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

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Date:   Fri, 15 May 2020 12:12:33 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Christian Gmeiner <christian.gmeiner@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, stable@...r.kernel.org,
        Lucas Stach <l.stach@...gutronix.de>,
        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

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.

-Paul