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Date: Wed, 7 Feb 2024 15:07:38 +0000
From: Mark Brown <broonie@kernel.org>
To: Dave Martin <Dave.Martin@arm.com>
Cc: Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Oleg Nesterov <oleg@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
	linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
	Doug Anderson <dianders@chromium.org>
Subject: Re: [PATCH] arm64/sve: Lower the maximum allocation for the SVE
 ptrace regset
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References: <20240203-arm64-sve-ptrace-regset-size-v1-1-2c3ba1386b9e@kernel.org>
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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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