[RFC 01/20] mm/tlb: fix fullmm semantics

Nadav Amit
2021-01-31T00:16:47Z

From: Nadav Amit <namit@vmware.com>

fullmm in mmu_gather is supposed to indicate that the mm is torn-down
(e.g., on process exit) and can therefore allow certain optimizations.
However, tlb_finish_mmu() sets fullmm, when in fact it want to say that
the TLB should be fully flushed.

Change tlb_finish_mmu() to set need_flush_all and check this flag in
tlb_flush_mmu_tlbonly() when deciding whether a flush is needed.

Signed-off-by: Nadav Amit <namit@vmware.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Nick Piggin <npiggin@gmail.com>
Cc: x86@kernel.org
---
include/asm-generic/tlb.h | 2 +-
mm/mmu_gather.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index 2c68a545ffa7..eea113323468 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -420,7 +420,7 @@ static inline void tlb_flush_mmu_tlbonly(struct mmu_gather *tlb)
* these bits.
*/
if (!(tlb->freed_tables || tlb->cleared_ptes || tlb->cleared_pmds ||
- tlb->cleared_puds || tlb->cleared_p4ds))
+ tlb->cleared_puds || tlb->cleared_p4ds || tlb->need_flush_all))
return;

tlb_flush(tlb);
diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
index 0dc7149b0c61..5a659d4e59eb 100644
--- a/mm/mmu_gather.c
+++ b/mm/mmu_gather.c
@@ -323,7 +323,7 @@ void tlb_finish_mmu(struct mmu_gather *tlb)
* On x86 non-fullmm doesn't yield significant difference
* against fullmm.
*/
- tlb->fullmm = 1;
+ tlb->need_flush_all = 1;
__tlb_reset_range(tlb);
tlb->freed_tables = 1;
}
--
2.25.1