Subject: Re: [PATCH v6 11/11] virtio-gpu-dmabuf: Create dmabuf for
blobs associated with VFIO devices
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 <[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/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.
