linux-kernel - Re: [Xen-devel] [PATCH v2 33/34] xenbus: use virt

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Message-ID: <568A5830.9000501@citrix.com>
Date:	Mon, 4 Jan 2016 11:32:00 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>,
	<linux-kernel@...r.kernel.org>
CC:	<linux-mips@...ux-mips.org>, <linux-ia64@...r.kernel.org>,
	<linux-sh@...r.kernel.org>, Peter Zijlstra <peterz@...radead.org>,
	<virtualization@...ts.linux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, <sparclinux@...r.kernel.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	<linux-arch@...r.kernel.org>, <linux-s390@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>, <x86@...nel.org>,
	<xen-devel@...ts.xenproject.org>, Ingo Molnar <mingo@...e.hu>,
	<linux-xtensa@...ux-xtensa.org>,
	<user-mode-linux-devel@...ts.sourceforge.net>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	<adi-buildroot-devel@...ts.sourceforge.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	<linux-metag@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	David Vrabel <david.vrabel@...rix.com>,
	<linuxppc-dev@...ts.ozlabs.org>, David Miller <davem@...emloft.net>
Subject: Re: [Xen-devel] [PATCH v2 33/34] xenbus: use virt_xxx barriers

On 31/12/15 19:10, Michael S. Tsirkin wrote:
> drivers/xen/xenbus/xenbus_comms.c 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.

Acked-by: David Vrabel <david.vrabel@...rix.com>

If you're feeling particularly keen there's a rmb() consume_one_event()
in drivers/xen/events/events_fifo.c that can be converted to virt_rmb()
as well.

David
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