Re: [PATCH] gpu: nova-core: gsp: fix UB in DmaGspMem pointer accessors

[Danilo Krummrich]

On Tue Mar 10, 2026 at 4:56 AM CET, Eliot Courtney wrote:
> On Tue Mar 10, 2026 at 11:01 AM JST, Gary Guo wrote:
>>> +    pub(in crate::gsp) fn advance_cpu_write_ptr(qs: &CoherentAllocation<GspMem>, count: u32) {
>>> +        let wptr = cpu_write_ptr(qs).wrapping_add(count) & MSGQ_NUM_PAGES;
>>
>> Not really related to your change, but this `&` probably require a comment, as
>> it has different behaviour compared to `%` given the `MSGQ_NUM_PAGES` is not
>> power of two. I suppose this is actually intended so there's a way to
>> distinguish between empty and full ring buffer?
>
> This is actually incorrect and I have fixed it here[1]. I think it
> should be merged in drm-rust-next now.

Probably should have been going through -fixes. Anyways, I will fix it up in
this patch too.

> [1]: https://lore.kernel.org/all/20260129-nova-core-cmdq1-v3-0-2ede85493a27@xxxxxxxxxx/