On 07/20/2018 09:29 AM, Anshuman Khandual wrote: > Now that virtio core always needs all virtio devices to have DMA OPS, we > need to make sure that the structure it points is the right one. In the > absence of VIRTIO_F_IOMMU_PLATFORM flag QEMU expects GPA from guest kernel. > In such case, virtio device must use default virtio_direct_dma_ops DMA OPS > structure which transforms scatter gather buffer addresses as GPA. This > DMA OPS override must happen as early as possible during virtio device > initializatin sequence before virtio core starts using given device's DMA > OPS callbacks for I/O transactions. This change detects device's IOMMU flag > and does the override in case the flag is cleared. > > Signed-off-by: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx> > --- > drivers/virtio/virtio.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c > index 7907ad3..6b13987 100644 > --- a/drivers/virtio/virtio.c > +++ b/drivers/virtio/virtio.c > @@ -166,6 +166,8 @@ void virtio_add_status(struct virtio_device *dev, unsigned int status) > } > EXPORT_SYMBOL_GPL(virtio_add_status); > > +const struct dma_map_ops virtio_direct_dma_ops; > + > int virtio_finalize_features(struct virtio_device *dev) > { > int ret = dev->config->finalize_features(dev); > @@ -174,6 +176,9 @@ int virtio_finalize_features(struct virtio_device *dev) > if (ret) > return ret; The previous patch removed the code block for XEN guests which forced the use of DMA API all the time irrespective of VIRTIO_F_IOMMU_PLATFORM flag on the device. Here is what I have removed with patch 2/4 which breaks the existing semantics on XEN guests. -static bool vring_use_dma_api(struct virtio_device *vdev) -{ - if (!virtio_has_iommu_quirk(vdev)) - return true; - - /* Otherwise, we are left to guess. */ - /* - * In theory, it's possible to have a buggy QEMU-supposed - * emulated Q35 IOMMU and Xen enabled at the same time. On - * such a configuration, virtio has never worked and will - * not work without an even larger kludge. Instead, enable - * the DMA API if we're a Xen guest, which at least allows - * all of the sensible Xen configurations to work correctly. - */ - if (xen_domain()) - return true; - - return false; -} XEN guests would not like override with virtio_direct_dma_ops in any case irrespective of the flag VIRTIO_F_IOMMU_PLATFORM. So the existing semantics can be preserved with something like this. It just assumes that dev->dma_ops is non-NULL and a valid one set by the architecture. If required we can add those tests here before skipping the override. diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c index 7907ad3..6b13987 100644 --- a/drivers/virtio/virtio.c +++ b/drivers/virtio/virtio.c @@ -166,6 +166,8 @@ void virtio_add_status(struct virtio_device *dev, unsigned int status) } EXPORT_SYMBOL_GPL(virtio_add_status); +const struct dma_map_ops virtio_direct_dma_ops; + int virtio_finalize_features(struct virtio_device *dev) { int ret = dev->config->finalize_features(dev); @@ -174,6 +176,9 @@ int virtio_finalize_features(struct virtio_device *dev) if (ret) return ret; + + if (xen_domain()) + goto skip_override; + + if (virtio_has_iommu_quirk(dev)) + set_dma_ops(dev->dev.parent, &virtio_direct_dma_ops); + + skip_override: + if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) return 0 Will incorporate these changes in the next version. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization