[PATCH] drm/etnaviv: fix perfmon domain interation

[Lucas Stach]

Am Freitag, den 15.05.2020, 12:27 +0200 schrieb Christian Gmeiner:
> Am Fr., 15. Mai 2020 um 12:24 Uhr schrieb Lucas Stach <l.stach at pengutronix.de>:
> > Am Freitag, den 15.05.2020, 12:12 +0200 schrieb Paul Cercueil:
> > > Hi Christian,
> > > 
> > > Le ven. 15 mai 2020 à 12:09, Christian Gmeiner
> > > <christian.gmeiner at gmail.com> a écrit :
> > > > Am Mo., 11. Mai 2020 um 14:38 Uhr schrieb Christian Gmeiner
> > > > <christian.gmeiner at gmail.com>:
> > > > >  The GC860 has one GPU device which has a 2d and 3d core. In this
> > > > > case
> > > > >  we want to expose perfmon information for both cores.
> > > > > 
> > > > >  The driver has one array which contains all possible perfmon domains
> > > > >  with some meta data - doms_meta. Here we can see that for the GC860
> > > > >  two elements of that array are relevant:
> > > > > 
> > > > >    doms_3d: is at index 0 in the doms_meta array with 8 perfmon
> > > > > domains
> > > > >    doms_2d: is at index 1 in the doms_meta array with 1 perfmon
> > > > > domain
> > > > > 
> > > > >  The userspace driver wants to get a list of all perfmon domains and
> > > > >  their perfmon signals. This is done by iterating over all domains
> > > > > and
> > > > >  their signals. If the userspace driver wants to access the domain
> > > > > with
> > > > >  id 8 the kernel driver fails and returns invalid data from doms_3d
> > > > > with
> > > > >  and invalid offset.
> > > > > 
> > > > >  This results in:
> > > > >    Unable to handle kernel paging request at virtual address 00000000
> > > > > 
> > > > >  On such a device it is not possible to use the userspace driver at
> > > > > all.
> > > > > 
> > > > >  The fix for this off-by-one error is quite simple.
> > > > > 
> > > > >  Reported-by: Paul Cercueil <paul at crapouillou.net>
> > > > >  Tested-by: Paul Cercueil <paul at crapouillou.net>
> > > > >  Fixes: ed1dd899baa3 ("drm/etnaviv: rework perfmon query
> > > > > infrastructure")
> > > > >  Cc: stable at vger.kernel.org
> > > > >  Signed-off-by: Christian Gmeiner <christian.gmeiner at gmail.com>
> > > > >  ---
> > > > >   drivers/gpu/drm/etnaviv/etnaviv_perfmon.c | 2 +-
> > > > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > 
> > > > >  diff --git a/drivers/gpu/drm/etnaviv/etnaviv_perfmon.c
> > > > > b/drivers/gpu/drm/etnaviv/etnaviv_perfmon.c
> > > > >  index e6795bafcbb9..35f7171e779a 100644
> > > > >  --- a/drivers/gpu/drm/etnaviv/etnaviv_perfmon.c
> > > > >  +++ b/drivers/gpu/drm/etnaviv/etnaviv_perfmon.c
> > > > >  @@ -453,7 +453,7 @@ static const struct etnaviv_pm_domain
> > > > > *pm_domain(const struct etnaviv_gpu *gpu,
> > > > >                  if (!(gpu->identity.features & meta->feature))
> > > > >                          continue;
> > > > > 
> > > > >  -               if (meta->nr_domains < (index - offset)) {
> > > > >  +               if ((meta->nr_domains - 1) < (index - offset)) {
> > > > >                          offset += meta->nr_domains;
> > > > >                          continue;
> > > > >                  }
> > > > >  --
> > > > >  2.26.2
> > > > > 
> > > > 
> > > > ping
> > > 
> > > I'll merge it tomorrow if there's no further feedback.
> > 
> > Huh? Etnaviv patches are going through the etnaviv tree.
> > 
> > We now have two different solutions to the same issue. I first want to
> > dig into the code to see why two developers can get confused enough by
> > the code to come up with totally different fixes.
> > 
> 
> You will see that the solutions are not totally different. I really hoped to
> get this fixed in the 5.7 release.. but I think its now too late.

I didn't have time to look at the full picture, yet. We still have at
least a week until the final 5.7 release, why would it be too late to
get a fix upstream?

Regards,
Lucas