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

[Paolo Bonzini]

On 09/06/2011 11:28 AM, Avi Kivity wrote:
> > 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.

Yes, that's the guest problem.  You cannot do an SFENCE on the guest's 
behalf anyway.

Paolo