[PATCH v3 6/7] mm/memory_hotplug: Add pgprot_t to mhp_params

[Logan Gunthorpe]

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, provide a way to specify the pgprot value explicitly to
arch_add_memory().

Of the arches that support MEMORY_HOTPLUG: x86_64, and arm64 need a 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 using
_set_memory_prot() (seeing they are already mapped). For ia64, s390 and
sh, reject anything but PAGE_KERNEL settings -- this should be fine,
for now, seeing these architectures don't support ZONE_DEVICE.

A check in __add_pages() is also added to ensure the pgprot parameter was
set for all arches.

Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
---
 arch/arm64/mm/mmu.c            | 3 ++-
 arch/ia64/mm/init.c            | 3 +++
 arch/powerpc/mm/mem.c          | 3 ++-
 arch/s390/mm/init.c            | 3 +++
 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            | 5 ++++-
 mm/memremap.c                  | 6 +++---
 10 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index ee37bca8aba8..ea3fa844a8a2 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, params->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 97bbc23ea1e3..d637b4ea3147 100644
--- a/arch/ia64/mm/init.c
+++ b/arch/ia64/mm/init.c
@@ -676,6 +676,9 @@ int arch_add_memory(int nid, u64 start, u64 size,
 	unsigned long nr_pages = size >> PAGE_SHIFT;
 	int ret;
 
+	if (WARN_ON_ONCE(params->pgprot.pgprot != PAGE_KERNEL.pgprot))
+		return -EINVAL;
+
 	ret = __add_pages(nid, start_pfn, nr_pages, params);
 	if (ret)
 		printk("%s: Problem encountered in __add_pages() as ret=%d\n",
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 19b1da5d7eca..832412bc7fad 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -138,7 +138,8 @@ int __ref arch_add_memory(int nid, u64 start, u64 size,
 	resize_hpt_for_hotplug(memblock_phys_mem_size());
 
 	start = (unsigned long)__va(start);
-	rc = create_section_mapping(start, start + size, nid, PAGE_KERNEL);
+	rc = create_section_mapping(start, start + size, nid,
+				    params->pgprot);
 	if (rc) {
 		pr_warn("Unable to create mapping for hot added memory 0x%llx..0x%llx: %d\n",
 			start, start + size, rc);
diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index e9e4a7abd0cc..87b2d024e75a 100644
--- a/arch/s390/mm/init.c
+++ b/arch/s390/mm/init.c
@@ -277,6 +277,9 @@ int arch_add_memory(int nid, u64 start, u64 size,
 	if (WARN_ON_ONCE(params->altmap))
 		return -EINVAL;
 
+	if (WARN_ON_ONCE(params->pgprot.pgprot != PAGE_KERNEL.pgprot))
+		return -EINVAL;
+
 	rc = vmem_add_mapping(start, size);
 	if (rc)
 		return rc;
diff --git a/arch/sh/mm/init.c b/arch/sh/mm/init.c
index e5114c053364..b9de2d4fa57e 100644
--- a/arch/sh/mm/init.c
+++ b/arch/sh/mm/init.c
@@ -412,6 +412,9 @@ int arch_add_memory(int nid, u64 start, u64 size,
 	unsigned long nr_pages = size >> PAGE_SHIFT;
 	int ret;
 
+	if (WARN_ON_ONCE(params->pgprot.pgprot != PAGE_KERNEL.pgprot)
+		return -EINVAL;
+
 	/* We only have ZONE_NORMAL, so this is easy.. */
 	ret = __add_pages(nid, start_pfn, nr_pages, params);
 	if (unlikely(ret))
diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
index e25a4218e6ff..96d8e4fb1cc8 100644
--- a/arch/x86/mm/init_32.c
+++ b/arch/x86/mm/init_32.c
@@ -858,6 +858,11 @@ int arch_add_memory(int nid, u64 start, u64 size,
 {
 	unsigned long start_pfn = start >> PAGE_SHIFT;
 	unsigned long nr_pages = size >> PAGE_SHIFT;
+	int ret;
+
+	ret = _set_memory_prot(start, nr_pages, params->pgprot);
+	if (ret)
+		return ret;
 
 	return __add_pages(nid, start_pfn, nr_pages, params);
 }
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 9e7692080dda..230240af38b4 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -868,7 +868,7 @@ int arch_add_memory(int nid, u64 start, u64 size,
 	unsigned long start_pfn = start >> PAGE_SHIFT;
 	unsigned long nr_pages = size >> PAGE_SHIFT;
 
-	init_memory_mapping(start, start + size, PAGE_KERNEL);
+	init_memory_mapping(start, start + size, params->pgprot);
 
 	return add_pages(nid, start_pfn, nr_pages, params);
 }
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index c5df1b3dada0..30d6c1b8847e 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -56,9 +56,11 @@ enum {
 /*
  * Extended parameters for memory hotplug:
  * altmap: alternative allocator for memmap array (optional)
+ * pgprot: page protection flags to apply to newly added page tables (required)
  */
 struct mhp_params {
 	struct vmem_altmap *altmap;
+	pgprot_t pgprot;
 };
 
 /*
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index c69469e1b40e..d7d4806ad81b 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -305,6 +305,9 @@ int __ref __add_pages(int nid, unsigned long pfn, unsigned long nr_pages,
 	unsigned long nr, start_sec, end_sec;
 	struct vmem_altmap *altmap = params->altmap;
 
+	if (WARN_ON_ONCE(!params->pgprot.pgprot))
+		return -EINVAL;
+
 	err = check_hotplug_memory_addressable(pfn, nr_pages);
 	if (err)
 		return err;
@@ -993,7 +996,7 @@ static int online_memory_block(struct memory_block *mem, void *arg)
  */
 int __ref add_memory_resource(int nid, struct resource *res)
 {
-	struct mhp_params params = {};
+	struct mhp_params params = { .pgprot = PAGE_KERNEL };
 	u64 start, size;
 	bool new_node = false;
 	int ret;
diff --git a/mm/memremap.c b/mm/memremap.c
index 6891a503a078..06742372a203 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -166,8 +166,8 @@ 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;
 
@@ -255,8 +255,8 @@ 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, &params.pgprot, PHYS_PFN(res->start),
+				0, resource_size(res));
 	if (error)
 		goto err_pfn_remap;
 
-- 
2.20.1