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Date: Fri, 1 Jan 2016 20:23:46 +0300
From: Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To: "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Cc: Peter Zijlstra <peterz@...radead.org>,
Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
Andrew Cooper <andrew.cooper3@...rix.com>,
virtualization@...ts.linux-foundation.org,
Stefano Stabellini <stefano.stabellini@...citrix.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
David Miller <davem@...emloft.net>, linux-ia64@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
sparclinux@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-metag@...r.kernel.org, linux-mips@...ux-mips.org,
x86@...nel.org, user-mode-linux-devel@...ts.sourceforge.net,
adi-buildroot-devel@...ts.sourceforge.net,
linux-sh@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
xen-devel@...ts.xenproject.org
Subject: Re: [PATCH v2 32/32] virtio_ring: use virt_store_mb
Hello.
On 12/31/2015 10:09 PM, Michael S. Tsirkin wrote:
> We need a full barrier after writing out event index, using
> virt_store_mb there seems better than open-coding. As usual, we need a
> wrapper to account for strong barriers.
>
> It's tempting to use this in vhost as well, for that, we'll
> need a variant of smp_store_mb that works on __user pointers.
>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
> include/linux/virtio_ring.h | 12 ++++++++++++
> drivers/virtio/virtio_ring.c | 15 +++++++++------
> 2 files changed, 21 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
> index f3fa55b..3a74d91 100644
> --- a/include/linux/virtio_ring.h
> +++ b/include/linux/virtio_ring.h
> @@ -45,6 +45,18 @@ static inline void virtio_wmb(bool weak_barriers)
> wmb();
> }
>
> +static inline void virtio_store_mb(bool weak_barriers,
> + __virtio16 *p, __virtio16 v)
> +{
> + if (weak_barriers)
> + virt_store_mb(*p, v);
> + else
> + {
The kernel coding style dictates:
if (weak_barriers) {
virt_store_mb(*p, v);
} else {
> + WRITE_ONCE(*p, v);
> + mb();
> + }
> +}
> +
[...]
MBR, Sergei
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