[PATCH rc] iommu/arm-smmu-v3: Do not use GFP_KERNEL under as spinlock

[Jason Gunthorpe]

On Tue, Feb 13, 2024 at 12:54:56PM +0000, Will Deacon wrote:
> > Adding a check is not a comprehensive solution, there are still ways
> > userspace can attack this code with iommufd's coming PASID support. It
> > certainly doesn't belong in this patch which should be backported.
> 
> Ok, then how about avoiding the allocation entirely once the lock is
> held?

We need to allocate because we can't assume anything already made the
CD leaf present. Do you mean to do this additionally to this patch?

There are several places where a noalloc CD behavior would be useful,
I'd be fine to add that as part of this patch to protect the loop.

> > I can summarize some of these details in a comment for this patch.
>
> Alternatively, we can just revert the offending commits if we're not able
> to agree on a simple fix for now. I'd prefer to avoid that though.

I feel we are not aligned here. We are trying to get the driver to
work properly with iommufd and expose all the HW features. This has
been fixed comprehensively and well-reviewed patches have been on the
list for 7 months now. We want to move forward, not revert things.

Jason