[v6,2/9] mm: x86: add CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG

Commit Message

Yu Zhao Jan. 4, 2022, 8:22 p.m. UTC

Some architectures support the accessed bit in non-leaf PMD entries,
e.g., x86_64 sets the accessed bit in a non-leaf PMD entry when using
it as part of linear address translation [1]. Page table walkers that
clear the accessed bit may use this feature to reduce their search
space.

Although an inline function is preferable, this capability is added as
a configuration option for the consistency with the existing macros.

[1]: Intel 64 and IA-32 Architectures Software Developer's Manual
     Volume 3 (June 2021), section 4.8

Signed-off-by: Yu Zhao <[e-mail]>
Tested-by: Konstantin Kharlamov <[e-mail]>
---
 arch/Kconfig                   | 9 +++++++++
 arch/x86/Kconfig               | 1 +
 arch/x86/include/asm/pgtable.h | 3 ++-
 arch/x86/mm/pgtable.c          | 5 ++++-
 include/linux/pgtable.h        | 4 ++--
 5 files changed, 18 insertions(+), 4 deletions(-)

Comments

Linus Torvalds Jan. 4, 2022, 9:24 p.m. UTC | #1

On Tue, Jan 4, 2022 at 12:23 PM Yu Zhao <[e-mail]> wrote:
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 5c2ccb85f2ef..5a4843242f09 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -85,6 +85,7 @@ config X86
> +       select ARCH_HAS_NONLEAF_PMD_YOUNG       if X86_64

Why is this limited to 64-bit?

I'm ok with that - maybe it's a simple case of "this is not worth
doing on 32-bit", but I'd like the explanation to be written out.

Right now the commit message literally points the architecture manual
that sio relevant for both 32-bit and 64-bit - and then the patch
itself makes it 64-bit only.

              Linus

Patch

diff --git a/arch/Kconfig b/arch/Kconfig
index d3c4ab249e9c..10f564340f79 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1312,6 +1312,15 @@  config ARCH_HAS_PARANOID_L1D_FLUSH
 config DYNAMIC_SIGFRAME
 	bool
 
+config ARCH_HAS_NONLEAF_PMD_YOUNG
+	bool
+	depends on PGTABLE_LEVELS > 2
+	help
+	  Architectures that select this option are capable of setting the
+	  accessed bit in non-leaf PMD entries when using them as part of linear
+	  address translations. Page table walkers that clear the accessed bit
+	  may use this feature to reduce their search space.
+
 source "kernel/gcov/Kconfig"
 
 source "scripts/gcc-plugins/Kconfig"
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5c2ccb85f2ef..5a4843242f09 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -85,6 +85,7 @@  config X86
 	select ARCH_HAS_PMEM_API		if X86_64
 	select ARCH_HAS_PTE_DEVMAP		if X86_64
 	select ARCH_HAS_PTE_SPECIAL
+	select ARCH_HAS_NONLEAF_PMD_YOUNG	if X86_64
 	select ARCH_HAS_UACCESS_FLUSHCACHE	if X86_64
 	select ARCH_HAS_COPY_MC			if X86_64
 	select ARCH_HAS_SET_MEMORY
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index c60b16f8b741..36205ec0acac 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -817,7 +817,8 @@  static inline unsigned long pmd_page_vaddr(pmd_t pmd)
 
 static inline int pmd_bad(pmd_t pmd)
 {
-	return (pmd_flags(pmd) & ~_PAGE_USER) != _KERNPG_TABLE;
+	return (pmd_flags(pmd) & ~(_PAGE_USER | _PAGE_ACCESSED)) !=
+	       (_KERNPG_TABLE & ~_PAGE_ACCESSED);
 }
 
 static inline unsigned long pages_to_mb(unsigned long npg)
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 3481b35cb4ec..a224193d84bf 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -550,7 +550,7 @@  int ptep_test_and_clear_young(struct vm_area_struct *vma,
 	return ret;
 }
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG)
 int pmdp_test_and_clear_young(struct vm_area_struct *vma,
 			      unsigned long addr, pmd_t *pmdp)
 {
@@ -562,6 +562,9 @@  int pmdp_test_and_clear_young(struct vm_area_struct *vma,
 
 	return ret;
 }
+#endif
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 int pudp_test_and_clear_young(struct vm_area_struct *vma,
 			      unsigned long addr, pud_t *pudp)
 {
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 53bd6a26918f..b51f939a73f7 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -211,7 +211,7 @@  static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
 #endif
 
 #ifndef __HAVE_ARCH_PMDP_TEST_AND_CLEAR_YOUNG
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG)
 static inline int pmdp_test_and_clear_young(struct vm_area_struct *vma,
 					    unsigned long address,
 					    pmd_t *pmdp)
@@ -232,7 +232,7 @@  static inline int pmdp_test_and_clear_young(struct vm_area_struct *vma,
 	BUILD_BUG();
 	return 0;
 }
-#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG */
 #endif
 
 #ifndef __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH