VCN_INFO_TABLE_MAX_NUM_INSTANCES vs AMDGPU_MAX_VCN_INSTANCES

[Alex Deucher]

On Mon, May 16, 2022 at 2:10 PM Christian König
<ckoenig.leichtzumerken at gmail.com> wrote:
>
> Am 16.05.22 um 19:49 schrieb Ernst Sjöstrand:
>
> Den mån 16 maj 2022 kl 17:13 skrev Alex Deucher <alexdeucher at gmail.com>:
>>
>> On Sun, May 15, 2022 at 11:46 AM Ernst Sjöstrand <ernstp at gmail.com> wrote:
>> >
>> > smatch found this problem on amd-staging-drm-next:
>> >
>> > drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:1443 amdgpu_discovery_get_vcn_info() error: buffer overflow 'adev->vcn.vcn_codec_disable_mask' 2 <= 3
>> >
>> > This is caused by:
>> > #define AMDGPU_MAX_VCN_INSTANCES 2
>> > #define VCN_INFO_TABLE_MAX_NUM_INSTANCES 4
>> >
>> > Can we just drop VCN_INFO_TABLE_MAX_NUM_INSTANCES completely and use AMDGPU_MAX_VCN_INSTANCES everywhere instead (and bump it to 4)?
>>
>> We should be able to bump AMDGPU_MAX_VCN_INSTANCES to 4 (although it
>> would waste some memory in the places it is used at this point).
>> VCN_INFO_TABLE_MAX_NUM_INSTANCES is part of a firmware structure so we
>> can't change that without breaking the firmware structure.
>>
>> Alex
>
>
> It would be nice to get rid of this pattern and make sure it doesn't happen again when the VCN info table is raised to 5.
> It's very similar to the HWIP_MAX_INSTANCE issue.
>
>
> No, as Alex explained that distinction is intentional.
>
> The firmware definition is 4 for future extensions, that doesn't mean that this is currently used.
>
> There is currently simply no need to set AMDGPU_MAX_VCN_INSTANCES to more than 2.

Right.  The attached patch should protect against the scenario you are
envisioning.

Alex

>
> Regards,
> Christian.
>
>
> //E
>
>
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