4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Dave Hansen dave.hansen@linux.intel.com
commit 00839ee3b299303c6a5e26a0a2485427a3afcbbf upstream
This erratum can result in Accessed/Dirty getting set by the hardware when we do not expect them to be (on !Present PTEs).
Instead of trying to fix them up after this happens, we just allow the bits to get set and try to ignore them. We do this by shifting the layout of the bits we use for swap offset/type in our 64-bit PTEs.
It looks like this:
bitnrs: | ... | 11| 10| 9|8|7|6|5| 4| 3|2|1|0| names: | ... |SW3|SW2|SW1|G|L|D|A|CD|WT|U|W|P| before: | OFFSET (9-63) |0|X|X| TYPE(1-5) |0| after: | OFFSET (14-63) | TYPE (9-13) |0|X|X|X| X| X|X|X|0|
Note that D was already a don't care (X) even before. We just move TYPE up and turn its old spot (which could be hit by the A bit) into all don't cares.
We take 5 bits away from the offset, but that still leaves us with 50 bits which lets us index into a 62-bit swapfile (4 EiB). I think that's probably fine for the moment. We could theoretically reclaim 5 of the bits (1, 2, 3, 4, 7) but it doesn't gain us anything.
Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Cc: Andrew Morton akpm@linux-foundation.org Cc: Andy Lutomirski luto@kernel.org Cc: Borislav Petkov bp@alien8.de Cc: Brian Gerst brgerst@gmail.com Cc: Dave Hansen dave@sr71.net Cc: Denys Vlasenko dvlasenk@redhat.com Cc: H. Peter Anvin hpa@zytor.com Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Luis R. Rodriguez mcgrof@suse.com Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Toshi Kani toshi.kani@hp.com Cc: dave.hansen@intel.com Cc: linux-mm@kvack.org Cc: mhocko@suse.com Link: http://lkml.kernel.org/r/20160708001911.9A3FD2B6@viggo.jf.intel.com Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Guenter Roeck linux@roeck-us.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/include/asm/pgtable_64.h | 26 ++++++++++++++++++++------ 1 file changed, 20 insertions(+), 6 deletions(-)
--- a/arch/x86/include/asm/pgtable_64.h +++ b/arch/x86/include/asm/pgtable_64.h @@ -163,18 +163,32 @@ static inline int pgd_large(pgd_t pgd) { #define pte_offset_map(dir, address) pte_offset_kernel((dir), (address)) #define pte_unmap(pte) ((void)(pte))/* NOP */
-/* Encode and de-code a swap entry */ +/* + * 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 (10-13) |0|X|X|X| X| X|X|X|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. + */ +#define SWP_TYPE_FIRST_BIT (_PAGE_BIT_PROTNONE + 1) #define SWP_TYPE_BITS 5 -#define SWP_OFFSET_SHIFT (_PAGE_BIT_PROTNONE + 1) +/* Place the offset above the type: */ +#define SWP_OFFSET_FIRST_BIT (SWP_TYPE_FIRST_BIT + SWP_TYPE_BITS + 1)
#define MAX_SWAPFILES_CHECK() BUILD_BUG_ON(MAX_SWAPFILES_SHIFT > SWP_TYPE_BITS)
-#define __swp_type(x) (((x).val >> (_PAGE_BIT_PRESENT + 1)) \ +#define __swp_type(x) (((x).val >> (SWP_TYPE_FIRST_BIT)) \ & ((1U << SWP_TYPE_BITS) - 1)) -#define __swp_offset(x) ((x).val >> SWP_OFFSET_SHIFT) +#define __swp_offset(x) ((x).val >> SWP_OFFSET_FIRST_BIT) #define __swp_entry(type, offset) ((swp_entry_t) { \ - ((type) << (_PAGE_BIT_PRESENT + 1)) \ - | ((offset) << SWP_OFFSET_SHIFT) }) + ((type) << (SWP_TYPE_FIRST_BIT)) \ + | ((offset) << SWP_OFFSET_FIRST_BIT) }) #define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val((pte)) }) #define __swp_entry_to_pte(x) ((pte_t) { .pte = (x).val })