linux-kernel - Re: [PATCH] regset: use vmalloc() for regset_get

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Date: Fri, 2 Feb 2024 11:13:08 -0800
From: Doug Anderson <dianders@...omium.org>
To: Dave Martin <Dave.Martin@....com>
Cc: Al Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, 
	Eric Biederman <ebiederm@...ssion.com>, Jan Kara <jack@...e.cz>, Kees Cook <keescook@...omium.org>, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, Oleg Nesterov <oleg@...hat.com>, 
	Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
	Mark Brown <broonie@...nel.org>, Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] regset: use vmalloc() for regset_get_alloc()

Hi,

On Fri, Feb 2, 2024 at 10:08 AM Dave Martin <Dave.Martin@....com> wrote:
>
> So, if the only reason for trying to migrate to vmalloc() is to cope
> with an insanely sized regset on arm64, I think somehow or other we can
> avoid that.

Right. The only reason for the patch to switch to vmalloc() was in
reaction to seeing the order 7 memory allocation. If we can decrease
that to something sensible then I'm happy enough keeping the
allocation as kmalloc().

> Options:
>
>  a) bring back ->get_size() so that we can allocate the correct size
> before generating the regset data;
>
>  b) make aarch64_regsets[] __ro_after_init and set
> aarch64_regsets[REGSET_SVE].n based on the boot-time probed maximum size
> (which will be sane); or
>
>  c) allow membufs to grow if needed (sounds fragile though, and may be
> hard to justify just for one arch?).
>
>
> Thoughts?
>
> If people don't want to bring back get_size(), then (b) doesn't look
> too bad.

Either a) or b) sounds fine to me, but I'm just a visitor to this code
so maybe I'll let the adults in the room chime in with their opinions.
;-) Also: if you think it's fruitful for me to try to write a patch to
do either of those then I can, but I also wouldn't object at all to
someone else writing a patch to fix this and I can just provide a
Tested-by and/or Reviewed-by. Let me know.

-Doug