[Devel] [PATCH vz8] ms/asm-generic/tlb: avoid potential double flush

[Konstantin Khorenko]

Disregard, the patch uses unknown field tlb->freed_tables.

--
Best regards,

Konstantin Khorenko,
Virtuozzo Linux Kernel Team

On 06/16/2021 03:50 PM, Konstantin Khorenko wrote:
> From: Peter Zijlstra <peterz at 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.
>
> Link: http://lkml.kernel.org/r/20200116064531.483522-4-aneesh.kumar@linux.ibm.com
> Signed-off-by: Peter Zijlstra (Intel) <peterz at infradead.org>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
> Reported-by: "Aneesh Kumar K.V" <aneesh.kumar at linux.ibm.com>
> Cc: Michael Ellerman <mpe at ellerman.id.au>
> Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
>
> https://jira.sw.ru/browse/PSBM-101300
> (cherry picked from ms commit 0758cd8304942292e95a0f750c374533db378b32)
> Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
>
> (cherry picked from vz7 commit f64be64b0e3d ("asm-generic/tlb: avoid
> potential double flush"))
>
> In the scope of https://jira.sw.ru/browse/PSBM-127854
> Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.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 81db3c11bb11..cdb5b3640784 100644
> --- a/include/asm-generic/tlb.h
> +++ b/include/asm-generic/tlb.h
> @@ -152,7 +152,12 @@ static inline void __tlb_reset_range(struct mmu_gather *tlb)
>
>  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);
>