On 2026/03/05 15:54, 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]>
Signed-off-by: Vivek Kasireddy <[email protected]>
---
hw/display/virtio-gpu-dmabuf.c | 24 +++++++++++++++++++-----
1 file changed, 19 insertions(+), 5 deletions(-)
diff --git a/hw/display/virtio-gpu-dmabuf.c b/hw/display/virtio-gpu-dmabuf.c
index dd64fbbc2d..7f4c399416 100644
--- a/hw/display/virtio-gpu-dmabuf.c
+++ b/hw/display/virtio-gpu-dmabuf.c
@@ -136,7 +136,7 @@ bool virtio_gpu_have_udmabuf(void)
void virtio_gpu_init_dmabuf(struct virtio_gpu_simple_resource *res)
{
- Error *local_err = NULL;
+ Error *local_err = NULL, *vfio_err = NULL;
void *pdata = NULL;
int ret;
@@ -155,10 +155,24 @@ void virtio_gpu_init_dmabuf(struct virtio_gpu_simple_resource *res)
}
if (ret == VFIO_DMABUF_CREATE_ERR_INVALID_IOV) {
- qemu_log_mask(LOG_GUEST_ERROR,
- "Cannot create dmabuf: incompatible memory\n");
- error_free(local_err);
- return;
+ ret = vfio_device_create_dmabuf_fd(res->iov, res->iov_cnt,
+ &vfio_err);
+ if (ret > 0) {
Zero represents a success by convention.
+ if (vfio_device_mmap_dmabuf(res->iov, res->iov_cnt, &pdata,
+ res->blob_size, &vfio_err)) {
+ error_free(local_err);
+ goto out;
+ }
+ }
+
+ if (ret == VFIO_DMABUF_CREATE_ERR_INVALID_IOV) {
+ qemu_log_mask(LOG_GUEST_ERROR,
+ "Cannot create dmabuf: incompatible memory\n");
+ error_free(vfio_err);
+ error_free(local_err);
+ return;
+ }
+ error_report_err(vfio_err);
}
error_report_err(local_err);
This reports invalid IOV even when it is actually a valid pointer to
VFIO and the VFIO is failing. Such an error report does not help and we
should instead report only the VFIO error.
And there is another bug with the previous patch where res->dmabuf_fd is
invalid when virtio_gpu_remap_dmabuf() uses it.
Below is my attempt to fix these issues:
if (res->iov_cnt == 1 &&
res->iov[0].iov_len < 4096) {
res->dmabuf_fd = -1;
pdata = res->iov[0].iov_base;
} else {
res->dmabuf_fd = virtio_gpu_create_udmabuf(res, &local_err);
if (res->dmabuf_fd == VFIO_DMABUF_CREATE_ERR_INVALID_IOV) {
error_free_or_abort(local_err);
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) {
res->dmabuf_fd = -1;
error_free_or_abort(local_err);
qemu_log_mask(LOG_GUEST_ERROR,
"Cannot create dmabuf: incompatible
memory\n");
return;
}
if (res->dmabuf_fd < 0 ||
!vfio_device_mmap_dmabuf(res->iov, res->iov_cnt, &pdata,
res->blob_size, &local_err)) {
res->dmabuf_fd = -1;
}
} else if (res->dmabuf_fd < 0 ||
!virtio_gpu_remap_dmabuf(res, &pdata, &local_err)) {
res->dmabuf_fd = -1;
}
if (res->dmabuf_fd < 0) {
error_report_err(local_err);
return;
}
res->remapped = pdata;
}
Regards,
Akihiko Odaki
return;
