asm-generic/tlb: avoid potential double flush
authorPeter Zijlstra <peterz@infradead.org>
Tue, 4 Feb 2020 01:36:53 +0000 (17:36 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Tue, 4 Feb 2020 03:05:26 +0000 (03:05 +0000)
Aneesh reported that:

tlb_flush_mmu()
  tlb_flush_mmu_tlbonly()
    tlb_flush() <-- #1
  tlb_flush_mmu_free()
    tlb_table_flush()
      tlb_table_invalidate()
tlb_flush_mmu_tlbonly()
  tlb_flush() <-- #2

does two TLBIs when tlb->fullmm, because __tlb_reset_range() will not
clear tlb->end in that case.

Observe that any caller to __tlb_adjust_range() also sets at least one of
the tlb->freed_tables || tlb->cleared_p* bits, and those are
unconditionally cleared by __tlb_reset_range().

Change the condition for actually issuing TLBI to having one of those bits
set, as opposed to having tlb->end != 0.

Link: http://lkml.kernel.org/r/20200116064531.483522-4-aneesh.kumar@linux.ibm.com
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Reported-by: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
include/asm-generic/tlb.h

index 9e22ac3..b36b3be 100644 (file)
@@ -402,7 +402,12 @@ tlb_update_vma_flags(struct mmu_gather *tlb, struct vm_area_struct *vma) { }
 
 static inline void tlb_flush_mmu_tlbonly(struct mmu_gather *tlb)
 {
-       if (!tlb->end)
+       /*
+        * Anything calling __tlb_adjust_range() also sets at least one of
+        * these bits.
+        */
+       if (!(tlb->freed_tables || tlb->cleared_ptes || tlb->cleared_pmds ||
+             tlb->cleared_puds || tlb->cleared_p4ds))
                return;
 
        tlb_flush(tlb);