Hi Michael, On Wed, Sep 14, 2016 at 03:42:25PM +0300, Michael S. Tsirkin wrote: > On Wed, Sep 14, 2016 at 12:16:28PM +0100, Will Deacon wrote: > > Legacy virtio defines the virtqueue base using a 32-bit PFN field, with > > a read-only register indicating a fixed page size of 4k. > > > > This can cause problems for DMA allocators that allocate top down from > > the DMA mask, which is set to 64 bits. In this case, the addresses are > > silently truncated to 44-bit, leading to IOMMU faults, failure to read > > from the queue or data corruption. > > > > This patch restricts the DMA mask for legacy PCI virtio devices to > > 44 bits, which matches the specification. > > > > Cc: Andy Lutomirski <luto@xxxxxxxxxx> > > Cc: Michael S. Tsirkin <mst@xxxxxxxxxx> > > Cc: Benjamin Serebrin <serebrin@xxxxxxxxxx> > > Signed-off-by: Will Deacon <will.deacon@xxxxxxx> > > --- > > drivers/virtio/virtio_pci_legacy.c | 9 +++++++-- > > 1 file changed, 7 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/virtio/virtio_pci_legacy.c b/drivers/virtio/virtio_pci_legacy.c > > index 8c4e61783441..efb3f5dff4b7 100644 > > --- a/drivers/virtio/virtio_pci_legacy.c > > +++ b/drivers/virtio/virtio_pci_legacy.c > > @@ -212,12 +212,17 @@ int virtio_pci_legacy_probe(struct virtio_pci_device *vp_dev) > > return -ENODEV; > > } > > > > - rc = dma_set_mask_and_coherent(&pci_dev->dev, DMA_BIT_MASK(64)); > > + /* > > + * The virtio ring base address is expressed as a 32-bit PFN, with a > > + * page size of 1 << VIRTIO_PCI_QUEUE_ADDR_SHIFT. > > + */ > > + rc = dma_set_mask_and_coherent(&pci_dev->dev, > > + DMA_BIT_MASK(32 + VIRTIO_PCI_QUEUE_ADDR_SHIFT)); > > So why not limit just the coherent mask, as I suggested in a comment on v1? Sorry, I completely missed that suggestion. I'll roll a v3 with that included, although I'll rejig things a bit to make the error handling a bit more bearable. > > if (rc) > > rc = dma_set_mask_and_coherent(&pci_dev->dev, > > DMA_BIT_MASK(32)); > > if (rc) > > - dev_warn(&pci_dev->dev, "Failed to enable 64-bit or 32-bit DMA. Trying to continue, but this might not work.\n"); > > + dev_warn(&pci_dev->dev, "Failed to enable %d-bit or 32-bit DMA. Trying to continue, but this might not work.\n", 32 + VIRTIO_PCI_QUEUE_ADDR_SHIFT); > > > I'd rather we split this. I'll actually just leave like it was in the first place if we're trying a 64-bit streaming mask. Stay tuned, Will -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
