[Qemu-devel] Re: [PATCH-RFC 0/3] qemu: memory barriers in virtio

[Anthony Liguori]

On 12/22/2009 05:26 AM, Michael S. Tsirkin wrote:
> On Tue, Dec 08, 2009 at 06:18:18PM +0200, Michael S. Tsirkin wrote:
>    
> > The following fixes a class of long-standing bugs in qemu:
> > when kvm is enabled, guest might access device structures
> > in memory while they are updated by qemu on another CPU.
> > In this scenario, memory barriers are necessary to prevent
> > host CPU from reordering memory accesses, which might confuse
> > the guest.
> >
> > This patch only fixes virtio, but other emulated devices
> > might have a similar bug. They'll need to be discovered
> > and addressed case by case.
> >
> > This is still under test ... meanwhile: any early feedback/flames?
> >
> >      
> Any comments on this one?
> The patch works fine in my testing, and even though
> it did not fix a crash that I hoped it will fix,
> it seems required for correctness... Right?
>    

It's definitely better than what we have.  Rusty mentioned something to 
me a bit ago about the barriers for virtio in the kernel needing some 
work.  I've been meaning to ask him about it in the context of this patch.

Rusty, am I remembering correctly or have I been sipping too much 
eggnog? :-)

Regards,

Anthony Liguori