From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Add a field (->saw_unset_a_or_d) to the asm-generic version of
mmu_gather. We will use this on x86 to indicate when a PTE got
cleared that might potentially have a stray Accessed or Dirty bit
set.
Note that since ->saw_unset_a_or_d shares space in a bitfield
with ->fullmm and ->need_flush_all, there's no incremental
storage cost. In addition, since it is initialized to 0 like
->need_flush_all, they can likely be initialized together,
leading to no real cost for having ->saw_unset_a_or_d around.
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
---
b/include/asm-generic/tlb.h | 7 ++++++-
b/mm/memory.c | 6 ++++--
2 files changed, 10 insertions(+), 3 deletions(-)
diff -puN include/asm-generic/tlb.h~knl-leak-20-saw_unset_a_or_d include/asm-generic/tlb.h
--- a/include/asm-generic/tlb.h~knl-leak-20-saw_unset_a_or_d 2016-06-30 17:10:41.606203608 -0700
+++ b/include/asm-generic/tlb.h 2016-06-30 17:10:41.611203835 -0700
@@ -101,7 +101,12 @@ struct mmu_gather {
unsigned int fullmm : 1,
/* we have performed an operation which
* requires a complete flush of the tlb */
- need_flush_all : 1;
+ need_flush_all : 1,
+ /* we cleared a PTE bit which may potentially
+ * get set by hardware */
+ saw_unset_a_or_d: 1;
+
+
struct mmu_gather_batch *active;
struct mmu_gather_batch local;
diff -puN mm/memory.c~knl-leak-20-saw_unset_a_or_d mm/memory.c
--- a/mm/memory.c~knl-leak-20-saw_unset_a_or_d 2016-06-30 17:10:41.607203654 -0700
+++ b/mm/memory.c 2016-06-30 17:10:41.614203971 -0700
@@ -222,8 +222,10 @@ void tlb_gather_mmu(struct mmu_gather *t
tlb->mm = mm;
/* Is it from 0 to ~0? */
- tlb->fullmm = !(start | (end+1));
- tlb->need_flush_all = 0;
+ tlb->fullmm = !(start | (end+1));
+ tlb->need_flush_all = 0;
+ tlb->saw_unset_a_or_d = 0;
+
tlb->local.next = NULL;
tlb->local.nr = 0;
tlb->local.max = ARRAY_SIZE(tlb->__pages);
_
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