On 10/4/25 01:36, Vivek Kasireddy wrote:
In addition to memfd, a blob resource can also have its backing
storage in a VFIO device region. Therefore, we first need to figure
out if the blob is backed by a VFIO device region or a memfd before
we can call the right API to get a dmabuf fd created.
So, once we have the ramblock and the associated mr, we rely on
memory_region_is_ram_device() to tell us where the backing storage
is located. If the blob resource is VFIO backed, we try to find the
right VFIO device that contains the blob and then invoke the API
vfio_device_create_dmabuf().
Note that in virtio_gpu_remap_udmabuf(), we first try to test if
the VFIO dmabuf exporter supports mmap or not. If it doesn't, we
use the VFIO device fd directly to create the CPU mapping.
Cc: Marc-André Lureau <[email protected]>
Cc: Alex Bennée <[email protected]>
Cc: Akihiko Odaki <[email protected]>
Cc: Dmitry Osipenko <[email protected]>
Signed-off-by: Vivek Kasireddy <[email protected]>
---
hw/display/Kconfig | 5 ++
hw/display/virtio-gpu-udmabuf.c | 143 ++++++++++++++++++++++++++++++--
2 files changed, 141 insertions(+), 7 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-udmabuf.c b/hw/display/virtio-gpu-udmabuf.c
index d804f321aa..bd06b4f300 100644
--- a/hw/display/virtio-gpu-udmabuf.c
+++ b/hw/display/virtio-gpu-udmabuf.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 +28,33 @@
#include "standard-headers/linux/udmabuf.h"
#include "standard-headers/drm/drm_fourcc.h"
+static void vfio_create_dmabuf(VFIODevice *vdev,
+ struct virtio_gpu_simple_resource *res)
+{
+#if defined(VIRTIO_GPU_VFIO_BLOB)
+ res->dmabuf_fd = vfio_device_create_dmabuf(vdev, res->iov, res->iov_cnt);
I didn't realize an fd was returned until this patch. I'd suggest
renaming vfio_device_create_dmabuf() to vfio_device_create_dmabuf_fd(),
or something explicit IMO.
+ if (res->dmabuf_fd < 0) {
+ qemu_log_mask(LOG_GUEST_ERROR,
+ "%s: VFIO_DEVICE_FEATURE_DMA_BUF: %s\n",
+ __func__, strerror(errno));
+ }
+#endif
+}
+
+static VFIODevice *vfio_device_lookup(MemoryRegion *mr)
+{
+#if defined(VIRTIO_GPU_VFIO_BLOB)
+ VFIODevice *vdev;
+
+ QLIST_FOREACH(vdev, &vfio_device_list, next) {
Hmm, I'm not sure we want to expose the VFIOdevice list to other
subsystems. I understand the need, and it's faster than iterating
over QOM devices, but I’d prefer that an API be provided for this
purpose.
I missed how much vfio_device_list has proliferated. Needs a check.
+ if (vdev->dev == mr->dev) {
+ return vdev;
+ }
+ }
+#endif
+ return NULL;
+}
+
static void virtio_gpu_create_udmabuf(struct virtio_gpu_simple_resource *res)
{
struct udmabuf_create_list *list;
@@ -68,11 +96,73 @@ static void virtio_gpu_create_udmabuf(struct
virtio_gpu_simple_resource *res)
g_free(list);
}
-static void virtio_gpu_remap_udmabuf(struct virtio_gpu_simple_resource *res)
+static void *vfio_dmabuf_mmap(struct virtio_gpu_simple_resource *res,
+ VFIODevice *vdev)
+{
+ struct vfio_region_info *info;
+ ram_addr_t offset, len = 0;
+ void *map, *submap;
+ int i, ret = -1;
+ RAMBlock *rb;
+
+ /*
+ * We first reserve a contiguous chunk of address space for the entire
+ * dmabuf, then replace it with smaller mappings that correspond to the
+ * individual segments of the dmabuf.
+ */
+ map = mmap(NULL, res->blob_size, PROT_READ, MAP_SHARED, vdev->fd, 0);
+ if (map == MAP_FAILED) {
+ return map;
+ }
+
+ for (i = 0; i < res->iov_cnt; i++) {
+ rcu_read_lock();
+ rb = qemu_ram_block_from_host(res->iov[i].iov_base, false, &offset);
+ rcu_read_unlock();
+
+ if (!rb) {
+ goto err;
+ }
+
+#if defined(VIRTIO_GPU_VFIO_BLOB)
+ ret = vfio_get_region_index_from_mr(rb->mr);
+ if (ret < 0) {
+ goto err;
+ }
+
+ ret = vfio_device_get_region_info(vdev, ret, &info);
+#endif
+ if (ret < 0) {
+ goto err;
+ }
"hmm" again. Not this patch fault but we lack proper documentation
for the VFIO API. Something to work on. Since this patch is using
vfio_device_get_region_info() could you please add documentation
for it ?
Thanks,
C.
+ submap = mmap(map + len, res->iov[i].iov_len, PROT_READ,
+ MAP_SHARED | MAP_FIXED, vdev->fd,
+ info->offset + offset);
+ if (submap == MAP_FAILED) {
+ goto err;
+ }
+
+ len += res->iov[i].iov_len;
+ }
+ return map;
+err:
+ munmap(map, res->blob_size);
+ return MAP_FAILED;
+}
+
+static void virtio_gpu_remap_udmabuf(struct virtio_gpu_simple_resource *res,
+ VFIODevice *vdev)
{
res->remapped = mmap(NULL, res->blob_size, PROT_READ,
MAP_SHARED, res->dmabuf_fd, 0);
if (res->remapped == MAP_FAILED) {
+ if (vdev) {
+ res->remapped = vfio_dmabuf_mmap(res, vdev);
+ if (res->remapped != MAP_FAILED) {
+ return;
+ }
+ }
warn_report("%s: dmabuf mmap failed: %s", __func__,
strerror(errno));
res->remapped = NULL;
@@ -130,18 +220,59 @@ bool virtio_gpu_have_udmabuf(void)
void virtio_gpu_init_udmabuf(struct virtio_gpu_simple_resource *res)
{
+ VFIODevice *vdev = NULL;
void *pdata = NULL;
+ ram_addr_t offset;
+ RAMBlock *rb;
res->dmabuf_fd = -1;
if (res->iov_cnt == 1 &&
res->iov[0].iov_len < 4096) {
pdata = res->iov[0].iov_base;
} else {
- virtio_gpu_create_udmabuf(res);
- if (res->dmabuf_fd < 0) {
+ rcu_read_lock();
+ rb = qemu_ram_block_from_host(res->iov[0].iov_base, false, &offset);
+ rcu_read_unlock();
+
+ if (!rb) {
+ qemu_log_mask(LOG_GUEST_ERROR,
+ "%s: Could not find ram block for host address\n",
+ __func__);
return;
}
- virtio_gpu_remap_udmabuf(res);
+
+ if (memory_region_is_ram_device(rb->mr)) {
+ vdev = vfio_device_lookup(rb->mr);
+ if (!vdev) {
+ qemu_log_mask(LOG_GUEST_ERROR,
+ "%s: Could not find device to create dmabuf\n",
+ __func__);
+ return;
+ }
+
+ vfio_create_dmabuf(vdev, res);
+ if (res->dmabuf_fd < 0) {
+ qemu_log_mask(LOG_GUEST_ERROR,
+ "%s: Could not create dmabuf from vfio device\n",
+ __func__);
+ return;
+ }
+ } else if (memory_region_is_ram(rb->mr) && virtio_gpu_have_udmabuf()) {
+ virtio_gpu_create_udmabuf(res);
+ if (res->dmabuf_fd < 0) {
+ qemu_log_mask(LOG_GUEST_ERROR,
+ "%s: Could not create dmabuf from memfd\n",
+ __func__);
+ return;
+ }
+ } else {
+ qemu_log_mask(LOG_GUEST_ERROR,
+ "%s: memory region cannot be used to create
dmabuf\n",
+ __func__);
+ return;
+ }
+
+ virtio_gpu_remap_udmabuf(res, vdev);
if (!res->remapped) {
return;
}
@@ -153,9 +284,7 @@ void virtio_gpu_init_udmabuf(struct
virtio_gpu_simple_resource *res)
void virtio_gpu_fini_udmabuf(struct virtio_gpu_simple_resource *res)
{
- if (res->remapped) {
- virtio_gpu_destroy_udmabuf(res);
- }
+ virtio_gpu_destroy_udmabuf(res);
}
static void virtio_gpu_free_dmabuf(VirtIOGPU *g, VGPUDMABuf *dmabuf)
