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

[Christian Gmeiner]

Hi Lucas,

Am So., 17. Mai 2020 um 14:03 Uhr schrieb Lucas Stach <l.stach@xxxxxxxxxxxxxx>:
>
> Hi Christian,
>
> Am Montag, den 11.05.2020, 14:37 +0200 schrieb Christian Gmeiner:
> > 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@xxxxxxxxxxxxxxx>
> > Tested-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> > Fixes: ed1dd899baa3 ("drm/etnaviv: rework perfmon query infrastructure")
> > Cc: stable@xxxxxxxxxxxxxx
>
> Missing last letter of the TLD.
>
> > Signed-off-by: Christian Gmeiner <christian.gmeiner@xxxxxxxxx>
> > ---
> >  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)) {
>
> While the logic is correct, I find this quite hard to read. A more
> idiomatic way to write this (which is much easier to grok when reading
> the code IMHO) would be:
>
> if (index - offset >= meta->nr_domains)
>
> If you agree, please send a v2 of this patch.
>

Works for me - will send a v2 in the evening.

-- 
greets
--
Christian Gmeiner, MSc

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