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 <zzyiwei@gmail.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
hw/display/virtio-gpu-gl.c | 43 ++++++++++++++++++++++++-
hw/display/virtio-gpu-virgl.c | 57 +++++++++++++++++++++++++++++++++-
include/hw/virtio/virtio-gpu.h | 3 ++
3 files changed, 101 insertions(+), 2 deletions(-)
diff --git a/hw/display/virtio-gpu-gl.c b/hw/display/virtio-gpu-gl.c
index d65da4863923..097f3ce4cb71 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 +161,30 @@ 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 (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));
+ 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);
+ }
}
static const Property virtio_gpu_gl_properties[] = {
@@ -190,6 +220,17 @@ 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 35201d629b9c..2bd0ed6227cf 100644
--- a/hw/display/virtio-gpu-virgl.c
+++ b/hw/display/virtio-gpu-virgl.c
@@ -41,9 +41,12 @@
VIRGL_VERSION_MICRO >= (micro))
#endif
+#define VIRGL_HAS_MAP_FIXED VIRGL_CHECK_VERSION(1, 2, 1)
+
struct virtio_gpu_virgl_resource {
struct virtio_gpu_simple_resource base;
MemoryRegion *mr;
+ void *map_fixed;
};
static struct virtio_gpu_virgl_resource *
@@ -116,6 +119,9 @@ 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 +140,41 @@ virtio_gpu_virgl_map_resource_blob(VirtIOGPU *g,
return -1;
}
+#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 -1;
+ }
+
+ 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 +187,7 @@ 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 +214,20 @@ 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 {
--
2.51.1On 2025/11/20 13:06, 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 <zzyiwei@gmail.com>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> ---
> hw/display/virtio-gpu-gl.c | 43 ++++++++++++++++++++++++-
> hw/display/virtio-gpu-virgl.c | 57 +++++++++++++++++++++++++++++++++-
> include/hw/virtio/virtio-gpu.h | 3 ++
> 3 files changed, 101 insertions(+), 2 deletions(-)
>
> diff --git a/hw/display/virtio-gpu-gl.c b/hw/display/virtio-gpu-gl.c
> index d65da4863923..097f3ce4cb71 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 +161,30 @@ 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.
> + */
It is obvious so this comment is unnecessary.
> + if (*errp) {
> + return;
> + }
> +
> + if (virtio_gpu_hostmem_enabled(b->conf)) {
> + map = qemu_ram_mmap(-1, b->conf.hostmem, qemu_real_host_page_size(),
> + 0, 0);
qemu_ram_mmap() shouldn't be called if !defined(CONFIG_WIN32).
> + if (map == MAP_FAILED) {
> + error_setg(errp,
> + "virgl hostmem region could not be initialized: %s",
> + strerror(errno));
> + 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);
> + }
> }
>
> static const Property virtio_gpu_gl_properties[] = {
> @@ -190,6 +220,17 @@ 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 35201d629b9c..2bd0ed6227cf 100644
> --- a/hw/display/virtio-gpu-virgl.c
> +++ b/hw/display/virtio-gpu-virgl.c
> @@ -41,9 +41,12 @@
> VIRGL_VERSION_MICRO >= (micro))
> #endif
>
> +#define VIRGL_HAS_MAP_FIXED VIRGL_CHECK_VERSION(1, 2, 1)
> +
> struct virtio_gpu_virgl_resource {
> struct virtio_gpu_simple_resource base;
> MemoryRegion *mr;
> + void *map_fixed;
> };
>
> static struct virtio_gpu_virgl_resource *
> @@ -116,6 +119,9 @@ 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 +140,41 @@ virtio_gpu_virgl_map_resource_blob(VirtIOGPU *g,
> return -1;
> }
>
> +#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 -1;
> + }
> +
> + 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 +187,7 @@ 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 +214,20 @@ 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 {
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