On 2025/11/25 11:35, 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.
Tested-by: Yiwei Zhang <[email protected]>
Signed-off-by: Dmitry Osipenko <[email protected]>
---
hw/display/virtio-gpu-gl.c | 41 +++++++++++++++++++++++-
hw/display/virtio-gpu-virgl.c | 58 +++++++++++++++++++++++++++++++++-
include/hw/virtio/virtio-gpu.h | 3 ++
3 files changed, 100 insertions(+), 2 deletions(-)
diff --git a/hw/display/virtio-gpu-gl.c b/hw/display/virtio-gpu-gl.c
index d65da4863923..8a7a33946085 100644
--- a/hw/display/virtio-gpu-gl.c
+++ b/hw/display/virtio-gpu-gl.c
@@ -13,6 +13,7 @@
#include "qemu/osdep.h"
#include "qemu/iov.h"
+#include "qemu/mmap-alloc.h"
#include "qemu/module.h"
#include "qemu/error-report.h"
#include "qapi/error.h"
@@ -124,7 +125,12 @@ 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");
@@ -155,6 +161,28 @@ static void virtio_gpu_gl_device_realize(DeviceState
*qdev, Error **errp)
#endif
virtio_gpu_device_realize(qdev, errp);
+ if (*errp) {
+ return;
+ }
+
+#if !defined(CONFIG_WIN32)
+ if (virtio_gpu_hostmem_enabled(b->conf)) {
+ map = qemu_ram_mmap(-1, b->conf.hostmem, qemu_real_host_page_size(),
+ 0, 0);
+ if (map == MAP_FAILED) {
+ error_setg(errp,
+ "virgl hostmem region could not be initialized: %s",
+ strerror(errno));
error_setg_errno() will make this a bit simpler.
+ return;
+ }
+
+ gl->hostmem_mmap = map;
+ 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[] = {
@@ -190,6 +218,17 @@ 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.
+ *
+ * The memory_region_del_subregion(gl->hostmem_background) 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 9b36b378c2fd..987980e8a49d 100644
--- a/hw/display/virtio-gpu-virgl.c
+++ b/hw/display/virtio-gpu-virgl.c
@@ -41,9 +41,13 @@
VIRGL_VERSION_MICRO >= (micro))
#endif
+#define VIRGL_HAS_MAP_FIXED \
+ (VIRGL_CHECK_VERSION(1, 2, 1) && !IS_ENABLED(CONFIG_WIN32))
+
struct virtio_gpu_virgl_resource {
struct virtio_gpu_simple_resource base;
MemoryRegion *mr;
+ void *map_fixed;
};
static struct virtio_gpu_virgl_resource *
@@ -116,6 +120,9 @@ virtio_gpu_virgl_map_resource_blob(VirtIOGPU *g,
{
struct virtio_gpu_virgl_hostmem_region *vmr;
VirtIOGPUBase *b = VIRTIO_GPU_BASE(g);
+#if VIRGL_HAS_MAP_FIXED
+ VirtIOGPUGL *gl = VIRTIO_GPU_GL(g);
+#endif
MemoryRegion *mr;
uint64_t size;
void *data;
@@ -134,6 +141,41 @@ virtio_gpu_virgl_map_resource_blob(VirtIOGPU *g,
return -EINVAL;
}
+#if 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);
+ 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 -1;
+ }
+#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",
@@ -146,7 +188,7 @@ 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(&b->hostmem, offset, mr, 1);
/*
* MR could outlive the resource if MR's reference is held outside of
@@ -173,6 +215,20 @@ virtio_gpu_virgl_unmap_resource_blob(VirtIOGPU *g,
MemoryRegion *mr = res->mr;
int ret;
+#if VIRGL_HAS_MAP_FIXED
+ if (res->map_fixed) {
+ if (mmap(res->map_fixed, res->base.blob_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED,
+ -1, 0) == MAP_FAILED) {
+ error_report("%s: failed to unmap(fixed) virgl resource: %s",
+ __func__, strerror(errno));
+ return -1;
+ }
+
+ res->map_fixed = NULL;
+ }
+#endif
+
if (!mr) {
return 0;
}
diff --git a/include/hw/virtio/virtio-gpu.h b/include/hw/virtio/virtio-gpu.h
index 9e1473d1bb66..420c6e2a2515 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 {
