/memory_hotplug.h | 2 ++
 mm/memory_hotplug.c            | 2 +-
 mm/memremap.c                  | 6 +++---
 10 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 3320406579c3..9b214b0d268f 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c

@@ -1058,7 +1058,8 @@ int arch_add_memory(int nid, u64 start, u64 size,
 		flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
 
 	__create_pgd_mapping(swapper_pg_dir, start, __phys_to_virt(start),
-			     size, PAGE_KERNEL, __pgd_pgtable_alloc, flags);
+			     size, modifiers->pgprot, __pgd_pgtable_alloc,
+			     flags);
 
 	memblock_clear_nomap(start, size);
 

diff --git a/arch/ia64/mm/init.c b/arch/ia64/mm/init.c
index daf438e08b96..5fd6ae4929c9 100644
--- a/arch/ia64/mm/init.c
+++ b/arch/ia64/mm/init.c

@@ -677,6 +677,10 @@ int arch_add_memory(int nid, u64 start, u64 size,
 	int ret;
 
 	ret = __add_pages(nid, start_pfn, nr_pages, modifiers);
+	if (modifiers->pgprot != PAGE_KERNEL)
+		return -EINVAL;

... maybe better "if (WARN_ON_ONCE(...))"
[...]

quoted

--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h

@@ -56,9 +56,11 @@ enum {
 /*
  * Restrictions for the memory hotplug:
  * altmap: alternative allocator for memmap array
+ * pgprot: page protection flags to apply to newly added page tables
  */
 struct mhp_modifiers {
 	struct vmem_altmap *altmap;
+	pgprot_t pgprot;
 };
 
 /*

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 1bb3f92e087d..0888f821af06 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c

@@ -1027,7 +1027,7 @@ static int online_memory_block(struct memory_block *mem, void *arg)
  */
 int __ref add_memory_resource(int nid, struct resource *res)
 {
-	struct mhp_modifiers modifiers = {};
+	struct mhp_modifiers modifiers = {.pgprot = PAGE_KERNEL};

I think we usually use spaces like

= { .pgprot = PAGE_KERNEL };

t480s: ~/git/linux virtio-mem-v1 $ git grep "= {\." | wc -l
978
t480s: ~/git/linux virtio-mem-v1 $ git grep "= { " | wc -l
35447

quoted

 	u64 start, size;
 	bool new_node = false;
 	int ret;

diff --git a/mm/memremap.c b/mm/memremap.c
index e30be8ba706b..45ab4ef0643d 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c

@@ -163,8 +163,8 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
 		 * We do not want any optional features only our own memmap
 		 */
 		.altmap = pgmap_altmap(pgmap),
+		.pgprot = PAGE_KERNEL,
 	};
-	pgprot_t pgprot = PAGE_KERNEL;
 	int error, is_ram;
 	bool need_devmap_managed = true;
 

@@ -252,8 +252,8 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
 	if (nid < 0)
 		nid = numa_mem_id();
 
-	error = track_pfn_remap(NULL, &pgprot, PHYS_PFN(res->start), 0,
-			resource_size(res));
+	error = track_pfn_remap(NULL, &modifiers.pgprot, PHYS_PFN(res->start),
+				0, resource_size(res));
 	if (error)
 		goto err_pfn_remap;
 

The !arch code looks good to me (besides I would prefer "params" instead
of "modifiers").

Acked-by: David Hildenbrand <redacted>

Thanks, I'll make the changes above for v3.

Logan