[PATCH] drm/amdgpu: fix an underflow on non-4KB-page systems

[Xi Ruoyao]

On 2021-03-29 20:04 +0200, Christian König wrote:
> Am 29.03.21 um 19:53 schrieb Xℹ Ruoyao:
> > If the initial value of `num_entires` (calculated at line 1654) is not
> > an integral multiple of `AMDGPU_GPU_PAGES_IN_CPU_PAGE`, in line 1681 a
> > value greater than the initial value will be assigned to it.  That causes
> > `start > last + 1` after line 1708.  Then in the next iteration an
> > underflow happens at line 1654.  It causes message
> > 
> >      *ERROR* Couldn't update BO_VA (-12)
> > 
> > printed in kernel log, and GPU hanging.
> > 
> > Fortify the criteria of the loop to fix this issue.
> 
> NAK the value of num_entries must always be a multiple of 
> AMDGPU_GPU_PAGES_IN_CPU_PAGE or otherwise we corrupt the page tables.
> 
> How do you trigger that?

Simply run "OpenGL area" from gtk3-demo (which just renders a triangle with GL)
under Xorg, on MIPS64.  See the BugLink.

> Christian.
> 
> > 
> > BugLink: https://gitlab.freedesktop.org/drm/amd/-/issues/1549
> > Fixes: a39f2a8d7066 ("drm/amdgpu: nuke amdgpu_vm_bo_split_mapping v2")
> > Reported-by: Xi Ruoyao <xry111 at mengyan1223.wang>
> > Reported-by: Dan Horák <dan at danny.cz>
> > Cc: stable at vger.kernel.org
> > Signed-off-by: Xi Ruoyao <xry111 at mengyan1223.wang>
> > ---
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> > b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> > index ad91c0c3c423..cee0cc9c8085 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> > @@ -1707,7 +1707,7 @@ static int amdgpu_vm_bo_update_mapping(struct
> > amdgpu_device *adev,
> >                 }
> >                 start = tmp;
> >   
> > -       } while (unlikely(start != last + 1));
> > +       } while (unlikely(start < last + 1));
> >   
> >         r = vm->update_funcs->commit(&params, fence);
> >   
> > 
> > base-commit: a5e13c6df0e41702d2b2c77c8ad41677ebb065b3
> 

-- 
Xi Ruoyao <xry111 at mengyan1223.wang>
School of Aerospace Science and Technology, Xidian University