4.9-stable review patch. If anyone has any objections, please let me know.
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From: Naoya Horiguchi n-horiguchi@ah.jp.nec.com
commit eee4818baac0f2b37848fdf90e4b16430dc536ac upstream
_PAGE_PSE is used to distinguish between a truly non-present (_PAGE_PRESENT=0) PMD, and a PMD which is undergoing a THP split and should be treated as present.
But _PAGE_SWP_SOFT_DIRTY currently uses the _PAGE_PSE bit, which would cause confusion between one of those PMDs undergoing a THP split, and a soft-dirty PMD. Dropping _PAGE_PSE check in pmd_present() does not work well, because it can hurt optimization of tlb handling in thp split.
Thus, we need to move the bit.
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.
[dwmw2: Pulled in to 4.9 backport to support L1TF changes]
Link: http://lkml.kernel.org/r/20170717193955.20207-3-zi.yan@sent.com Signed-off-by: Naoya Horiguchi n-horiguchi@ah.jp.nec.com Signed-off-by: Zi Yan zi.yan@cs.rutgers.edu Acked-by: Dave Hansen dave.hansen@intel.com Cc: "H. Peter Anvin" hpa@zytor.com Cc: Anshuman Khandual khandual@linux.vnet.ibm.com Cc: David Nellans dnellans@nvidia.com Cc: Ingo Molnar mingo@elte.hu Cc: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Mel Gorman mgorman@techsingularity.net Cc: Minchan Kim minchan@kernel.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Vlastimil Babka vbabka@suse.cz Cc: Andrea Arcangeli aarcange@redhat.com Cc: Michal Hocko mhocko@kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: David Woodhouse dwmw@amazon.co.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/include/asm/pgtable_64.h | 12 +++++++++--- arch/x86/include/asm/pgtable_types.h | 10 +++++----- 2 files changed, 14 insertions(+), 8 deletions(-)
--- a/arch/x86/include/asm/pgtable_64.h +++ b/arch/x86/include/asm/pgtable_64.h @@ -166,15 +166,21 @@ static inline int pgd_large(pgd_t pgd) { /* * Encode and de-code a swap entry * - * | ... | 11| 10| 9|8|7|6|5| 4| 3|2|1|0| <- bit number - * | ... |SW3|SW2|SW1|G|L|D|A|CD|WT|U|W|P| <- bit names - * | OFFSET (14->63) | TYPE (9-13) |0|X|X|X| X| X|X|X|0| <- swp entry + * | ... | 11| 10| 9|8|7|6|5| 4| 3|2| 1|0| <- bit number + * | ... |SW3|SW2|SW1|G|L|D|A|CD|WT|U| W|P| <- bit names + * | OFFSET (14->63) | TYPE (9-13) |0|0|X|X| X| X|X|SD|0| <- swp entry * * G (8) is aliased and used as a PROT_NONE indicator for * !present ptes. We need to start storing swap entries above * there. We also need to avoid using A and D because of an * erratum where they can be incorrectly set by hardware on * non-present PTEs. + * + * SD (1) in swp entry is used to store soft dirty bit, which helps us + * remember soft dirty over page migration + * + * Bit 7 in swp entry should be 0 because pmd_present checks not only P, + * but also L and G. */ #define SWP_TYPE_FIRST_BIT (_PAGE_BIT_PROTNONE + 1) #define SWP_TYPE_BITS 5 --- 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