Hi list,
virtio-gpu is moving in the direction where BO pages are pinned for the lifetime for simplicity. I am wondering if that is considered a security issue in general, especially after running into the description of the new DMABUF_MOVE_NOTIFY config option.
Most drivers do not have a shrinker, or whether a BO is purgeable is entirely controlled by the userspace (madvice). They can be categorized as "a security problem where userspace is able to pin unrestricted amounts of memory". But those drivers are normally found on systems without swap. I don't think the issue applies.
Of the desktop GPU drivers, i915's shrinker certainly supports purging to swap. TTM is a bit hard to follow. I can't really tell if amdgpu or nouveau supports that. virtio-gpu is more commonly found on systems with swaps so I think it should follow the desktop practices?
Truth is, the emulated virtio-gpu device always supports page moves with VIRTIO_GPU_CMD_RESOURCE_{ATTACH,DETACH}_BACKING. It is just that the driver does not make use of them. That makes this less of an issue because the driver can be fixed anytime (finger crossed that the emulator won't have bugs in these untested paths). This issue becomes more urgent because we are considering adding a new HW command[1] where page moves will be disallowed. We definitely don't want a HW command that is inherently insecure, if BO pages pinned for the lifetime is considered a security issue on desktops.
[1] VIRTIO_GPU_CMD_RESOURCE_CREATE_BLOB https://gitlab.freedesktop.org/virgl/drm-misc-next/-/blob/virtio-gpu-next/in...