[Intel-gfx] [PATCH] dma_resv: prime lockdep annotations

[Daniel Vetter]

On Thu, Aug 22, 2019 at 07:53:53AM +0000, Koenig, Christian wrote:
> Am 22.08.19 um 08:54 schrieb Daniel Vetter:
> > 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>
> 
> Reviewed-by: Christian König <christian.koenig at amd.com>

Did you get a chance to give this a spin on the amd CI?
-Daniel

> 
> > ---
> >   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)
> > +{
> > +	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
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch