On Wed, 2015-10-28 at 11:15 +0900, Joerg Roedel wrote: > On Tue, Oct 27, 2015 at 06:17:10PM -0700, Andy Lutomirski wrote: > > From: Andy Lutomirski <luto@xxxxxxxxxxxxxx> > > > > This fixes virtio-pci on platforms and busses that have IOMMUs. > > This > > will break the experimental QEMU Q35 IOMMU support until QEMU is > > fixed. In exchange, it fixes physical virtio hardware as well as > > virtio-pci running under Xen. > > > > We should clean up the virtqueue API to do its own allocation and > > teach virtqueue_get_avail and virtqueue_get_used to return DMA > > addresses directly. > > > > Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx> > > --- > > drivers/virtio/virtio_pci_common.h | 3 ++- > > drivers/virtio/virtio_pci_legacy.c | 19 +++++++++++++++---- > > drivers/virtio/virtio_pci_modern.c | 34 ++++++++++++++++++++++++-- > > -------- > > 3 files changed, 41 insertions(+), 15 deletions(-) > > Same here, you need to call the dma_sync* functions when passing data > from/to the virtio-device. > > I think a good test for that is to boot a virtio kvm-guest with > swiotlb=force and see if it still works. That's useful but doesn't cover the cases where dma_wmb() is needed, right? We should make sure we're handling descriptors properly as we would for real hardware, and ensuring that addresses etc. are written to the descriptor (and a write barrier occurs) *before* the bit is set which tells the 'hardware' that it owns that descriptor. AFAICT we're currently setting the flags *first* in virtqueue_add(), let alone the missing write barrier between the two. -- dwmw2
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