linux-kernel - Re: [PATCH] drm/etnaviv: fix perfmon domain interation

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Date:   Fri, 15 May 2020 12:24:47 +0200
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Paul Cercueil <paul@...pouillou.net>,
        Christian Gmeiner <christian.gmeiner@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, stable@...r.kernel.org,
        Russell King <linux+etnaviv@...linux.org.uk>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        The etnaviv authors <etnaviv@...ts.freedesktop.org>,
        DRI mailing list <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH] drm/etnaviv: fix perfmon domain interation

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@...il.com> a écrit :
> > Am Mo., 11. Mai 2020 um 14:38 Uhr schrieb Christian Gmeiner
> > <christian.gmeiner@...il.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@...pouillou.net>
> > >  Tested-by: Paul Cercueil <paul@...pouillou.net>
> > >  Fixes: ed1dd899baa3 ("drm/etnaviv: rework perfmon query 
> > > infrastructure")
> > >  Cc: stable@...r.kernel.org
> > >  Signed-off-by: Christian Gmeiner <christian.gmeiner@...il.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.

Regards,
Lucas