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

[Michael S. Tsirkin]

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?
 
> Michael S. Tsirkin (3):
>   qemu: add barriers.h header
>   virtio: use a real wmb
>   virtio: add missing barriers
> 
>  hw/barriers.h |  131 
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  hw/virtio.c   |   18 ++++----
>  2 files changed, 139 insertions(+), 10 deletions(-)
>  create mode 100644 hw/barriers.h
>