On 2025/11/16 23:14, Dmitry Osipenko wrote:
Support mapping virgl blobs to a fixed location of a hostmem memory
region using new virglrenderer MAP_FIXED API.
This new feature closes multiple problems for virtio-gpu on QEMU:
- Having dedicated memory region for each mapped blob works notoriously
slow due to QEMU's memory region software design built around RCU that
isn't optimized for frequent removal of the regions
- KVM isn't optimized for a frequent slot changes too
- QEMU/KVM has a limit for a total number of created memory regions,
crashing QEMU when limit is reached
This patch makes virtio-gpu-gl to pre-create a single anonymous memory
region covering whole hostmem area to which blobs will be mapped using
the MAP_FIXED API.
Not all virgl resources will support mapping at a fixed memory address. For
them, we will continue to create individual nested memory sub-regions. In
particular, vrend resources may not have MAP_FIXED capability.
Venus and DRM native contexts will largely benefit from the MAP_FIXED
feature in terms of performance and stability improvement.
Signed-off-by: Dmitry Osipenko <[email protected]>
---
hw/display/virtio-gpu-gl.c | 45 ++++++++++++++++++++-
hw/display/virtio-gpu-virgl.c | 74 +++++++++++++++++++++++++++++++++-
include/hw/virtio/virtio-gpu.h | 3 ++
3 files changed, 119 insertions(+), 3 deletions(-)
diff --git a/hw/display/virtio-gpu-gl.c b/hw/display/virtio-gpu-gl.c
index b640900fc6f1..23e0dd26c67b 100644
--- a/hw/display/virtio-gpu-gl.c
+++ b/hw/display/virtio-gpu-gl.c
@@ -121,7 +121,12 @@ static void virtio_gpu_gl_reset(VirtIODevice *vdev)
static void virtio_gpu_gl_device_realize(DeviceState *qdev, Error **errp)
{
ERRP_GUARD();
- VirtIOGPU *g = VIRTIO_GPU(qdev);
+ VirtIOGPUBase *b = VIRTIO_GPU_BASE(qdev);
+ VirtIOGPU *g = VIRTIO_GPU(b);
+#if !defined(CONFIG_WIN32)
+ VirtIOGPUGL *gl = VIRTIO_GPU_GL(g);
+ void *map;
+#endif
#if HOST_BIG_ENDIAN
error_setg(errp, "virgl is not supported on bigendian platforms");
@@ -152,6 +157,33 @@ static void virtio_gpu_gl_device_realize(DeviceState
*qdev, Error **errp)
#endif
virtio_gpu_device_realize(qdev, errp);
+
+ /*
+ * Check whether virtio_gpu_device_realize() failed.
+ */
+ if (*errp) {
+ return;
+ }
+
+#if !defined(CONFIG_WIN32)
+ if (virtio_gpu_hostmem_enabled(b->conf)) {
hostmem should be kept enabled for Windows. I don't have any reason to
believe hostmem does not work on Windows.
+ map = mmap(NULL, b->conf.hostmem, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
Use qemu_ram_mmap() that installs a guard page.
+ if (map == MAP_FAILED) {
+ error_setg(errp,
+ "virgl hostmem region could not be initialized: %s",
+ strerror(errno));
+ return;
+ }
+
+ gl->hostmem_mmap = map;
+ gl->hostmem_background = g_new0(MemoryRegion, 1);
Embed hostmem_background to VirtIOGPUGL and avoid having g_new0(), just
like hostmem of VirtIOGPUBase.
+ memory_region_init_ram_ptr(gl->hostmem_background, NULL,
+ "hostmem-background", b->conf.hostmem,
+ gl->hostmem_mmap);
+ memory_region_add_subregion(&b->hostmem, 0, gl->hostmem_background);
+ }
+#endif
}
static const Property virtio_gpu_gl_properties[] = {
@@ -165,6 +197,7 @@ static const Property virtio_gpu_gl_properties[] = {
static void virtio_gpu_gl_device_unrealize(DeviceState *qdev)
{
+ VirtIOGPUBase *b = VIRTIO_GPU_BASE(qdev);
VirtIOGPU *g = VIRTIO_GPU(qdev);
VirtIOGPUGL *gl = VIRTIO_GPU_GL(qdev);
@@ -187,6 +220,16 @@ static void virtio_gpu_gl_device_unrealize(DeviceState *qdev)
gl->renderer_state = RS_START;
g_array_unref(g->capset_ids);
+
+ /*
+ * It is not guaranteed that the memory region will be finalized
+ * immediately with memory_region_del_subregion(), there can be
+ * a remaining reference to gl->hostmem_mmap. VirtIO-GPU is not
+ * hotpluggable, hence no need to worry about the leaked mapping.
+ */
+ if (gl->hostmem_background) {
+ memory_region_del_subregion(&b->hostmem, gl->hostmem_background);
+ }
This memory_region_del_subregion() is unnecessary because b->hostmem and
gl->hostmem_background belong to the same device and will be gone at the
same time.
}
static void virtio_gpu_gl_class_init(ObjectClass *klass, const void *data)
diff --git a/hw/display/virtio-gpu-virgl.c b/hw/display/virtio-gpu-virgl.c
index a6860f63b563..5a663ad2acfa 100644
--- a/hw/display/virtio-gpu-virgl.c
+++ b/hw/display/virtio-gpu-virgl.c
@@ -41,9 +41,14 @@
VIRGL_VERSION_MICRO >= (micro))
#endif
+#if VIRGL_CHECK_VERSION(1, 2, 1) && !defined(CONFIG_WIN32)
+ #define VIRGL_HAS_MAP_FIXED
+#endif
Simpler:
#define VIRGL_HAS_MAP_FIXED VIRGL_CHECK_VERSION(1, 2, 1) &&
!IS_ENABLED(CONFIG_WIN32)
And you can use it like:
#if VIRGL_HAS_MAP_FIXED
+
struct virtio_gpu_virgl_resource {
struct virtio_gpu_simple_resource base;
MemoryRegion *mr;
+ void *map_fixed;
};
static struct virtio_gpu_virgl_resource *
@@ -116,6 +121,7 @@ virtio_gpu_virgl_map_resource_blob(VirtIOGPU *g,
{
struct virtio_gpu_virgl_hostmem_region *vmr;
VirtIOGPUBase *b = VIRTIO_GPU_BASE(g);
+ VirtIOGPUGL *gl = VIRTIO_GPU_GL(g);
MemoryRegion *mr;
uint64_t size;
void *data;
@@ -126,6 +132,41 @@ virtio_gpu_virgl_map_resource_blob(VirtIOGPU *g,
return -EOPNOTSUPP;
}
+#ifdef VIRGL_HAS_MAP_FIXED
+ /*
+ * virgl_renderer_resource_map_fixed() allows to create multiple
+ * mappings of the same resource, while virgl_renderer_resource_map()
+ * not. Don't allow mapping same resource twice.
+ */
+ if (res->map_fixed || res->mr) {
+ qemu_log_mask(LOG_GUEST_ERROR,
+ "%s: failed to map(fixed) virgl resource: already
mapped\n",
+ __func__);
+ return -EBUSY;
+ }
+
+ ret = virgl_renderer_resource_map_fixed(res->base.resource_id,
+ gl->hostmem_mmap + offset);
I think you need a boundary check here.
+ switch (ret) {
+ case 0:
+ res->map_fixed = gl->hostmem_mmap + offset;
+ return 0;
+
+ case -EOPNOTSUPP:
+ /*
+ * -MAP_FIXED is unsupported by this resource.
+ * Mapping falls back to a blob subregion method in that case.
+ */
+ break;
+
+ default:
+ qemu_log_mask(LOG_GUEST_ERROR,
+ "%s: failed to map(fixed) virgl resource: %s\n",
+ __func__, strerror(-ret));
+ return ret;
+ }
+#endif
+
ret = virgl_renderer_resource_map(res->base.resource_id, &data, &size);
if (ret) {
qemu_log_mask(LOG_GUEST_ERROR, "%s: failed to map virgl resource:
%s\n",
@@ -138,7 +179,7 @@ virtio_gpu_virgl_map_resource_blob(VirtIOGPU *g,
mr = &vmr->mr;
memory_region_init_ram_ptr(mr, OBJECT(mr), "blob", size, data);
- memory_region_add_subregion(&b->hostmem, offset, mr);
+ memory_region_add_subregion_overlap(gl->hostmem_background, offset, mr, 1);
This should be:
memory_region_add_subregion_overlap(&b->hostmem, offset, mr, 1);
/*
* MR could outlive the resource if MR's reference is held outside of
@@ -162,9 +203,28 @@ virtio_gpu_virgl_unmap_resource_blob(VirtIOGPU *g,
{
struct virtio_gpu_virgl_hostmem_region *vmr;
VirtIOGPUBase *b = VIRTIO_GPU_BASE(g);
+ VirtIOGPUGL *gl = VIRTIO_GPU_GL(g);
MemoryRegion *mr = res->mr;
int ret;
+#ifdef VIRGL_HAS_MAP_FIXED
+ if (res->map_fixed) {
+ res->map_fixed = mmap(res->map_fixed, res->base.blob_size,
+ PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED,
+ -1, 0);
+ if (res->map_fixed == MAP_FAILED) {
+ ret = -errno;
+ qemu_log_mask(LOG_GUEST_ERROR,
+ "%s: failed to unmap(fixed) virgl resource: %s\n",
+ __func__, strerror(-ret));
+ return ret;
This code path leaves the blob mapped but overwrites res->map_fixed with
MAP_FAILED.
Regards,
Akihiko Odaki
+ }
+
+ res->map_fixed = NULL;
+ }
+#endif
+
if (!mr) {
return 0;
}
@@ -200,7 +260,7 @@ virtio_gpu_virgl_unmap_resource_blob(VirtIOGPU *g,
b->renderer_blocked++;
/* memory region owns self res->mr object and frees it by itself */
- memory_region_del_subregion(&b->hostmem, mr);
+ memory_region_del_subregion(gl->hostmem_background, mr);
object_unparent(OBJECT(mr));
}
@@ -1265,6 +1325,16 @@ void virtio_gpu_virgl_reset_scanout(VirtIOGPU *g)
void virtio_gpu_virgl_reset(VirtIOGPU *g)
{
+#ifdef VIRGL_HAS_MAP_FIXED
+ VirtIOGPUBase *b = VIRTIO_GPU_BASE(g);
+ VirtIOGPUGL *gl = VIRTIO_GPU_GL(g);
+
+ if (gl->hostmem_mmap &&
+ mmap(gl->hostmem_mmap, b->conf.hostmem, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0) == MAP_FAILED) {
+ error_report("failed to reset virgl hostmem: %s", strerror(errno));
+ }
+#endif
virgl_renderer_reset();
virtio_gpu_virgl_reset_async_fences(g);
diff --git a/include/hw/virtio/virtio-gpu.h b/include/hw/virtio/virtio-gpu.h
index 718332284305..bfe85a4e0449 100644
--- a/include/hw/virtio/virtio-gpu.h
+++ b/include/hw/virtio/virtio-gpu.h
@@ -263,6 +263,9 @@ struct VirtIOGPUGL {
QEMUBH *async_fence_bh;
QSLIST_HEAD(, virtio_gpu_virgl_context_fence) async_fenceq;
+
+ MemoryRegion *hostmem_background;
+ void *hostmem_mmap;
};
struct VhostUserGPU {
