Re: Bad rss-counter state from drm/ttm, drm/vmwgfx: Support huge TTM pagefaults

[Thomas HellstrÃm (VMware)]

On 4/7/20 5:36 PM, Alex Xu (Hello71) wrote:
> Excerpts from Thomas HellstrÃm (VMware)'s message of April 7, 2020 7:26 am:
> > On 4/7/20 2:38 AM, Alex Xu (Hello71) wrote:
> > > Excerpts from Thomas HellstrÃm (VMware)'s message of April 6, 2020 5:04 pm:
> > > > Hi,
> > > >
> > > > On 4/6/20 9:51 PM, Alex Xu (Hello71) wrote:
> > > > > Using 314b658 with amdgpu, starting sway and firefox causes "BUG: Bad
> > > > > rss-counter state" and "BUG: non-zero pgtables_bytes on freeing mm" to
> > > > > start filling dmesg, and then closing programs causes more BUGs and
> > > > > hangs, and then everything grinds to a halt (can't start more programs,
> > > > > can't even reboot through systemd).
> > > > >
> > > > > Using master and reverting that branch up to that point fixes the
> > > > > problem.
> > > > >
> > > > > I'm using a Ryzen 1600 and AMD Radeon RX 480 on an ASRock B450 Pro4
> > > > > board with IOMMU enabled.
> > > > If you could try the attached patch, that'd be great!
> > > >
> > > > Thanks,
> > > >
> > > > Thomas
> > > Yeah, that works too. Kernel config sent off-list.
> > >
> > > Regards,
> > > Alex.
> > Thanks. Do you want me to add your
> >
> > Reported-by: and Tested-by: To this patch?
> >
> > /Thomas
> Sure. Shouldn't we fix it properly though?

It's still enabled for vmwgfx for which it is reasonably well tested and 
where I can't see any such errors.

The code we remove with this patch enables huge page-table entries in 
some circumstances for other drivers, but given the problems you're 
seeing for amdgpu, it's better to enable this on a per-driver basis 
after thorough testing. Since I don't have amdgpu hardware I'm not sure 
what it's doing differently, and can't debug the issue properly.

/Thomas