From b2a8116e25923643e9613ac5b65dd6e78dc5ee77 Mon Sep 17 00:00:00 2001 From: Daniel Vetter Date: Mon, 4 Nov 2019 18:37:59 +0100 Subject: [PATCH] dma_resv: prime lockdep annotations MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Full audit of everyone: - i915, radeon, amdgpu should be clean per their maintainers. - vram helpers should be fine, they don't do command submission, so really no business holding struct_mutex while doing copy_*_user. But I haven't checked them all. - panfrost seems to dma_resv_lock only in panfrost_job_push, which looks clean. - v3d holds dma_resv locks in the tail of its v3d_submit_cl_ioctl(), copying from/to userspace happens all in v3d_lookup_bos which is outside of the critical section. - vmwgfx has a bunch of ioctls that do their own copy_*_user: - vmw_execbuf_process: First this does some copies in vmw_execbuf_cmdbuf() and also in the vmw_execbuf_process() itself. Then comes the usual ttm reserve/validate sequence, then actual submission/fencing, then unreserving, and finally some more copy_to_user in vmw_execbuf_copy_fence_user. Glossing over tons of details, but looks all safe. - vmw_fence_event_ioctl: No ttm_reserve/dma_resv_lock anywhere to be seen, seems to only create a fence and copy it out. - a pile of smaller ioctl in vmwgfx_ioctl.c, no reservations to be found there. Summary: vmwgfx seems to be fine too. - virtio: There's virtio_gpu_execbuffer_ioctl, which does all the copying from userspace before even looking up objects through their handles, so safe. Plus the getparam/getcaps ioctl, also both safe. - qxl only has qxl_execbuffer_ioctl, which calls into qxl_process_single_command. There's a lovely comment before the __copy_from_user_inatomic that the slowpath should be copied from i915, but I guess that never happened. Try not to be unlucky and get your CS data evicted between when it's written and the kernel tries to read it. The only other copy_from_user is for relocs, but those are done before qxl_release_reserve_list(), which seems to be the only thing reserving buffers (in the ttm/dma_resv sense) in that code. So looks safe. - A debugfs file in nouveau_debugfs_pstate_set() and the usif ioctl in usif_ioctl() look safe. nouveau_gem_ioctl_pushbuf() otoh breaks this everywhere and needs to be fixed up. v2: Thomas pointed at that vmwgfx calls dma_resv_init while it holds a dma_resv lock of a different object already. Christian mentioned that ttm core does this too for ghost objects. intel-gfx-ci highlighted that i915 has similar issues. Unfortunately we can't do this in the usual module init functions, because kernel threads don't have an ->mm - we have to wait around for some user thread to do this. Solution is to spawn a worker (but only once). It's horrible, but it works. v3: We can allocate mm! (Chris). Horrible worker hack out, clean initcall solution in. v4: Annotate with __init (Rob Herring) Cc: Rob Herring Cc: Alex Deucher Cc: Christian König Cc: Chris Wilson Cc: Thomas Zimmermann Cc: Rob Herring Cc: Tomeu Vizoso Cc: Eric Anholt Cc: Dave Airlie Cc: Gerd Hoffmann Cc: Ben Skeggs Cc: "VMware Graphics" Cc: Thomas Hellstrom Reviewed-by: Thomas Hellstrom Reviewed-by: Christian König Reviewed-by: Chris Wilson Tested-by: Chris Wilson Signed-off-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20191104173801.2972-1-daniel.vetter@ffwll.ch --- drivers/dma-buf/dma-resv.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c index 709002515550..a05ff542be22 100644 --- a/drivers/dma-buf/dma-resv.c +++ b/drivers/dma-buf/dma-resv.c @@ -34,6 +34,7 @@ #include #include +#include /** * DOC: Reservation Object Overview @@ -95,6 +96,29 @@ static void dma_resv_list_free(struct dma_resv_list *list) kfree_rcu(list, rcu); } +#if IS_ENABLED(CONFIG_LOCKDEP) +static void __init dma_resv_lockdep(void) +{ + struct mm_struct *mm = mm_alloc(); + struct dma_resv obj; + + if (!mm) + return; + + dma_resv_init(&obj); + + down_read(&mm->mmap_sem); + ww_mutex_lock(&obj.lock, NULL); + fs_reclaim_acquire(GFP_KERNEL); + fs_reclaim_release(GFP_KERNEL); + ww_mutex_unlock(&obj.lock); + up_read(&mm->mmap_sem); + + mmput(mm); +} +subsys_initcall(dma_resv_lockdep); +#endif + /** * dma_resv_init - initialize a reservation object * @obj: the reservation object