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)); 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); rc = pci_request_region(pci_dev, 0, "virtio-pci-legacy"); if (rc) -- 2.1.4 _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
