Re: [PATCH v2 34/34] xen/io: use virt_xxx barriers

From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: linux-mips@linux-mips.org, linux-ia64@vger.kernel.org,
	linux-sh@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
	virtualization@lists.linux-foundation.org,
	"H. Peter Anvin" <hpa@zytor.com>,
	sparclinux@vger.kernel.org,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	linux-arch@vger.kernel.org, linux-s390@vger.kernel.org,
	Arnd Bergmann <arnd@arndb.de>,
	x86@kernel.org, xen-devel@lists.xenproject.org,
	Ingo Molnar <mingo@elte.hu>,
	linux-xtensa@linux-xtensa.org,
	user-mode-linux-devel@lists.sourceforge.net,
	Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
	adi-buildroot-devel@lists.sourceforge.net,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-metag@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	linux-kernel@vger.kernel.org,
	David Vrabel <david.vrabel@citrix.com>,
	linuxp
Subject: Re: [PATCH v2 34/34] xen/io: use virt_xxx barriers
Date: Mon, 4 Jan 2016 12:05:57 +0000	[thread overview]
Message-ID: <alpine.DEB.2.02.1601041201440.19710__21626.8101045445$1451909201$gmane$org@kaball.uk.xensource.com> (raw)
In-Reply-To: <1451572003-2440-35-git-send-email-mst@redhat.com>

On Thu, 31 Dec 2015, Michael S. Tsirkin wrote:
> include/xen/interface/io/ring.h uses
> full memory barriers to communicate with the other side.
> 
> For guests compiled with CONFIG_SMP, smp_wmb and smp_mb
> would be sufficient, so mb() and wmb() here are only needed if
> a non-SMP guest runs on an SMP host.
> 
> Switch to virt_xxx barriers which serve this exact purpose.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>


>  include/xen/interface/io/ring.h | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/include/xen/interface/io/ring.h b/include/xen/interface/io/ring.h
> index 7dc685b..21f4fbd 100644
> --- a/include/xen/interface/io/ring.h
> +++ b/include/xen/interface/io/ring.h
> @@ -208,12 +208,12 @@ struct __name##_back_ring {						\
>  
>  
>  #define RING_PUSH_REQUESTS(_r) do {					\
> -    wmb(); /* back sees requests /before/ updated producer index */	\
> +    virt_wmb(); /* back sees requests /before/ updated producer index */	\
>      (_r)->sring->req_prod = (_r)->req_prod_pvt;				\
>  } while (0)
>  
>  #define RING_PUSH_RESPONSES(_r) do {					\
> -    wmb(); /* front sees responses /before/ updated producer index */	\
> +    virt_wmb(); /* front sees responses /before/ updated producer index */	\
>      (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt;				\
>  } while (0)
>  
> @@ -250,9 +250,9 @@ struct __name##_back_ring {						\
>  #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do {		\
>      RING_IDX __old = (_r)->sring->req_prod;				\
>      RING_IDX __new = (_r)->req_prod_pvt;				\
> -    wmb(); /* back sees requests /before/ updated producer index */	\
> +    virt_wmb(); /* back sees requests /before/ updated producer index */	\
>      (_r)->sring->req_prod = __new;					\
> -    mb(); /* back sees new requests /before/ we check req_event */	\
> +    virt_mb(); /* back sees new requests /before/ we check req_event */	\
>      (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) <		\
>  		 (RING_IDX)(__new - __old));				\
>  } while (0)
> @@ -260,9 +260,9 @@ struct __name##_back_ring {						\
>  #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do {		\
>      RING_IDX __old = (_r)->sring->rsp_prod;				\
>      RING_IDX __new = (_r)->rsp_prod_pvt;				\
> -    wmb(); /* front sees responses /before/ updated producer index */	\
> +    virt_wmb(); /* front sees responses /before/ updated producer index */	\
>      (_r)->sring->rsp_prod = __new;					\
> -    mb(); /* front sees new responses /before/ we check rsp_event */	\
> +    virt_mb(); /* front sees new responses /before/ we check rsp_event */	\
>      (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) <		\
>  		 (RING_IDX)(__new - __old));				\
>  } while (0)
> @@ -271,7 +271,7 @@ struct __name##_back_ring {						\
>      (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);			\
>      if (_work_to_do) break;						\
>      (_r)->sring->req_event = (_r)->req_cons + 1;			\
> -    mb();								\
> +    virt_mb();								\
>      (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);			\
>  } while (0)
>  
> @@ -279,7 +279,7 @@ struct __name##_back_ring {						\
>      (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);			\
>      if (_work_to_do) break;						\
>      (_r)->sring->rsp_event = (_r)->rsp_cons + 1;			\
> -    mb();								\
> +    virt_mb();								\
>      (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);			\
>  } while (0)
>  
> -- 
> MST
>