[PATCH V3 0/2] mm/debug_vm_pgtable: Some minor updates

[PATCH V3 0/2] mm/debug_vm_pgtable: Some minor updates

[Anshuman Khandual]

This series contains some cleanups and new test suggestions from Catalin
from an earlier discussion.

https://lore.kernel.org/linux-mm/20201123142237.GF17833@gaia/

This series is based on v5.11-rc4 and has been tested on arm64, s390 and x86
but has only been build tested on riscv, arc etc. It would be great if folks
could test this on these platforms as well. Thank you.

Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Andrew Morton <akpm@linux-foundation.org>

Changes in V3:

- Modified the comments for pxx_dirty(pxx_wrprotect(pxx)) tests per Steven
 
Changes in V2:

https://lore.kernel.org/linux-mm/1606825169-5229-1-git-send-email-anshuman.khandual@arm.com/

- Added some missing tests in pud_basic_tests()
- Added bidirectional dirty check after pxx_wrprotect() per Catalin
- Moved WARN_ON(pte_dirty(pte_wrprotect(pte))) just after page table entry creation

Changes in V1:

https://lore.kernel.org/linux-mm/1606453584-15399-1-git-send-email-anshuman.khandual@arm.com/

Anshuman Khandual (2):
  mm/debug_vm_pgtable/basic: Add validation for dirtiness after write protect
  mm/debug_vm_pgtable/basic: Iterate over entire protection_map[]

 Documentation/vm/arch_pgtable_helpers.rst |  8 +--
 mm/debug_vm_pgtable.c                     | 86 +++++++++++++++++++----
 2 files changed, 78 insertions(+), 16 deletions(-)

-- 
2.20.1

[PATCH V3 1/2] mm/debug_vm_pgtable/basic: Add validation for dirtiness after write protect

[Anshuman Khandual]

This adds validation tests for dirtiness after write protect conversion for
each page table level. There are two new separate test types involved here.

The first test ensures that a given page table entry does not become dirty
after pxx_wrprotect(). This is important for platforms like arm64 which
transfers and drops the hardware dirty bit (!PTE_RDONLY) to the software
dirty bit while making it an write protected one. This test ensures that
no fresh page table entry could be created with hardware dirty bit set.
The second test ensures that a given page table entry always preserve the
dirty information across pxx_wrprotect().

This adds two previously missing PUD level basic tests and while here fixes
pxx_wrprotect() related typos in the documentation file.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Tested-by: Gerald Schaefer <gerald.schaefer@de.ibm.com> [s390]
Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
 Documentation/vm/arch_pgtable_helpers.rst |  8 ++---
 mm/debug_vm_pgtable.c                     | 39 +++++++++++++++++++++++
 2 files changed, 43 insertions(+), 4 deletions(-)

diff --git a/Documentation/vm/arch_pgtable_helpers.rst b/Documentation/vm/arch_pgtable_helpers.rst
index f3591ee3aaa8..552567d863b8 100644
--- a/Documentation/vm/arch_pgtable_helpers.rst
+++ b/Documentation/vm/arch_pgtable_helpers.rst
@@ -50,7 +50,7 @@ PTE Page Table Helpers
 +---------------------------+--------------------------------------------------+
 | pte_mkwrite               | Creates a writable PTE                           |
 +---------------------------+--------------------------------------------------+
-| pte_mkwrprotect           | Creates a write protected PTE                    |
+| pte_wrprotect             | Creates a write protected PTE                    |
 +---------------------------+--------------------------------------------------+
 | pte_mkspecial             | Creates a special PTE                            |
 +---------------------------+--------------------------------------------------+
@@ -120,7 +120,7 @@ PMD Page Table Helpers
 +---------------------------+--------------------------------------------------+
 | pmd_mkwrite               | Creates a writable PMD                           |
 +---------------------------+--------------------------------------------------+
-| pmd_mkwrprotect           | Creates a write protected PMD                    |
+| pmd_wrprotect             | Creates a write protected PMD                    |
 +---------------------------+--------------------------------------------------+
 | pmd_mkspecial             | Creates a special PMD                            |
 +---------------------------+--------------------------------------------------+
@@ -186,7 +186,7 @@ PUD Page Table Helpers
 +---------------------------+--------------------------------------------------+
 | pud_mkwrite               | Creates a writable PUD                           |
 +---------------------------+--------------------------------------------------+
-| pud_mkwrprotect           | Creates a write protected PUD                    |
+| pud_wrprotect             | Creates a write protected PUD                    |
 +---------------------------+--------------------------------------------------+
 | pud_mkdevmap              | Creates a ZONE_DEVICE mapped PUD                 |
 +---------------------------+--------------------------------------------------+
@@ -224,7 +224,7 @@ HugeTLB Page Table Helpers
 +---------------------------+--------------------------------------------------+
 | huge_pte_mkwrite          | Creates a writable HugeTLB                       |
 +---------------------------+--------------------------------------------------+
-| huge_pte_mkwrprotect      | Creates a write protected HugeTLB                |
+| huge_pte_wrprotect        | Creates a write protected HugeTLB                |
 +---------------------------+--------------------------------------------------+
 | huge_ptep_get_and_clear   | Clears a HugeTLB                                 |
 +---------------------------+--------------------------------------------------+
diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index c05d9dcf7891..1842d97522bb 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -63,6 +63,16 @@ static void __init pte_basic_tests(unsigned long pfn, pgprot_t prot)
 	pte_t pte = pfn_pte(pfn, prot);
 
 	pr_debug("Validating PTE basic\n");
+
+	/*
+	 * This test needs to be executed after the given page table entry
+	 * is created with pfn_pte() to make sure that protection_map[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.
+	 */
+	WARN_ON(pte_dirty(pte_wrprotect(pte)));
+
 	WARN_ON(!pte_same(pte, pte));
 	WARN_ON(!pte_young(pte_mkyoung(pte_mkold(pte))));
 	WARN_ON(!pte_dirty(pte_mkdirty(pte_mkclean(pte))));
@@ -70,6 +80,8 @@ static void __init pte_basic_tests(unsigned long pfn, pgprot_t prot)
 	WARN_ON(pte_young(pte_mkold(pte_mkyoung(pte))));
 	WARN_ON(pte_dirty(pte_mkclean(pte_mkdirty(pte))));
 	WARN_ON(pte_write(pte_wrprotect(pte_mkwrite(pte))));
+	WARN_ON(pte_dirty(pte_wrprotect(pte_mkclean(pte))));
+	WARN_ON(!pte_dirty(pte_wrprotect(pte_mkdirty(pte))));
 }
 
 static void __init pte_advanced_tests(struct mm_struct *mm,
@@ -137,6 +149,17 @@ static void __init pmd_basic_tests(unsigned long pfn, pgprot_t prot)
 		return;
 
 	pr_debug("Validating PMD basic\n");
+
+	/*
+	 * This test needs to be executed after the given page table entry
+	 * is created with pfn_pmd() to make sure that protection_map[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.
+	 */
+	WARN_ON(pmd_dirty(pmd_wrprotect(pmd)));
+
+
 	WARN_ON(!pmd_same(pmd, pmd));
 	WARN_ON(!pmd_young(pmd_mkyoung(pmd_mkold(pmd))));
 	WARN_ON(!pmd_dirty(pmd_mkdirty(pmd_mkclean(pmd))));
@@ -144,6 +167,8 @@ static void __init pmd_basic_tests(unsigned long pfn, pgprot_t prot)
 	WARN_ON(pmd_young(pmd_mkold(pmd_mkyoung(pmd))));
 	WARN_ON(pmd_dirty(pmd_mkclean(pmd_mkdirty(pmd))));
 	WARN_ON(pmd_write(pmd_wrprotect(pmd_mkwrite(pmd))));
+	WARN_ON(pmd_dirty(pmd_wrprotect(pmd_mkclean(pmd))));
+	WARN_ON(!pmd_dirty(pmd_wrprotect(pmd_mkdirty(pmd))));
 	/*
 	 * A huge page does not point to next level page table
 	 * entry. Hence this must qualify as pmd_bad().
@@ -257,11 +282,25 @@ static void __init pud_basic_tests(unsigned long pfn, pgprot_t prot)
 		return;
 
 	pr_debug("Validating PUD basic\n");
+
+	/*
+	 * This test needs to be executed after the given page table entry
+	 * is created with pfn_pud() to make sure that protection_map[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.
+	 */
+	WARN_ON(pud_dirty(pud_wrprotect(pud)));
+
 	WARN_ON(!pud_same(pud, pud));
 	WARN_ON(!pud_young(pud_mkyoung(pud_mkold(pud))));
+	WARN_ON(!pud_dirty(pud_mkdirty(pud_mkclean(pud))));
+	WARN_ON(pud_dirty(pud_mkclean(pud_mkdirty(pud))));
 	WARN_ON(!pud_write(pud_mkwrite(pud_wrprotect(pud))));
 	WARN_ON(pud_write(pud_wrprotect(pud_mkwrite(pud))));
 	WARN_ON(pud_young(pud_mkold(pud_mkyoung(pud))));
+	WARN_ON(pud_dirty(pud_wrprotect(pud_mkclean(pud))));
+	WARN_ON(!pud_dirty(pud_wrprotect(pud_mkdirty(pud))));
 
 	if (mm_pmd_folded(mm))
 		return;
-- 
2.20.1

[PATCH V3 2/2] mm/debug_vm_pgtable/basic: Iterate over entire protection_map[]

[Anshuman Khandual]

Currently the basic tests just validate various page table transformations
after starting with vm_get_page_prot(VM_READ|VM_WRITE|VM_EXEC) protection.
Instead scan over the entire protection_map[] for better coverage. It also
makes sure that all these basic page table tranformations checks hold true
irrespective of the starting protection value for the page table entry.
There is also a slight change in the debug print format for basic tests to
capture the protection value it is being tested with. The modified output
looks something like

[pte_basic_tests          ]: Validating PTE basic ()
[pte_basic_tests          ]: Validating PTE basic (read)
[pte_basic_tests          ]: Validating PTE basic (write)
[pte_basic_tests          ]: Validating PTE basic (read|write)
[pte_basic_tests          ]: Validating PTE basic (exec)
[pte_basic_tests          ]: Validating PTE basic (read|exec)
[pte_basic_tests          ]: Validating PTE basic (write|exec)
[pte_basic_tests          ]: Validating PTE basic (read|write|exec)
[pte_basic_tests          ]: Validating PTE basic (shared)
[pte_basic_tests          ]: Validating PTE basic (read|shared)
[pte_basic_tests          ]: Validating PTE basic (write|shared)
[pte_basic_tests          ]: Validating PTE basic (read|write|shared)
[pte_basic_tests          ]: Validating PTE basic (exec|shared)
[pte_basic_tests          ]: Validating PTE basic (read|exec|shared)
[pte_basic_tests          ]: Validating PTE basic (write|exec|shared)
[pte_basic_tests          ]: Validating PTE basic (read|write|exec|shared)

This adds a missing argument 'struct mm_struct *' in pud_basic_tests() test
. This never got exposed before as PUD based THP is available only on X86
platform where mm_pmd_folded(mm) call gets macro replaced without requiring
the mm_struct i.e __is_defined(__PAGETABLE_PMD_FOLDED).

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Tested-by: Gerald Schaefer <gerald.schaefer@de.ibm.com> [s390]
Reviewed-by: Steven Price <steven.price@arm.com>
Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
 mm/debug_vm_pgtable.c | 47 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 35 insertions(+), 12 deletions(-)

diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index 1842d97522bb..a9bd6ce1ba02 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -58,11 +58,13 @@
 #define RANDOM_ORVALUE (GENMASK(BITS_PER_LONG - 1, 0) & ~ARCH_SKIP_MASK)
 #define RANDOM_NZVALUE	GENMASK(7, 0)
 
-static void __init pte_basic_tests(unsigned long pfn, pgprot_t prot)
+static void __init pte_basic_tests(unsigned long pfn, int idx)
 {
+	pgprot_t prot = protection_map[idx];
 	pte_t pte = pfn_pte(pfn, prot);
+	unsigned long val = idx, *ptr = &val;
 
-	pr_debug("Validating PTE basic\n");
+	pr_debug("Validating PTE basic (%pGv)\n", ptr);
 
 	/*
 	 * This test needs to be executed after the given page table entry
@@ -141,14 +143,16 @@ static void __init pte_savedwrite_tests(unsigned long pfn, pgprot_t prot)
 }
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-static void __init pmd_basic_tests(unsigned long pfn, pgprot_t prot)
+static void __init pmd_basic_tests(unsigned long pfn, int idx)
 {
+	pgprot_t prot = protection_map[idx];
 	pmd_t pmd = pfn_pmd(pfn, prot);
+	unsigned long val = idx, *ptr = &val;
 
 	if (!has_transparent_hugepage())
 		return;
 
-	pr_debug("Validating PMD basic\n");
+	pr_debug("Validating PMD basic (%pGv)\n", ptr);
 
 	/*
 	 * This test needs to be executed after the given page table entry
@@ -274,14 +278,16 @@ static void __init pmd_savedwrite_tests(unsigned long pfn, pgprot_t prot)
 }
 
 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
-static void __init pud_basic_tests(unsigned long pfn, pgprot_t prot)
+static void __init pud_basic_tests(struct mm_struct *mm, unsigned long pfn, int idx)
 {
+	pgprot_t prot = protection_map[idx];
 	pud_t pud = pfn_pud(pfn, prot);
+	unsigned long val = idx, *ptr = &val;
 
 	if (!has_transparent_hugepage())
 		return;
 
-	pr_debug("Validating PUD basic\n");
+	pr_debug("Validating PUD basic (%pGv)\n", ptr);
 
 	/*
 	 * This test needs to be executed after the given page table entry
@@ -398,7 +404,7 @@ static void __init pud_huge_tests(pud_t *pudp, unsigned long pfn, pgprot_t prot)
 #endif /* !CONFIG_HAVE_ARCH_HUGE_VMAP */
 
 #else  /* !CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
-static void __init pud_basic_tests(unsigned long pfn, pgprot_t prot) { }
+static void __init pud_basic_tests(struct mm_struct *mm, unsigned long pfn, int idx) { }
 static void __init pud_advanced_tests(struct mm_struct *mm,
 				      struct vm_area_struct *vma, pud_t *pudp,
 				      unsigned long pfn, unsigned long vaddr,
@@ -411,8 +417,8 @@ static void __init pud_huge_tests(pud_t *pudp, unsigned long pfn, pgprot_t prot)
 }
 #endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
 #else  /* !CONFIG_TRANSPARENT_HUGEPAGE */
-static void __init pmd_basic_tests(unsigned long pfn, pgprot_t prot) { }
-static void __init pud_basic_tests(unsigned long pfn, pgprot_t prot) { }
+static void __init pmd_basic_tests(unsigned long pfn, int idx) { }
+static void __init pud_basic_tests(struct mm_struct *mm, unsigned long pfn, int idx) { }
 static void __init pmd_advanced_tests(struct mm_struct *mm,
 				      struct vm_area_struct *vma, pmd_t *pmdp,
 				      unsigned long pfn, unsigned long vaddr,
@@ -938,6 +944,7 @@ static int __init debug_vm_pgtable(void)
 	unsigned long vaddr, pte_aligned, pmd_aligned;
 	unsigned long pud_aligned, p4d_aligned, pgd_aligned;
 	spinlock_t *ptl = NULL;
+	int idx;
 
 	pr_info("Validating architecture page table helpers\n");
 	prot = vm_get_page_prot(VMFLAGS);
@@ -1002,9 +1009,25 @@ static int __init debug_vm_pgtable(void)
 	saved_pmdp = pmd_offset(pudp, 0UL);
 	saved_ptep = pmd_pgtable(pmd);
 
-	pte_basic_tests(pte_aligned, prot);
-	pmd_basic_tests(pmd_aligned, prot);
-	pud_basic_tests(pud_aligned, prot);
+	/*
+	 * Iterate over the protection_map[] 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.
+	 */
+	for (idx = 0; idx < ARRAY_SIZE(protection_map); idx++) {
+		pte_basic_tests(pte_aligned, idx);
+		pmd_basic_tests(pmd_aligned, idx);
+		pud_basic_tests(mm, pud_aligned, idx);
+	}
+
+	/*
+	 * Both P4D and PGD level tests are very basic which do not
+	 * involve creating page table entries from the protection
+	 * value and the given pfn. Hence just keep them out from
+	 * the above iteration for now to save some test execution
+	 * time.
+	 */
 	p4d_basic_tests(p4d_aligned, prot);
 	pgd_basic_tests(pgd_aligned, prot);
 
-- 
2.20.1