[PATCH 0/2] mm: protection_map[] cleanups

[PATCH 0/2] mm: protection_map[] cleanups

[Anshuman Khandual]

This is a split series from an earlier work which tried to drop the array
protection_map[] on various platforms. This series applies on v5.18-rc1.

https://lore.kernel.org/all/1646045273-9343-1-git-send-email-anshuman.khandual@arm.com/

Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andrew Morton <akpm@linux-foundation.org>

Anshuman Khandual (2):
  mm/debug_vm_pgtable: Drop protection_map[] usage
  mm/mmap: Clarify protection_map[] indices

 mm/debug_vm_pgtable.c | 31 +++++++++++++++++++------------
 mm/mmap.c             | 18 ++++++++++++++++--
 2 files changed, 35 insertions(+), 14 deletions(-)

-- 
2.25.1

[PATCH 1/2] mm/debug_vm_pgtable: Drop protection_map[] usage

[Anshuman Khandual]

Although protection_map[] contains the platform defined page protection map
for a given vm_flags combination, vm_get_page_prot() is the right interface
to use. This will also reduce dependency on protection_map[] which is going
to be dropped off completely later on.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
 mm/debug_vm_pgtable.c | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index db2abd9e415b..30fd11a2ed32 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -93,7 +93,7 @@ struct pgtable_debug_args {
 
 static void __init pte_basic_tests(struct pgtable_debug_args *args, int idx)
 {
-	pgprot_t prot = protection_map[idx];
+	pgprot_t prot = vm_get_page_prot(idx);
 	pte_t pte = pfn_pte(args->fixed_pte_pfn, prot);
 	unsigned long val = idx, *ptr = &val;
 
@@ -101,7 +101,7 @@ static void __init pte_basic_tests(struct pgtable_debug_args *args, int idx)
 
 	/*
 	 * This test needs to be executed after the given page table entry
-	 * is created with pfn_pte() to make sure that protection_map[idx]
+	 * is created with pfn_pte() to make sure that vm_get_page_prot(idx)
 	 * does not have the dirty bit enabled from the beginning. This is
 	 * important for platforms like arm64 where (!PTE_RDONLY) indicate
 	 * dirty bit being set.
@@ -190,7 +190,7 @@ static void __init pte_savedwrite_tests(struct pgtable_debug_args *args)
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 static void __init pmd_basic_tests(struct pgtable_debug_args *args, int idx)
 {
-	pgprot_t prot = protection_map[idx];
+	pgprot_t prot = vm_get_page_prot(idx);
 	unsigned long val = idx, *ptr = &val;
 	pmd_t pmd;
 
@@ -202,7 +202,7 @@ static void __init pmd_basic_tests(struct pgtable_debug_args *args, int idx)
 
 	/*
 	 * This test needs to be executed after the given page table entry
-	 * is created with pfn_pmd() to make sure that protection_map[idx]
+	 * is created with pfn_pmd() to make sure that vm_get_page_prot(idx)
 	 * does not have the dirty bit enabled from the beginning. This is
 	 * important for platforms like arm64 where (!PTE_RDONLY) indicate
 	 * dirty bit being set.
@@ -325,7 +325,7 @@ static void __init pmd_savedwrite_tests(struct pgtable_debug_args *args)
 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 static void __init pud_basic_tests(struct pgtable_debug_args *args, int idx)
 {
-	pgprot_t prot = protection_map[idx];
+	pgprot_t prot = vm_get_page_prot(idx);
 	unsigned long val = idx, *ptr = &val;
 	pud_t pud;
 
@@ -337,7 +337,7 @@ static void __init pud_basic_tests(struct pgtable_debug_args *args, int idx)
 
 	/*
 	 * This test needs to be executed after the given page table entry
-	 * is created with pfn_pud() to make sure that protection_map[idx]
+	 * is created with pfn_pud() to make sure that vm_get_page_prot(idx)
 	 * does not have the dirty bit enabled from the beginning. This is
 	 * important for platforms like arm64 where (!PTE_RDONLY) indicate
 	 * dirty bit being set.
@@ -1106,14 +1106,14 @@ static int __init init_args(struct pgtable_debug_args *args)
 	/*
 	 * Initialize the debugging data.
 	 *
-	 * protection_map[0] (or even protection_map[8]) will help create
-	 * page table entries with PROT_NONE permission as required for
-	 * pxx_protnone_tests().
+	 * vm_get_page_prot(VM_NONE) or vm_get_page_prot(VM_SHARED|VM_NONE)
+	 * will help create page table entries with PROT_NONE permission as
+	 * required for pxx_protnone_tests().
 	 */
 	memset(args, 0, sizeof(*args));
 	args->vaddr              = get_random_vaddr();
 	args->page_prot          = vm_get_page_prot(VMFLAGS);
-	args->page_prot_none     = protection_map[0];
+	args->page_prot_none     = vm_get_page_prot(VM_NONE);
 	args->is_contiguous_page = false;
 	args->pud_pfn            = ULONG_MAX;
 	args->pmd_pfn            = ULONG_MAX;
@@ -1248,12 +1248,19 @@ static int __init debug_vm_pgtable(void)
 		return ret;
 
 	/*
-	 * Iterate over the protection_map[] to make sure that all
+	 * Iterate over each possible vm_flags to make sure that all
 	 * the basic page table transformation validations just hold
 	 * true irrespective of the starting protection value for a
 	 * given page table entry.
+	 *
+	 * Protection based vm_flags combinatins are always linear
+	 * and increasing i.e starting from VM_NONE and going upto
+	 * (VM_SHARED | READ | WRITE | EXEC).
 	 */
-	for (idx = 0; idx < ARRAY_SIZE(protection_map); idx++) {
+#define VM_FLAGS_START	(VM_NONE)
+#define VM_FLAGS_END	(VM_SHARED | VM_EXEC | VM_WRITE | VM_READ)
+
+	for (idx = VM_FLAGS_START; idx <= VM_FLAGS_END; idx++) {
 		pte_basic_tests(&args, idx);
 		pmd_basic_tests(&args, idx);
 		pud_basic_tests(&args, idx);
-- 
2.25.1

[PATCH 2/2] mm/mmap: Clarify protection_map[] indices

[Anshuman Khandual]

protection_map[] maps vm_flags access combinations into page protection
value as defined by the platform via __PXXX and __SXXX macros. The array
indices in protection_map[], represents vm_flags access combinations but
it's not very intuitive to derive. This makes it clear and explicit.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
 mm/mmap.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 3aa839f81e63..4b8ee3fd03ad 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -102,8 +102,22 @@ static void unmap_region(struct mm_struct *mm,
  *								x: (yes) yes
  */
 pgprot_t protection_map[16] __ro_after_init = {
-	__P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111,
-	__S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
+	[VM_NONE]					= __P000,
+	[VM_READ]					= __P001,
+	[VM_WRITE]					= __P010,
+	[VM_WRITE | VM_READ]				= __P011,
+	[VM_EXEC]					= __P100,
+	[VM_EXEC | VM_READ]				= __P101,
+	[VM_EXEC | VM_WRITE]				= __P110,
+	[VM_EXEC | VM_WRITE | VM_READ]			= __P111,
+	[VM_SHARED]					= __S000,
+	[VM_SHARED | VM_READ]				= __S001,
+	[VM_SHARED | VM_WRITE]				= __S010,
+	[VM_SHARED | VM_WRITE | VM_READ]		= __S011,
+	[VM_SHARED | VM_EXEC]				= __S100,
+	[VM_SHARED | VM_EXEC | VM_READ]			= __S101,
+	[VM_SHARED | VM_EXEC | VM_WRITE]		= __S110,
+	[VM_SHARED | VM_EXEC | VM_WRITE | VM_READ]	= __S111
 };
 
 #ifndef CONFIG_ARCH_HAS_FILTER_PGPROT
-- 
2.25.1

Re: [PATCH 1/2] mm/debug_vm_pgtable: Drop protection_map[] usage

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH 2/2] mm/mmap: Clarify protection_map[] indices

[Christoph Hellwig]

On Mon, Apr 04, 2022 at 08:48:40AM +0530, Anshuman Khandual wrote:
> protection_map[] maps vm_flags access combinations into page protection
> value as defined by the platform via __PXXX and __SXXX macros. The array
> indices in protection_map[], represents vm_flags access combinations but
> it's not very intuitive to derive. This makes it clear and explicit.

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>