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.
---
b/arch/x86/include/asm/pgtable.h | 13 ++++++++++---
b/arch/x86/include/asm/pgtable_types.h | 6 ++++++
2 files changed, 16 insertions(+), 3 deletions(-)
diff -puN arch/x86/include/asm/pgtable.h~knl-strays-20-mod-pte-none
arch/x86/include/asm/pgtable.h
--- a/arch/x86/include/asm/pgtable.h~knl-strays-20-mod-pte-none 2016-07-01
10:42:06.895771764 -0700
+++ b/arch/x86/include/asm/pgtable.h 2016-07-01 10:42:06.900771991 -0700
@@ -480,7 +480,7 @@ pte_t *populate_extra_pte(unsigned long
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(
#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 -puN arch/x86/include/asm/pgtable_types.h~knl-strays-20-mod-pte-none
arch/x86/include/asm/pgtable_types.h
--- a/arch/x86/include/asm/pgtable_types.h~knl-strays-20-mod-pte-none
2016-07-01 10:42:06.896771809 -0700
+++ b/arch/x86/include/asm/pgtable_types.h 2016-07-01 10:42:06.900771991
-0700
@@ -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
_
