Re: [PATCH v4 3/9] asm-generic/tlb: Avoid potential double flush

Aneesh Kumar K.V
2020-01-16T06:50:10Z

On 1/16/20 12:15 PM, Aneesh Kumar K.V wrote:
> From: Peter Zijlstra <peterz@infradead.org>
>
> 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.
>

We should possibly get this to stable too along with the first two
patches. I am not quiet sure if this will qualify for a stable backport.
Hence avoided adding Cc:stable@kernel.org

> Reported-by: "Aneesh Kumar K.V" <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>
> ---
> 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 9e22ac369d1d..b36b3bef5661 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);
>