x86/mm: Ignore A/D bits in pte/pmd/pud_none()

The erratum we are fixing here can lead to stray setting of the
A and D bits.  That means that a pte that we cleared might
suddenly have A/D set.  So, stop considering those bits when
determining if a pte is pte_none().  The same goes for the
other pmd_none() and pud_none().  pgd_none() can be skipped
because it is not affected; we do not use PGD entries for
anything other than pagetables on affected configurations.

This adds a tiny amount of overhead to all pte_none() checks.
I doubt we'll be able to measure it anywhere.

Signed-off-by: Dave Hansen <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Luis R. Rodriguez <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Toshi Kani <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 1a27396b6ea04df12b2cff8930341320e7a4a819..2815d268af8bb797f21b0acee2cd16fd8874eec4 100644 (file)
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -480,7 +480,7 @@ pte_t *populate_extra_pte(unsigned long vaddr);
 
 static inline int pte_none(pte_t pte)
 {
-       return !pte.pte;
+       return !(pte.pte & ~(_PAGE_KNL_ERRATUM_MASK));
 }
 
 #define __HAVE_ARCH_PTE_SAME
@@ -552,7 +552,8 @@ static inline int pmd_none(pmd_t pmd)
 {
        /* Only check low word on 32-bit platforms, since it might be
           out of sync with upper half. */
-       return (unsigned long)native_pmd_val(pmd) == 0;
+       unsigned long val = native_pmd_val(pmd);
+       return (val & ~_PAGE_KNL_ERRATUM_MASK) == 0;
 }
 
 static inline unsigned long pmd_page_vaddr(pmd_t pmd)
@@ -616,7 +617,7 @@ static inline unsigned long pages_to_mb(unsigned long npg)
 #if CONFIG_PGTABLE_LEVELS > 2
 static inline int pud_none(pud_t pud)
 {
-       return native_pud_val(pud) == 0;
+       return (native_pud_val(pud) & ~(_PAGE_KNL_ERRATUM_MASK)) == 0;
 }
 
 static inline int pud_present(pud_t pud)
@@ -694,6 +695,12 @@ static inline int pgd_bad(pgd_t pgd)
 
 static inline int pgd_none(pgd_t pgd)
 {
+       /*
+        * There is no need to do a workaround for the KNL stray
+        * A/D bit erratum here.  PGDs only point to page tables
+        * except on 32-bit non-PAE which is not supported on
+        * KNL.
+        */
        return !native_pgd_val(pgd);
 }
 #endif /* CONFIG_PGTABLE_LEVELS > 3 */

diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index 7b5efe264eff253d1bbb9ea69fbca9caadf44389..d14d0a55322ad67c19d5893fad27bf5ffd627fc2 100644 (file)
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -70,6 +70,12 @@
                         _PAGE_PKEY_BIT2 | \
                         _PAGE_PKEY_BIT3)
 
+#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
+#define _PAGE_KNL_ERRATUM_MASK (_PAGE_DIRTY | _PAGE_ACCESSED)
+#else
+#define _PAGE_KNL_ERRATUM_MASK 0
+#endif
+
 #ifdef CONFIG_KMEMCHECK
 #define _PAGE_HIDDEN   (_AT(pteval_t, 1) << _PAGE_BIT_HIDDEN)
 #else