linux-kernel - Re: [PATCH] iommu/amd: Use try_cmpxchg64 in alloc_pte and free_clear

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Message-ID: <YrQZ1PQIXfNYSq5g@8bytes.org>
Date:   Thu, 23 Jun 2022 09:44:20 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Uros Bizjak <ubizjak@...il.com>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH] iommu/amd: Use try_cmpxchg64 in alloc_pte and
 free_clear_pte

On Wed, May 25, 2022 at 04:54:16PM +0200, Uros Bizjak wrote:
> Use try_cmpxchg64 instead of cmpxchg64 (*ptr, old, new) != old in
> alloc_pte and free_clear_pte.  cmpxchg returns success in ZF flag, so this
> change saves a compare after cmpxchg (and related move instruction
> in front of cmpxchg). Also, remove racy explicit assignment to pteval
> when cmpxchg fails, this is what try_cmpxchg does implicitly from
> *pte in an atomic way.
> 
> Signed-off-by: Uros Bizjak <ubizjak@...il.com>
> Cc: Joerg Roedel <joro@...tes.org>
> Cc: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> Cc: Will Deacon <will@...nel.org>
> ---
>  drivers/iommu/amd/io_pgtable.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)

Applied, thanks.