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

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Message-ID: <ZcOcumjBZSYvWya1@finisterre.sirena.org.uk>
Date: Wed, 7 Feb 2024 15:07:38 +0000
From: Mark Brown <broonie@...nel.org>
To: Dave Martin <Dave.Martin@....com>
Cc: Will Deacon <will@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Oleg Nesterov <oleg@...hat.com>, Al Viro <viro@...iv.linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Doug Anderson <dianders@...omium.org>
Subject: 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:

> > 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.

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