From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
pmd_present() checks _PAGE_PSE along with _PAGE_PRESENT to avoid
false negative return when it races with thp spilt
(during which _PAGE_PRESENT is temporary cleared.) I don't think that
dropping _PAGE_PSE check in pmd_present() works well because it can
hurt optimization of tlb handling in thp split.
In the current kernel, bits 1-4 are not used in non-present format
since commit 00839ee3b299 ("x86/mm: Move swap offset/type up in PTE to
work around erratum"). So let's move _PAGE_SWP_SOFT_DIRTY to bit 1.
Bit 7 is used as reserved (always clear), so please don't use it for
other purpose.
Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
ChangeLog v3:
- Move _PAGE_SWP_SOFT_DIRTY to bit 1, it was placed at bit 6. Because
some CPUs might accidentally set bit 5 or 6.
Signed-off-by: Zi Yan <zi.yan@xxxxxxxxxxxxxx>
---
arch/x86/include/asm/pgtable_types.h | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index 8b4de22d6429..3695abd58ef6 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -97,15 +97,15 @@
/*
* Tracking soft dirty bit when a page goes to a swap is tricky.
* We need a bit which can be stored in pte _and_ not conflict
- * with swap entry format. On x86 bits 6 and 7 are *not* involved
- * into swap entry computation, but bit 6 is used for nonlinear
- * file mapping, so we borrow bit 7 for soft dirty tracking.
+ * with swap entry format. On x86 bits 1-4 are *not* involved
+ * into swap entry computation, but bit 7 is used for thp migration,
+ * so we borrow bit 1 for soft dirty tracking.
*
* Please note that this bit must be treated as swap dirty page
- * mark if and only if the PTE has present bit clear!
+ * mark if and only if the PTE/PMD has present bit clear!
*/
#ifdef CONFIG_MEM_SOFT_DIRTY
-#define _PAGE_SWP_SOFT_DIRTY _PAGE_PSE
+#define _PAGE_SWP_SOFT_DIRTY _PAGE_RW
#else
#define _PAGE_SWP_SOFT_DIRTY (_AT(pteval_t, 0))
#endif
--
2.11.0
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