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.
Regards,
Lucas
> offset += meta->nr_domains;
> continue;
> }
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