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Tsirkin" , Paolo Bonzini , Yiwei Zhang , Sergio Lopez Pascual Cc: Gert Wollny , qemu-devel@nongnu.org, Gurchetan Singh , Alyssa Ross , =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= , Alex Deucher , Stefano Stabellini , =?UTF-8?q?Christian=20K=C3=B6nig?= , Xenia Ragiadakou , Honglei Huang , Julia Zhang , Chen Jiqian , Rob Clark , Robert Beckett Subject: [RFC PATCH v3 7/7] virtio-gpu: Support mapping hostmem blobs with map_fixed Date: Thu, 20 Nov 2025 07:06:32 +0300 Message-ID: <20251120040632.4036204-8-dmitry.osipenko@collabora.com> X-Mailer: git-send-email 2.51.1 In-Reply-To: <20251120040632.4036204-1-dmitry.osipenko@collabora.com> References: <20251120040632.4036204-1-dmitry.osipenko@collabora.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ZohoMailClient: External 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=136.143.184.112; envelope-from=dmitry.osipenko@collabora.com; helo=sender3-pp-f112.zoho.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_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, 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: 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 dmitry.osipenko@collabora.com) X-ZM-MESSAGEID: 1763611766596018900 Content-Type: text/plain; charset="utf-8" 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 Signed-off-by: Dmitry Osipenko --- 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 @@ =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" @@ -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 =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"); @@ -155,6 +161,30 @@ static void virtio_gpu_gl_device_realize(DeviceState *= qdev, Error **errp) #endif =20 virtio_gpu_device_realize(qdev, errp); + + /* + * Check whether virtio_gpu_device_realize() failed. + */ + if (*errp) { + return; + } + + 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(errp, + "virgl hostmem region could not be initialized: %s", + strerror(errno)); + 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); + } } =20 static const Property virtio_gpu_gl_properties[] =3D { @@ -190,6 +220,17 @@ 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 35201d629b9c..2bd0ed6227cf 100644 --- a/hw/display/virtio-gpu-virgl.c +++ b/hw/display/virtio-gpu-virgl.c @@ -41,9 +41,12 @@ VIRGL_VERSION_MICRO >=3D (micro)) #endif =20 +#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; }; =20 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 =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; @@ -134,6 +140,41 @@ virtio_gpu_virgl_map_resource_blob(VirtIOGPU *g, return -1; } =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 -1; + } + + 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 -1; + } +#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", @@ -146,7 +187,7 @@ virtio_gpu_virgl_map_resource_blob(VirtIOGPU *g, =20 mr =3D &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); =20 /* * 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 =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) { + error_report("%s: failed to unmap(fixed) virgl resource: %s", + __func__, strerror(errno)); + return -1; + } + + res->map_fixed =3D 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 { =20 QEMUBH *async_fence_bh; QSLIST_HEAD(, virtio_gpu_virgl_context_fence) async_fenceq; + + MemoryRegion hostmem_background; + void *hostmem_mmap; }; =20 struct VhostUserGPU { --=20 2.51.1