virtio-gpu: Support mapping hostmem blobs with map_fixed
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> Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Message-ID: <20260303151422.977399-19-dmitry.osipenko@collabora.com> Message-ID: <20260304165043.1437519-21-alex.bennee@linaro.org> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Dmitry Osipenko committed
Mar 4, 2026 at 16:50 UTC
4eb0aace85f507e21bb8ac323ad81c5860f7a52d
3 files changed
+97
-2
hw/display/virtio-gpu-gl.c
+36
-1
@@ -13,6 +13,7 @@
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#include "qemu/osdep.h"
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#include "qemu/iov.h"
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+#include "qemu/mmap-alloc.h"
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#include "qemu/module.h"
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#include "qemu/error-report.h"
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#include "qapi/error.h"
@@ -106,7 +107,12 @@ static void virtio_gpu_gl_reset(VirtIODevice *vdev)
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static void virtio_gpu_gl_device_realize(DeviceState *qdev, Error **errp)
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{
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ERRP_GUARD();
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- VirtIOGPU *g = VIRTIO_GPU(qdev);
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+ VirtIOGPUBase *b = VIRTIO_GPU_BASE(qdev);
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+ VirtIOGPU *g = VIRTIO_GPU(b);
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+#if !defined(CONFIG_WIN32)
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+ VirtIOGPUGL *gl = VIRTIO_GPU_GL(g);
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+ void *map;
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+#endif
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#if HOST_BIG_ENDIAN
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error_setg(errp, "virgl is not supported on bigendian platforms");
@@ -136,6 +142,24 @@ static void virtio_gpu_gl_device_realize(DeviceState *qdev, Error **errp)
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g->parent_obj.conf.flags |= 1 << VIRTIO_GPU_FLAG_CONTEXT_INIT_ENABLED;
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#endif
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+#if !defined(CONFIG_WIN32)
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+ if (virtio_gpu_hostmem_enabled(b->conf)) {
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+ map = qemu_ram_mmap(-1, b->conf.hostmem, qemu_real_host_page_size(),
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+ 0, 0);
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+ if (map == MAP_FAILED) {
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+ error_setg_errno(errp, errno,
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+ "virgl hostmem region could not be initialized");
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+ return;
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+ }
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+
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+ gl->hostmem_mmap = map;
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+ memory_region_init_ram_ptr(&gl->hostmem_background, NULL,
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+ "hostmem-background", b->conf.hostmem,
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+ gl->hostmem_mmap);
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+ memory_region_add_subregion(&b->hostmem, 0, &gl->hostmem_background);
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+ }
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+#endif
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+
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virtio_gpu_device_realize(qdev, errp);
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}
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@@ -172,6 +196,17 @@ static void virtio_gpu_gl_device_unrealize(DeviceState *qdev)
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gl->renderer_state = RS_START;
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g_array_unref(g->capset_ids);
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+
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+ /*
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+ * It is not guaranteed that the memory region will be finalized
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+ * immediately with memory_region_del_subregion(), there can be
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+ * a remaining reference to gl->hostmem_mmap. VirtIO-GPU is not
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+ * hotpluggable, hence no need to worry about the leaked mapping.
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+ *
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+ * The memory_region_del_subregion(gl->hostmem_background) is unnecessary
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+ * because b->hostmem and gl->hostmem_background belong to the same
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+ * device and will be gone at the same time.
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+ */
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}
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static void virtio_gpu_gl_class_init(ObjectClass *klass, const void *data)
hw/display/virtio-gpu-virgl.c
+58
-1
@@ -41,9 +41,13 @@
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VIRGL_VERSION_MICRO >= (micro))
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#endif
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+#define VIRGL_HAS_MAP_FIXED \
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+ (VIRGL_CHECK_VERSION(1, 3, 0) && !IS_ENABLED(CONFIG_WIN32))
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+
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struct virtio_gpu_virgl_resource {
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struct virtio_gpu_simple_resource base;
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MemoryRegion *mr;
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+ void *map_fixed;
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};
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static struct virtio_gpu_virgl_resource *
@@ -155,6 +159,9 @@ virtio_gpu_virgl_map_resource_blob(VirtIOGPU *g,
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g_autofree char *name = NULL;
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struct virtio_gpu_virgl_hostmem_region *vmr;
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VirtIOGPUBase *b = VIRTIO_GPU_BASE(g);
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+#if VIRGL_HAS_MAP_FIXED
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+ VirtIOGPUGL *gl = VIRTIO_GPU_GL(g);
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+#endif
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MemoryRegion *mr;
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uint64_t size;
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void *data;
@@ -165,6 +172,41 @@ virtio_gpu_virgl_map_resource_blob(VirtIOGPU *g,
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return -EOPNOTSUPP;
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}
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+#if VIRGL_HAS_MAP_FIXED
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+ /*
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+ * virgl_renderer_resource_map_fixed() allows to create multiple
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+ * mappings of the same resource, while virgl_renderer_resource_map()
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+ * not. Don't allow mapping same resource twice.
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+ */
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+ if (res->map_fixed || res->mr) {
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+ qemu_log_mask(LOG_GUEST_ERROR,
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+ "%s: failed to map(fixed) virgl resource: already mapped\n",
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+ __func__);
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+ return -EBUSY;
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+ }
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+
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+ ret = virgl_renderer_resource_map_fixed(res->base.resource_id,
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+ gl->hostmem_mmap + offset);
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+ switch (ret) {
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+ case 0:
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+ res->map_fixed = gl->hostmem_mmap + offset;
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+ return 0;
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+
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+ case -EOPNOTSUPP:
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+ /*
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+ * MAP_FIXED is unsupported by this resource.
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+ * Mapping falls back to a blob subregion method in that case.
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+ */
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+ break;
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+
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+ default:
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+ qemu_log_mask(LOG_GUEST_ERROR,
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+ "%s: failed to map(fixed) virgl resource: %s\n",
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+ __func__, strerror(-ret));
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+ return ret;
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+ }
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+#endif
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+
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ret = virgl_renderer_resource_map(res->base.resource_id, &data, &size);
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if (ret) {
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qemu_log_mask(LOG_GUEST_ERROR, "%s: failed to map virgl resource: %s\n",
@@ -181,7 +223,7 @@ virtio_gpu_virgl_map_resource_blob(VirtIOGPU *g,
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mr = &vmr->mr;
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memory_region_init_ram_ptr(mr, OBJECT(vmr), "mr", size, data);
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- memory_region_add_subregion(&b->hostmem, offset, mr);
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+ memory_region_add_subregion_overlap(&b->hostmem, offset, mr, 1);
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res->mr = mr;
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@@ -200,6 +242,21 @@ virtio_gpu_virgl_unmap_resource_blob(VirtIOGPU *g,
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MemoryRegion *mr = res->mr;
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int ret;
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+#if VIRGL_HAS_MAP_FIXED
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+ if (res->map_fixed) {
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+ if (mmap(res->map_fixed, res->base.blob_size, PROT_READ | PROT_WRITE,
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+ MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED,
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+ -1, 0) == MAP_FAILED) {
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+ ret = -errno;
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+ error_report("%s: failed to unmap(fixed) virgl resource: %s",
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+ __func__, strerror(-ret));
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+ return ret;
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+ }
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+
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+ res->map_fixed = NULL;
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+ }
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+#endif
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+
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if (!mr) {
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return 0;
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}
include/hw/virtio/virtio-gpu.h
+3
@@ -263,6 +263,9 @@ struct VirtIOGPUGL {
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QEMUBH *async_fence_bh;
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QSLIST_HEAD(, virtio_gpu_virgl_context_fence) async_fenceq;
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+
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+ MemoryRegion hostmem_background;
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+ void *hostmem_mmap;
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};
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struct VhostUserGPU {