Re: [PATCH] arm64/sve: Lower the maximum allocation for the SVE ptrace regset

On Wed, Feb 07, 2024 at 01:51:42PM +0000, Dave Martin wrote:

On Wed, Feb 07, 2024 at 01:09:51PM +0000, Mark Brown wrote:

quoted

I think if we fix the ptrace regset issue we're doing a good enough job
of just using fully dynamic sizing with no limits other than what's been
enumerated there.  We could possibly deal with the enumberation code by
changing it to use ZCR/SMCR_ELx_LEN_ based defines so that it's
obviously coming from what we can possibly write to the register but
it's a bit less clear how to do that neatly.

OK, but we still seem to have two competing approaches: clamp SVE_VQ_MAX
for kernel internal purposes, or restore the dynamic sizing of
NT_ARM_SVE based on the new regset core behaviour.

Are you saying we should or both, or otherwise which one?

I'd like to remove uses of SVE_VQ_MAX, to the extent possible by making
things dynamic but if not by not using it I would like to not use
SVE_VQ_MAX partly due to the considerations you mentioned about people
picking up from looking at the kernel source that it's a good idea.