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

[Christian König]

Am 29.03.21 um 20:08 schrieb 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.

You need to identify the root cause of this, most likely start or last 
are not a multiple of AMDGPU_GPU_PAGES_IN_CPU_PAGE.

Christian.

> > 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@xxxxxxxxxxxxxxxx>
> > > Reported-by: Dan Horák <dan@xxxxxxxx>
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > Signed-off-by: Xi Ruoyao <xry111@xxxxxxxxxxxxxxxx>
> > > ---
> > >    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