Dmitry Osipenko <[email protected]> writes: > 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!
Thanks, a proposed followup for the Sashiko-bot reported issue submitted: https://lore.kernel.org/dri-devel/[email protected]/
