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Wed, 04 Mar 2026 08:50:56 -0800 (PST) From: =?UTF-8?q?Alex=20Benn=C3=A9e?= To: qemu-devel@nongnu.org Cc: Peter Xu , =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= , David Hildenbrand , =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= , Markus Armbruster , Akihiko Odaki , Pierrick Bouvier , =?UTF-8?q?Alex=20Benn=C3=A9e?= , Paolo Bonzini , Eric Blake , "Michael S. Tsirkin" , Dmitry Osipenko , =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , Yiwei Zhang , Akihiko Odaki Subject: [PATCH 20/20] virtio-gpu: Support mapping hostmem blobs with map_fixed Date: Wed, 4 Mar 2026 16:50:42 +0000 Message-ID: <20260304165043.1437519-21-alex.bennee@linaro.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260304165043.1437519-1-alex.bennee@linaro.org> References: <20260304165043.1437519-1-alex.bennee@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=2a00:1450:4864:20::52e; envelope-from=alex.bennee@linaro.org; helo=mail-ed1-x52e.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @linaro.org) X-ZM-MESSAGEID: 1772643077399158500 Content-Type: text/plain; charset="utf-8" From: Dmitry Osipenko 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 Reviewed-by: Akihiko Odaki Signed-off-by: Dmitry Osipenko Message-ID: <20260303151422.977399-19-dmitry.osipenko@collabora.com> --- include/hw/virtio/virtio-gpu.h | 3 ++ hw/display/virtio-gpu-gl.c | 37 ++++++++++++++++++++- hw/display/virtio-gpu-virgl.c | 59 +++++++++++++++++++++++++++++++++- 3 files changed, 97 insertions(+), 2 deletions(-) diff --git a/include/hw/virtio/virtio-gpu.h b/include/hw/virtio/virtio-gpu.h index ec3db3b4123..f69fc194627 100644 --- a/include/hw/virtio/virtio-gpu.h +++ b/include/hw/virtio/virtio-gpu.h @@ -263,6 +263,9 @@ struct VirtIOGPUGL { =20 QEMUBH *async_fence_bh; QSLIST_HEAD(, virtio_gpu_virgl_context_fence) async_fenceq; + + MemoryRegion hostmem_background; + void *hostmem_mmap; }; =20 struct VhostUserGPU { diff --git a/hw/display/virtio-gpu-gl.c b/hw/display/virtio-gpu-gl.c index 8b71dd6fc26..2b7a41c4664 100644 --- a/hw/display/virtio-gpu-gl.c +++ b/hw/display/virtio-gpu-gl.c @@ -13,6 +13,7 @@ =20 #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" @@ -106,7 +107,12 @@ static void virtio_gpu_gl_reset(VirtIODevice *vdev) static void virtio_gpu_gl_device_realize(DeviceState *qdev, Error **errp) { ERRP_GUARD(); - VirtIOGPU *g =3D VIRTIO_GPU(qdev); + VirtIOGPUBase *b =3D VIRTIO_GPU_BASE(qdev); + VirtIOGPU *g =3D VIRTIO_GPU(b); +#if !defined(CONFIG_WIN32) + VirtIOGPUGL *gl =3D VIRTIO_GPU_GL(g); + void *map; +#endif =20 #if HOST_BIG_ENDIAN 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) g->parent_obj.conf.flags |=3D 1 << VIRTIO_GPU_FLAG_CONTEXT_INIT_ENABLE= D; #endif =20 +#if !defined(CONFIG_WIN32) + if (virtio_gpu_hostmem_enabled(b->conf)) { + map =3D qemu_ram_mmap(-1, b->conf.hostmem, qemu_real_host_page_siz= e(), + 0, 0); + if (map =3D=3D MAP_FAILED) { + error_setg_errno(errp, errno, + "virgl hostmem region could not be initialize= d"); + return; + } + + gl->hostmem_mmap =3D 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_backgroun= d); + } +#endif + virtio_gpu_device_realize(qdev, errp); } =20 @@ -172,6 +196,17 @@ static void virtio_gpu_gl_device_unrealize(DeviceState= *qdev) gl->renderer_state =3D RS_START; =20 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 unnecess= ary + * because b->hostmem and gl->hostmem_background belong to the same + * device and will be gone at the same time. + */ } =20 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 1819f9cb7e9..b7a2d160ddd 100644 --- a/hw/display/virtio-gpu-virgl.c +++ b/hw/display/virtio-gpu-virgl.c @@ -41,9 +41,13 @@ VIRGL_VERSION_MICRO >=3D (micro)) #endif =20 +#define VIRGL_HAS_MAP_FIXED \ + (VIRGL_CHECK_VERSION(1, 3, 0) && !IS_ENABLED(CONFIG_WIN32)) + struct virtio_gpu_virgl_resource { struct virtio_gpu_simple_resource base; MemoryRegion *mr; + void *map_fixed; }; =20 static struct virtio_gpu_virgl_resource * @@ -155,6 +159,9 @@ virtio_gpu_virgl_map_resource_blob(VirtIOGPU *g, g_autofree char *name =3D NULL; struct virtio_gpu_virgl_hostmem_region *vmr; VirtIOGPUBase *b =3D VIRTIO_GPU_BASE(g); +#if VIRGL_HAS_MAP_FIXED + VirtIOGPUGL *gl =3D VIRTIO_GPU_GL(g); +#endif MemoryRegion *mr; uint64_t size; void *data; @@ -165,6 +172,41 @@ virtio_gpu_virgl_map_resource_blob(VirtIOGPU *g, return -EOPNOTSUPP; } =20 +#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 ma= pped\n", + __func__); + return -EBUSY; + } + + ret =3D virgl_renderer_resource_map_fixed(res->base.resource_id, + gl->hostmem_mmap + offset); + switch (ret) { + case 0: + res->map_fixed =3D 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 =3D virgl_renderer_resource_map(res->base.resource_id, &data, &siz= e); if (ret) { 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, =20 mr =3D &vmr->mr; memory_region_init_ram_ptr(mr, OBJECT(vmr), "mr", size, data); - memory_region_add_subregion(&b->hostmem, offset, mr); + memory_region_add_subregion_overlap(&b->hostmem, offset, mr, 1); =20 res->mr =3D mr; =20 @@ -200,6 +242,21 @@ virtio_gpu_virgl_unmap_resource_blob(VirtIOGPU *g, MemoryRegion *mr =3D res->mr; int ret; =20 +#if VIRGL_HAS_MAP_FIXED + if (res->map_fixed) { + if (mmap(res->map_fixed, res->base.blob_size, PROT_READ | PROT_WRI= TE, + MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, + -1, 0) =3D=3D MAP_FAILED) { + ret =3D -errno; + error_report("%s: failed to unmap(fixed) virgl resource: %s", + __func__, strerror(-ret)); + return ret; + } + + res->map_fixed =3D NULL; + } +#endif + if (!mr) { return 0; } --=20 2.47.3