Quoting Daniel Vetter (2019-08-21 22:50:28)
> 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.
>
> Cc: Alex Deucher <alexander.deucher@xxxxxxx>
> Cc: Christian König <christian.koenig@xxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
> Cc: Rob Herring <robh@xxxxxxxxxx>
> Cc: Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx>
> Cc: Eric Anholt <eric@xxxxxxxxxx>
> Cc: Dave Airlie <airlied@xxxxxxxxxx>
> Cc: Gerd Hoffmann <kraxel@xxxxxxxxxx>
> Cc: Ben Skeggs <bskeggs@xxxxxxxxxx>
> Cc: "VMware Graphics" <linux-graphics-maintainer@xxxxxxxxxx>
> Cc: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> ---
> drivers/dma-buf/dma-resv.c | 42 ++++++++++++++++++++++++++++++++++++++
> 1 file changed, 42 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
> index 42a8f3f11681..29988b1564c1 100644
> --- a/drivers/dma-buf/dma-resv.c
> +++ b/drivers/dma-buf/dma-resv.c
> @@ -34,6 +34,7 @@
>
> #include <linux/dma-resv.h>
> #include <linux/export.h>
> +#include <linux/sched/mm.h>
>
> /**
> * DOC: Reservation Object Overview
> @@ -95,6 +96,28 @@ static void dma_resv_list_free(struct dma_resv_list *list)
> kfree_rcu(list, rcu);
> }
>
> +#if IS_ENABLED(CONFIG_LOCKDEP)
> +struct lockdep_work {
> + struct work_struct work;
> + struct dma_resv obj;
> + struct mm_struct *mm;
> +} lockdep_work;
> +
> +void lockdep_work_fn(struct work_struct *work)
> +{
> + dma_resv_init(&lockdep_work.obj);
> +
> + down_read(&lockdep_work.mm->mmap_sem);
> + ww_mutex_lock(&lockdep_work.obj.lock, NULL);
> + fs_reclaim_acquire(GFP_KERNEL);
> + fs_reclaim_release(GFP_KERNEL);
> + ww_mutex_unlock(&lockdep_work.obj.lock);
> + up_read(&lockdep_work.mm->mmap_sem);
> +
> + mmput(lockdep_work.mm);
> +}
> +#endif
#if IS_ENABLED(CONFIG_LOCKDEP)
static void dma_resv_lockmap(void)
{
struct mm_struct *mm = alloc_mm();
struct dma_resv obj;
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);
}
core_initcall(dma_resv_lockmap);
#endif
as a thought.
-Chris
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