Messages in this thread Patch in this message | | | Date | Tue, 17 Dec 2019 21:12:08 +0100 | From | Peter Zijlstra <> | Subject | [PATCH] asm-generic/tlb: Avoid potential double flush |
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On Tue, Dec 17, 2019 at 01:34:16PM +0100, Peter Zijlstra wrote: > Perhaps if we replace !tlb->end with something like: > > !tlb->freed_tables && !tlb->cleared_p* > > (which GCC should be able to do with a single load and mask) > > I've not really thought too hard about it yet, I need to run some > errands, but I'll look at it more closely when I get back.
AFAICT this should work.
--- Subject: asm-generic/tlb: Avoid potential double flush
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.
Reported-by: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- include/asm-generic/tlb.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h index fe0ea6ff3636..c9a25c5a83e8 100644 --- a/include/asm-generic/tlb.h +++ b/include/asm-generic/tlb.h @@ -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);
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