Re: [PATCH v4 4/4] gpu: nova-core: fix stack overflow in GSP memory allocation

["Danilo Krummrich" <dakr@kernel.org>]

On Tue Mar 10, 2026 at 3:28 AM CET, Alexandre Courbot wrote:
> On Tue Mar 10, 2026 at 10:51 AM JST, Gary Guo wrote:
>> On Tue Mar 10, 2026 at 1:40 AM GMT, Alexandre Courbot wrote:
>>> On Tue Mar 10, 2026 at 1:34 AM JST, Tim Kovalenko via B4 Relay wrote:
>>>> diff --git a/drivers/gpu/nova-core/gsp/cmdq.rs b/drivers/gpu/nova-core/gsp/cmdq.rs
>>>> index 0056bfbf0a44cfbc5a0ca08d069f881b877e1edc..c8327d3098f73f9b880eee99038ad10a16e1e32d 100644
>>>> --- a/drivers/gpu/nova-core/gsp/cmdq.rs
>>>> +++ b/drivers/gpu/nova-core/gsp/cmdq.rs
>>>> @@ -202,7 +202,20 @@ fn new(dev: &device::Device<device::Bound>) -> Result<Self> {
>>>>  
>>>>          let gsp_mem =
>>>>              CoherentAllocation::<GspMem>::alloc_coherent(dev, 1, GFP_KERNEL | __GFP_ZERO)?;
>>>> -        dma_write!(gsp_mem, [0]?.ptes, PteArray::new(gsp_mem.dma_handle())?);
>>>> +
>>>> +        const NUM_PTES: usize = GSP_PAGE_SIZE / size_of::<u64>();
>>>> +
>>>> +        let start = gsp_mem.dma_handle();
>>>> +        // One by one GSP Page write to the memory to avoid stack overflow when allocating
>>>> +        // the whole array at once.
>>>> +        for i in 0..NUM_PTES {
>>>> +            dma_write!(
>>>> +                gsp_mem,
>>>> +                [0]?.ptes.0[i],
>>>> +                PteArray::<NUM_PTES>::entry(start, i)?
>>>
>>> Does `::<NUM_PTES>` need to be mentioned here, or is the compiler able
>>> to infer it?
>>
>> The function signature doesn't mention NUM_PTES at all, so no. In fact, perhaps
>> the `entry` shouldn't be an associated method at all (even if is, it probably
>> should be of `PteArray::<0>` or something.

I think <0> is probably the best choice for this fix for now.

> I had that thought as well - this calls for a redesign of the `PteArray`
> business - but also didn't want to interfere too much as this fix is
> very much (and quickly) needed. We will probably re-write this once we
> have access to the new I/O code anyway.

Not sure it actually needs a redesign, as I think this just goes away with I/O
projections. That's also why I would add the following TODO comment on entry().

	// TODO: Replace with `IoView` projections once available.

I.e. it is just a workaround for now.