[PATCH] dma_resv: prime lockdep annotations

[Rob Herring]

On Thu, Aug 22, 2019 at 1:55 AM Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
>
> 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.
>
> Cc: Alex Deucher <alexander.deucher at amd.com>
> Cc: Christian König <christian.koenig at amd.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Thomas Zimmermann <tzimmermann at suse.de>
> Cc: Rob Herring <robh at kernel.org>
> Cc: Tomeu Vizoso <tomeu.vizoso at collabora.com>
> Cc: Eric Anholt <eric at anholt.net>
> Cc: Dave Airlie <airlied at redhat.com>
> Cc: Gerd Hoffmann <kraxel at redhat.com>
> Cc: Ben Skeggs <bskeggs at redhat.com>
> Cc: "VMware Graphics" <linux-graphics-maintainer at vmware.com>
> Cc: Thomas Hellstrom <thellstrom at vmware.com>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> ---
>  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 42a8f3f11681..d233ef4cf0d7 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 +96,29 @@ static void dma_resv_list_free(struct dma_resv_list *list)
>         kfree_rcu(list, rcu);
>  }
>
> +#if IS_ENABLED(CONFIG_LOCKDEP)
> +static void dma_resv_lockdep(void)

__init

> +{
> +       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
> --
> 2.23.0.rc1
>