[PATCH v12 02/14] mm: x86: add CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG

[Yu Zhao]

Some architectures support the accessed bit in non-leaf PMD entries,
e.g., x86 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 capability to reduce their search
space.

Note that:
1. Although an inline function is preferable, this capability is added
   as a configuration option for consistency with the existing macros.
2. Due to the little interest in other varieties, this capability was
   only tested on Intel and AMD CPUs.

Thanks to the following developers for their efforts [2][3].
  Randy Dunlap <rdunlap at infradead.org>
  Stephen Rothwell <sfr at canb.auug.org.au>

[1]: Intel 64 and IA-32 Architectures Software Developer's Manual
     Volume 3 (June 2021), section 4.8
[2] https://lore.kernel.org/r/bfdcc7c8-922f-61a9-aa15-7e7250f04af7@infradead.org/
[3] https://lore.kernel.org/r/20220413151513.5a0d7a7e@canb.auug.org.au/

Signed-off-by: Yu Zhao <yuzhao at google.com>
Reviewed-by: Barry Song <baohua at kernel.org>
Acked-by: Brian Geffon <bgeffon at google.com>
Acked-by: Jan Alexander Steffens (heftig) <heftig at archlinux.org>
Acked-by: Oleksandr Natalenko <oleksandr at natalenko.name>
Acked-by: Steven Barrett <steven at liquorix.net>
Acked-by: Suleiman Souhlal <suleiman at google.com>
Tested-by: Daniel Byrne <djbyrne at mtu.edu>
Tested-by: Donald Carr <d at chaos-reins.com>
Tested-by: Holger Hoffstätte <holger at applied-asynchrony.com>
Tested-by: Konstantin Kharlamov <Hi-Angel at yandex.ru>
Tested-by: Shuang Zhai <szhai2 at cs.rochester.edu>
Tested-by: Sofia Trinh <sofia.trinh at edi.works>
Tested-by: Vaibhav Jain <vaibhav at linux.ibm.com>
---
 arch/Kconfig                   | 8 ++++++++
 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, 17 insertions(+), 4 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index fcf9a41a4ef5..eaeec187bd6a 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1403,6 +1403,14 @@ config DYNAMIC_SIGFRAME
 config HAVE_ARCH_NODE_DEV_GROUP
 	bool
 
+config ARCH_HAS_NONLEAF_PMD_YOUNG
+	bool
+	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 capability 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 be0b95e51df6..5715111abe13 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 PGTABLE_LEVELS > 2
 	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 dc5f7d8ef68a..5059799bebe3 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -815,7 +815,8 @@ 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 a932d7712d85..8525f2876fb4 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 8eee31bc9bde..9c57c5cc49c2 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -213,7 +213,7 @@ 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)
@@ -234,7 +234,7 @@ 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
-- 
2.36.1.476.g0c4daa206d-goog