On 2026/02/10 15:59, Vivek Kasireddy wrote:
> In addition to memfd, a blob resource can also have its backing
> storage in a VFIO device region. Since, there is no effective way
> to determine where the backing storage is located, we first try to
> create a dmabuf assuming it is in memfd. If that fails, we try to
> create a dmabuf assuming it is in VFIO device region.
>
> So, we first call virtio_gpu_create_udmabuf() to check if the blob's
> backing storage is located in a memfd or not. If it is not, we invoke
> the vfio_device_create_dmabuf() API which identifies the right VFIO
> device and eventually creates a dmabuf fd.
>
> Note that in virtio_gpu_remap_dmabuf(), we first try to test if
> the VFIO dmabuf exporter supports mmap or not. If it doesn't, we
> fall back to the vfio_device_mmap_dmabuf() API to get a mapping
> created for the dmabuf.
>
> Cc: Marc-André Lureau <marcandre.lureau@redhat.com>
> Cc: Alex Bennée <alex.bennee@linaro.org>
> Cc: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
> Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> Cc: Alex Williamson <alex@shazbot.org>
> Cc: Cédric Le Goater <clg@redhat.com>
> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
> ---
> hw/display/Kconfig | 5 ++++
> hw/display/virtio-gpu-dmabuf.c | 50 ++++++++++++++++++++++++++++------
> 2 files changed, 47 insertions(+), 8 deletions(-)
>
> diff --git a/hw/display/Kconfig b/hw/display/Kconfig
> index 1e95ab28ef..0d090f25f5 100644
> --- a/hw/display/Kconfig
> +++ b/hw/display/Kconfig
> @@ -106,6 +106,11 @@ config VIRTIO_VGA
> depends on VIRTIO_PCI
> select VGA
>
> +config VIRTIO_GPU_VFIO_BLOB
> + bool
> + default y
> + depends on VFIO
> +
> config VHOST_USER_GPU
> bool
> default y
> diff --git a/hw/display/virtio-gpu-dmabuf.c b/hw/display/virtio-gpu-dmabuf.c
> index d9b2ecaf31..54d010b995 100644
> --- a/hw/display/virtio-gpu-dmabuf.c
> +++ b/hw/display/virtio-gpu-dmabuf.c
> @@ -18,6 +18,7 @@
> #include "ui/console.h"
> #include "hw/virtio/virtio-gpu.h"
> #include "hw/virtio/virtio-gpu-pixman.h"
> +#include "hw/vfio/vfio-device.h"
> #include "trace.h"
> #include "system/ramblock.h"
> #include "system/hostmem.h"
> @@ -27,6 +28,27 @@
> #include "standard-headers/linux/udmabuf.h"
> #include "standard-headers/drm/drm_fourcc.h"
>
> +static bool virtio_gpu_create_vfio_dmabuf(struct virtio_gpu_simple_resource *r,
> + Error **errp)
> +{
> + bool ret = false;
> +#if defined(CONFIG_VIRTIO_GPU_VFIO_BLOB)
> + Error *local_err = NULL;
> + int fd;
> +
> + if (!vfio_device_create_dmabuf(r->iov, r->iov_cnt, &fd, &local_err)) {
> + error_report_err(*errp);
> + *errp = NULL;
> + error_propagate(errp, local_err);
> + return false;
> + }
> +
> + ret = true;
> + r->dmabuf_fd = fd;
> +#endif
> + return ret;
> +}
> +
> static bool virtio_gpu_create_udmabuf(struct virtio_gpu_simple_resource *res,
> Error **errp)
> {
> @@ -73,16 +95,28 @@ static bool virtio_gpu_create_udmabuf(struct virtio_gpu_simple_resource *res,
> static bool virtio_gpu_remap_dmabuf(struct virtio_gpu_simple_resource *res,
> Error **errp)
> {
> + Error *local_err = NULL;
> + bool ret = true;
> void *map;
>
> map = mmap(NULL, res->blob_size, PROT_READ, MAP_SHARED, res->dmabuf_fd, 0);
> if (map == MAP_FAILED) {
> error_setg_errno(errp, errno, "dmabuf mmap failed");
> - res->remapped = NULL;
> - return false;
> + map = NULL;
> + ret = false;
> +#if defined(CONFIG_VIRTIO_GPU_VFIO_BLOB)
> + if (vfio_device_mmap_dmabuf(res->iov, res->iov_cnt, &map,
> + res->blob_size, &local_err)) {
> + ret = true;
> + } else {
> + error_report_err(*errp);
> + *errp = NULL;
> + }
> +#endif
> + error_propagate(errp, local_err);
> }
> res->remapped = map;
> - return true;
> + return ret;
> }
>
> static void virtio_gpu_destroy_dmabuf(struct virtio_gpu_simple_resource *res)
> @@ -145,8 +179,10 @@ void virtio_gpu_init_dmabuf(struct virtio_gpu_simple_resource *res)
> pdata = res->iov[0].iov_base;
> } else {
> if (!virtio_gpu_create_udmabuf(res, &local_err)) {
virtio_gpu_create_udmabuf() will log "Could not find valid ramblock"
even for VFIO, which shouldn't happen.
This logic should look like as follows:
virtio_gpu_create_udmabuf(res);
if (it turned out the memory is incompatible with udmabuf) {
virtio_gpu_create_vfio_dmabuf(res);
if (it turned out the memory is not backed by VFIO) {
qemu_log_mask(LOG_GUEST_ERROR, "incompatible\n");
return;
}
}
Regards,
Akihiko Odaki
> - if (local_err) {
> - error_report_err(local_err);
> + if (!virtio_gpu_create_vfio_dmabuf(res, &local_err)) {
> + if (local_err) {
> + error_report_err(local_err);
> + }
> }
> return;
> }
> @@ -163,9 +199,7 @@ void virtio_gpu_init_dmabuf(struct virtio_gpu_simple_resource *res)
>
> void virtio_gpu_fini_dmabuf(struct virtio_gpu_simple_resource *res)
> {
> - if (res->remapped) {
> - virtio_gpu_destroy_dmabuf(res);
> - }
> + virtio_gpu_destroy_dmabuf(res);
> }
>
> static void virtio_gpu_free_dmabuf(VirtIOGPU *g, VGPUDMABuf *dmabuf)