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From: Bertrand Marquis <Bertrand.Marquis@arm.com>
To: Julien Grall <julien@xen.org>
Cc: Xen-devel <xen-devel@lists.xenproject.org>,
	Julien Grall <jgrall@amazon.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>, nd <nd@arm.com>
Subject: Re: [PATCH] xen/arm: cmpxchg: Add missing memory barriers in __cmpxchg_mb_timeout()
Date: Fri, 31 Jul 2020 12:50:34 +0000	[thread overview]
Message-ID: <0A749DCC-C7A6-4E4F-BE90-E06C93CE8E91@arm.com> (raw)
In-Reply-To: <20200730170721.23393-1-julien@xen.org>



> On 30 Jul 2020, at 19:07, Julien Grall <julien@xen.org> wrote:
> 
> From: Julien Grall <jgrall@amazon.com>
> 
> The function __cmpxchg_mb_timeout() was intended to have the same
> semantics as __cmpxchg_mb(). Unfortunately, the memory barriers were
> not added when first implemented.
> 
> There is no known issue with the existing callers, but the barriers are
> added given this is the expected semantics in Xen.
> 
> The issue was introduced by XSA-295.
> 
> Backport: 4.8+
> Fixes: 86b0bc958373 ("xen/arm: cmpxchg: Provide a new helper that can timeout")
> Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>

> ---
> xen/include/asm-arm/arm32/cmpxchg.h | 8 +++++++-
> xen/include/asm-arm/arm64/cmpxchg.h | 8 +++++++-
> 2 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/include/asm-arm/arm32/cmpxchg.h b/xen/include/asm-arm/arm32/cmpxchg.h
> index 49ca2a0d7ab1..0770f272ee99 100644
> --- a/xen/include/asm-arm/arm32/cmpxchg.h
> +++ b/xen/include/asm-arm/arm32/cmpxchg.h
> @@ -147,7 +147,13 @@ static always_inline bool __cmpxchg_mb_timeout(volatile void *ptr,
> 					       int size,
> 					       unsigned int max_try)
> {
> -	return __int_cmpxchg(ptr, old, new, size, true, max_try);
> +	bool ret;
> +
> +	smp_mb();
> +	ret = __int_cmpxchg(ptr, old, new, size, true, max_try);
> +	smp_mb();
> +
> +	return ret;
> }
> 
> #define cmpxchg(ptr,o,n)						\
> diff --git a/xen/include/asm-arm/arm64/cmpxchg.h b/xen/include/asm-arm/arm64/cmpxchg.h
> index 5bc2e1f78674..fc5c60f0bd74 100644
> --- a/xen/include/asm-arm/arm64/cmpxchg.h
> +++ b/xen/include/asm-arm/arm64/cmpxchg.h
> @@ -160,7 +160,13 @@ static always_inline bool __cmpxchg_mb_timeout(volatile void *ptr,
> 					       int size,
> 					       unsigned int max_try)
> {
> -	return __int_cmpxchg(ptr, old, new, size, true, max_try);
> +	bool ret;
> +
> +	smp_mb();
> +	ret = __int_cmpxchg(ptr, old, new, size, true, max_try);
> +	smp_mb();
> +
> +	return ret;
> }
> 
> #define cmpxchg(ptr, o, n) \
> -- 
> 2.17.1
> 
> 



      parent reply	other threads:[~2020-07-31 12:51 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-30 17:07 [PATCH] xen/arm: cmpxchg: Add missing memory barriers in __cmpxchg_mb_timeout() Julien Grall
2020-07-30 19:44 ` Stefano Stabellini
2020-07-31 12:50 ` Bertrand Marquis [this message]

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