Re: [Qemu-devel] [PATCHv4 3/3] virtio: order index/descriptor reads

2012-04-24 Thread Paolo Bonzini
Il 24/04/2012 18:21, Michael S. Tsirkin ha scritto: > > +#define smp_rmb() smp_mb() > + > #elif defined(__x86_64__) > This #define seems spurious, but I may be reading the patch wrong. Paolo

[Qemu-devel] [PATCHv4 3/3] virtio: order index/descriptor reads

2012-04-24 Thread Michael S. Tsirkin
virtio has the equivalent of: if (vq->last_avail_index != vring_avail_idx(vq)) { read descriptor head at vq->last_avail_index; } In theory, processor can reorder descriptor head read to happen speculatively before the index read. this would trigger the following ra