From f487cf69cf1456ceb34857a50474373aae42dd8a Mon Sep 17 00:00:00 2001 From: Dave Hansen Date: Wed, 10 Aug 2016 10:23:25 -0700 Subject: [PATCH] x86/mm: Fix swap entry comment and macro commit ace7fab7a6cdd363a615ec537f2aa94dbc761ee2 upstream A recent patch changed the format of a swap PTE. The comment explaining the format of the swap PTE is wrong about the bits used for the swap type field. Amusingly, the ASCII art and the patch description are correct, but the comment itself is wrong. As I was looking at this, I also noticed that the SWP_OFFSET_FIRST_BIT has an off-by-one error. This does not really hurt anything. It just wasted a bit of space in the PTE, giving us 2^59 bytes of addressable space in our swapfiles instead of 2^60. But, it doesn't match with the comments, and it wastes a bit of space, so fix it. Signed-off-by: Dave Hansen Cc: Andrew Morton Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Dave Hansen Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Luis R. Rodriguez Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Toshi Kani Fixes: 00839ee3b299 ("x86/mm: Move swap offset/type up in PTE to work around erratum") Link: http://lkml.kernel.org/r/20160810172325.E56AD7DA@viggo.jf.intel.com Signed-off-by: Ingo Molnar Signed-off-by: Guenter Roeck Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/asm/pgtable_64.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h index 225405b690b8..ce97c8c6a310 100644 --- a/arch/x86/include/asm/pgtable_64.h +++ b/arch/x86/include/asm/pgtable_64.h @@ -168,7 +168,7 @@ static inline int pgd_large(pgd_t pgd) { return 0; } * * | ... | 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 + * | OFFSET (14->63) | TYPE (9-13) |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 @@ -179,7 +179,7 @@ static inline int pgd_large(pgd_t pgd) { return 0; } #define SWP_TYPE_FIRST_BIT (_PAGE_BIT_PROTNONE + 1) #define SWP_TYPE_BITS 5 /* Place the offset above the type: */ -#define SWP_OFFSET_FIRST_BIT (SWP_TYPE_FIRST_BIT + SWP_TYPE_BITS + 1) +#define SWP_OFFSET_FIRST_BIT (SWP_TYPE_FIRST_BIT + SWP_TYPE_BITS) #define MAX_SWAPFILES_CHECK() BUILD_BUG_ON(MAX_SWAPFILES_SHIFT > SWP_TYPE_BITS)