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(-) > > diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h > b/drivers/gpu/drm/virtio/virtgpu_drv.h > index 17a6a4d26516..09da7973387e 100644 > --- a/drivers/gpu/drm/virtio/virtgpu_drv.h > +++ b/drivers/gpu/drm/virtio/virtgpu_drv.h > @@ -43,6 +43,8 @@ > #include <drm/drm_probe_helper.h> > #include <drm/virtgpu_drm.h> > > +#include <xen/xen.h> > + > #define DRIVER_NAME "virtio_gpu" > #define DRIVER_DESC "virtio GPU" > > @@ -60,6 +62,24 @@ > /* See virtio_gpu_ctx_create. One additional character for NULL terminator. > */ > #define DEBUG_NAME_MAX_LEN 65 > > +/* > + * Whether the host must be told about resource backing pages by DMA address > + * rather than guest-physical address. > + * > + * This mirrors vring_use_map_api() in drivers/virtio/virtio_ring.c, > including > + * its xen_domain() case. > + */ > +static inline bool virtio_gpu_use_dma_api(const struct virtio_device *vdev) > +{ > + if (!virtio_has_dma_quirk(vdev)) > + return true; > + > + if (xen_domain()) > + return true; > + > + return false; > +} > + > struct virtio_gpu_object_params { > unsigned long size; > bool dumb; > diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c > b/drivers/gpu/drm/virtio/virtgpu_object.c > index 9bc0bd68c314..49899485be6f 100644 > --- a/drivers/gpu/drm/virtio/virtgpu_object.c > +++ b/drivers/gpu/drm/virtio/virtgpu_object.c > @@ -173,7 +173,7 @@ static int virtio_gpu_object_shmem_init(struct > virtio_gpu_device *vgdev, > struct virtio_gpu_mem_entry **ents, > unsigned int *nents) > { > - bool use_dma_api = !virtio_has_dma_quirk(vgdev->vdev); > + bool use_dma_api = virtio_gpu_use_dma_api(vgdev->vdev); > struct scatterlist *sg; > struct sg_table *pages; > int si; > diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c > b/drivers/gpu/drm/virtio/virtgpu_vq.c > index 905b1f42cd98..568fefd713e0 100644 > --- a/drivers/gpu/drm/virtio/virtgpu_vq.c > +++ b/drivers/gpu/drm/virtio/virtgpu_vq.c > @@ -764,7 +764,7 @@ int virtio_gpu_panic_cmd_transfer_to_host_2d(struct > virtio_gpu_device *vgdev, > struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(objs->objs[0]); > struct virtio_gpu_transfer_to_host_2d *cmd_p; > struct virtio_gpu_vbuffer *vbuf; > - bool use_dma_api = !virtio_has_dma_quirk(vgdev->vdev); > + bool use_dma_api = virtio_gpu_use_dma_api(vgdev->vdev); > > if (virtio_gpu_is_shmem(bo) && use_dma_api) > dma_sync_sgtable_for_device(vgdev->vdev->dev.parent, > @@ -795,7 +795,7 @@ void virtio_gpu_cmd_transfer_to_host_2d(struct > virtio_gpu_device *vgdev, > struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(objs->objs[0]); > struct virtio_gpu_transfer_to_host_2d *cmd_p; > struct virtio_gpu_vbuffer *vbuf; > - bool use_dma_api = !virtio_has_dma_quirk(vgdev->vdev); > + bool use_dma_api = virtio_gpu_use_dma_api(vgdev->vdev); > > if (virtio_gpu_is_shmem(bo) && use_dma_api) > dma_sync_sgtable_for_device(vgdev->vdev->dev.parent, > @@ -1231,7 +1231,7 @@ void virtio_gpu_cmd_transfer_to_host_3d(struct > virtio_gpu_device *vgdev, > struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(objs->objs[0]); > struct virtio_gpu_transfer_host_3d *cmd_p; > struct virtio_gpu_vbuffer *vbuf; > - bool use_dma_api = !virtio_has_dma_quirk(vgdev->vdev); > + bool use_dma_api = virtio_gpu_use_dma_api(vgdev->vdev); > > if (virtio_gpu_is_shmem(bo) && use_dma_api) > dma_sync_sgtable_for_device(vgdev->vdev->dev.parent, > > --- > base-commit: bd4f284df04d76fd65e57141cb1e6e7a49e4c3cb > change-id: 20260806-virtgpu-xen-dma-559fab712250 > > Best regards,
Looks okay, though I'm not familiar with Xen. Will apply to -next in a day if nobody will have objections. Acked-by: Dmitry Osipenko <[email protected]> -- Best regards, Dmitry
