On 2026/10/08 5:09, 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_fd() API which identifies the right
VFIO device and eventually creates a dmabuf fd.
Note that, for mmapping the dmabuf, we directly call mmap() if the
dmabuf fd was created via virtio_gpu_create_udmabuf() since we know
that the udmabuf driver supports mmap(). However, if the dmabuf was
created via vfio_device_create_dmabuf_fd(), we use the
vfio_device_mmap_dmabuf() API to get a mapping for the dmabuf.
Cc: Marc-André Lureau <[email protected]>
Cc: Alex Bennée <[email protected]>
Cc: Akihiko Odaki <[email protected]>
Cc: Dmitry Osipenko <[email protected]>
Cc: Alex Williamson <[email protected]>
Cc: Cédric Le Goater <[email protected]>
Reviewed-by: Akihiko Odaki <[email protected]>
Signed-off-by: Vivek Kasireddy <[email protected]>
---
hw/display/virtio-gpu-dmabuf.c | 22 +++++++++++++++++++---
1 file changed, 19 insertions(+), 3 deletions(-)
diff --git a/hw/display/virtio-gpu-dmabuf.c b/hw/display/virtio-gpu-dmabuf.c
index c9de8e9ba3..f59a5e76ff 100644
--- a/hw/display/virtio-gpu-dmabuf.c
+++ b/hw/display/virtio-gpu-dmabuf.c
@@ -153,9 +153,25 @@ bool virtio_gpu_init_dmabuf(struct
virtio_gpu_simple_resource *res)
if (res->dmabuf_fd == VFIO_DMABUF_CREATE_ERR_INVALID_IOV) {
error_free_or_abort(&local_err);
- qemu_log_mask(LOG_GUEST_ERROR,
- "Cannot create dmabuf: incompatible memory\n");
- return false;
+ res->dmabuf_fd = vfio_device_create_dmabuf_fd(res->iov,
+ res->iov_cnt,
+ &local_err);
+ if (res->dmabuf_fd == VFIO_DMABUF_CREATE_ERR_INVALID_IOV) {
+ error_free_or_abort(&local_err);
+ qemu_log_mask(LOG_GUEST_ERROR,
+ "Cannot create dmabuf: incompatible memory\n");
+ return false;
+ }
+
+ if (res->dmabuf_fd >= 0) {
+ pdata = vfio_device_mmap_dmabuf(res->iov, res->iov_cnt,
+ &local_err);
This maps the complete IOV size, while virtio_gpu_fini_dmabuf() unmaps
only blob_size. Create and attach accept backing larger than the blob,
so excess pages remain mapped after detach, unref or reset.
Regards,
Akihiko Odaki
+ if (!pdata) {
+ virtio_gpu_fini_dmabuf(res);
+ }
+ } else {
+ res->dmabuf_fd = -1;
+ }
} else if (res->dmabuf_fd >= 0) {
pdata = virtio_gpu_remap_dmabuf(res, &local_err);
if (!pdata) {
