On 8/7/26 01:54, Benjamin Leggett via B4 Relay wrote: > From: Benjamin Leggett <[email protected]> > > On a Xen PV domain page addresses bear no relation to the real machine > addresses the host would have to use to reach it. > virtio_ring.c handles this correctly, vring_use_map_api() returns true > for any xen_domain() regardless of VIRTIO_F_ACCESS_PLATFORM. > > virtio-gpu makes the same decision independently, but its copy > looks only at the feature bit: > > bool use_dma_api = !virtio_has_dma_quirk(vgdev->vdev); > > QEMU does not set iommu_platform on virtio-vga by default, so > VIRTIO_F_ACCESS_PLATFORM is not negotiated, use_dma_api is false, and > virtio_gpu_object_shmem_init() describes the framebuffer's backing pages > to the host with sg_phys(). Those are guest-physical addresses. In a PV > domain they resolve, on the host side, to pages belonging to some other > domain, so the host scans out unrelated memory. > > Move the decision into virtio_gpu_use_dma_api() and give it the > xen_domain() check, like vring_use_map_api() has. This > additionally enables the dma_sync_sgtable_for_device() calls in > virtgpu_vq.c, which are required for correctness whenever swiotlb > is in play. > > Reproduced with a Xen 4.21 PV dom0 nested inside QEMU 8.2 with > virtio-vga, on both a distro 6.8 kernel and 6.18 LTS. A PVH dom0 > works fine and doesn't need this fix because it is identity-mapped, > only PV dom0s are affected. > > Fixes: a3b815f09bb8 ("drm/virtio: add iommu support.") > Signed-off-by: Ben Leggett <[email protected]> > --- > drivers/gpu/drm/virtio/virtgpu_drv.h | 20 ++++++++++++++++++++ > drivers/gpu/drm/virtio/virtgpu_object.c | 2 +- > drivers/gpu/drm/virtio/virtgpu_vq.c | 6 +++--- > 3 files changed, 24 insertions(+), 4 deletions(-)
Feel free to send follow-up patches to fix problems reported by the Sashiko bot. Applied to drm-misc-fixes, thanks! -- Best regards, Dmitry
