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From: Doug Anderson <dianders@chromium.org>
Date: Fri, 2 Feb 2024 11:13:08 -0800
Message-ID: <CAD=FV=XDg2Q2Gkv0pnngfUMJUOctXhe7f_33DW4TpLxTdG7KBw@mail.gmail.com>
Subject: Re: [PATCH] regset: use vmalloc() for regset_get_alloc()
To: Dave Martin <Dave.Martin@arm.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>, Christian Brauner <brauner@kernel.org>, 
	Eric Biederman <ebiederm@xmission.com>, Jan Kara <jack@suse.cz>, Kees Cook <keescook@chromium.org>, 
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, 
	linux-mm@kvack.org, Oleg Nesterov <oleg@redhat.com>, 
	Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>, 
	Mark Brown <broonie@kernel.org>, Linux ARM <linux-arm-kernel@lists.infradead.org>
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Hi,

On Fri, Feb 2, 2024 at 10:08=E2=80=AFAM Dave Martin <Dave.Martin@arm.com> w=
rote:
>
> 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