On Mon, Feb 06, 2023 at 10:33:13AM +0000, Matthew Auld wrote:
> On 06/02/2023 09:45, Tvrtko Ursulin wrote:
> >
> > Hi,
> >
> > Adding Matt & Thomas as potential candidates to review.
> >
> > Regards,
> >
> > Tvrtko
> >
> > On 03/02/2023 19:30, Deepak R Varma wrote:
> > > The macro definition of gen6_for_all_pdes() expands to a for loop such
> > > that it breaks when the page table is null. Hence there is no need to
> > > again test validity of the page table entry pointers in the pde list.
> > > This change is identified using itnull.cocci semantic patch.
> > >
> > > Signed-off-by: Deepak R Varma <drv@xxxxxxxxx>
> > > ---
> > > Please note: Proposed change is compile tested only.
> > >
> > > drivers/gpu/drm/i915/gt/gen6_ppgtt.c | 5 ++---
> > > 1 file changed, 2 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/gt/gen6_ppgtt.c
> > > b/drivers/gpu/drm/i915/gt/gen6_ppgtt.c
> > > index 5aaacc53fa4c..787b9e6d9f59 100644
> > > --- a/drivers/gpu/drm/i915/gt/gen6_ppgtt.c
> > > +++ b/drivers/gpu/drm/i915/gt/gen6_ppgtt.c
> > > @@ -258,8 +258,7 @@ static void gen6_ppgtt_free_pd(struct gen6_ppgtt
> > > *ppgtt)
> > > u32 pde;
> > > gen6_for_all_pdes(pt, pd, pde)
> > > - if (pt)
> > > - free_pt(&ppgtt->base.vm, pt);
> > > + free_pt(&ppgtt->base.vm, pt);
> > > }
> > > static void gen6_ppgtt_cleanup(struct i915_address_space *vm)
> > > @@ -304,7 +303,7 @@ static void pd_vma_unbind(struct
> > > i915_address_space *vm,
> > > /* Free all no longer used page tables */
> > > gen6_for_all_pdes(pt, ppgtt->base.pd, pde) {
> > > - if (!pt || atomic_read(&pt->used))
> > > + if (atomic_read(&pt->used))
>
> Wow, I was really confused trying to remember how this all works.
>
> The gen6_for_all_pdes() does:
>
> (pt = i915_pt_entry(pd, iter), true)
>
> So NULL pt is expected, and does not 'break' here, since 'true' is always
> the value that decides whether to terminate the loop. So this patch would
> lead to NULL ptr deref, AFAICT.
Hello Matt,
I understand it now. I was misreading the true as part of the function argument.
Could you please also comment if the implementation of gen6_ppgtt_free_pd() in
the same file is safe? It doesn't appear to have an check on pt validity here.
Thank you,
deepak.
>
>
>
> > > continue;
> > > free_pt(&ppgtt->base.vm, pt);
