On Tue, Aug 6, 2024 at 9:15 AM Gurchetan Singh <gurchetansingh@xxxxxxxxxxxx> wrote: > > > > On Mon, Aug 5, 2024 at 2:14 AM Sergio Lopez Pascual <slp@xxxxxxxxxx> wrote: >> >> Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> 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. BR, -R >> >> >> Thanks, >> Sergio. >>
