On Tue, Aug 6, 2024 at 1:15 PM Rob Clark <robdcl...@gmail.com> wrote:
> On Tue, Aug 6, 2024 at 9:15 AM Gurchetan Singh > <gurchetansi...@chromium.org> wrote: > > > > > > > > On Mon, Aug 5, 2024 at 2:14 AM Sergio Lopez Pascual <s...@redhat.com> > wrote: > >> > >> Dmitry Osipenko <dmitry.osipe...@collabora.com> writes: > >> > >> > On 7/23/24 14:49, Sergio Lopez wrote: > >> >> There's an incresing number of machines supporting multiple page > sizes > >> >> and on these machines the host and a guest can be running, each one, > >> >> with a different page size. > >> >> > >> >> For what pertains to virtio-gpu, this is not a problem if the page > size > >> >> of the guest happens to be bigger or equal than the host, but will > >> >> potentially lead to failures in memory allocations and/or mappings > >> >> otherwise. > >> > > >> > Please describe concrete problem you're trying to solve. Guest memory > >> > allocation consists of guest pages, I don't see how knowledge of host > >> > page size helps anything in userspace. > >> > > >> > I suspect you want this for host blobs, but then it should be > >> > virtio_gpu_vram_create() that should use max(host_page_sz, > >> > guest_page_size), AFAICT. It's kernel who is responsible for memory > >> > management, userspace can't be trusted for doing that. > >> > >> Mesa's Vulkan/Venus uses CREATE_BLOB to request the host the creation > >> and mapping into the guest of device-backed memory and shmem regions. > >> The CREATE_BLOB ioctl doesn't update drm_virtgpu_resource_create->size, > >> so the guest kernel (and, as a consequence, the host kernel) can't > >> override the user's request. > >> > >> I'd like Mesa's Vulkan/Venus in the guest to be able to obtain the host > >> page size to align the size of the CREATE_BLOB requests as required. > > > > > > gfxstream solves this problem by putting the relevant information in the > capabilities obtained from the host: > > > > > https://android.googlesource.com/platform/hardware/google/gfxstream/+/refs/heads/main/host/virtio-gpu-gfxstream-renderer.cpp#1691 > > > > If you want to be paranoid, you can also validate the > ResourceCreateBlob::size is properly host-page aligned when that request > reaches the host. > > > > So you can probably solve this problem using current interfaces. > Whether it's cleaner for all context types to use the capabilities, or have > all VMMs to expose VIRTIO_GPU_F_HOST_PAGE_SIZE, would be the cost/benefit > tradeoff. > > > > I guess solving it in a context-type specific way is possible. But I > think it is a relatively universal constraint. And maybe it makes > sense for virtgpu guest kernel to enforce alignment (at least it can > return an error synchronously) in addition to the host. > virtio-media may have support for VIRTIO_MEDIA_CMD_MMAP too, so could run into this issue. https://github.com/chromeos/virtio-media?tab=readme-ov-file#shared-memory-regions virtio-fs also has the DAX window which uses the same memory mapping mechanism. https://virtio-fs.gitlab.io/design.html Maybe this should not be a virtio-gpu thing, but a virtio thing? > > BR, > -R > > >> > >> > >> Thanks, > >> Sergio. > >> >
