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Re: [Qemu-devel] [PATCH] virtio: Make memory barriers be memory barriers

From: Avi Kivity
Subject: Re: [Qemu-devel] [PATCH] virtio: Make memory barriers be memory barriers
Date: Tue, 06 Sep 2011 12:28:40 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0) Gecko/20110816 Thunderbird/6.0

On 09/06/2011 09:55 AM, Paolo Bonzini wrote:
On 09/06/2011 05:12 AM, David Gibson wrote:
I'm not "fixing ppc".  I'm fixing a fundamental flaw in the protocol
implementation._So far_  I've only observed the effects on ppc, but
that doesn't mean they don't exist.

Actually Michael is right. The implementation is correct on x86, though wrong anywhere else (perhaps s390?). On those architectures you do not need rmb() and wmb().

Are we sure? Nothing prevents the guest from using weakly-ordered writes, is there? For example, using MOVNTDQ.

Although in that case the guest is probably required to issue an SFENCE.

error compiling committee.c: too many arguments to function

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