linux-kernel - Re: [PATCH 0/4] arm64: Support the TSO memory model

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Date: Fri, 19 Apr 2024 17:58:26 +0100
From: Will Deacon <will@...nel.org>
To: Zayd Qumsieh <zayd_qumsieh@...le.com>
Cc: Hector Martin <marcan@...can.st>,
	Catalin Marinas <catalin.marinas@....com>,
	Marc Zyngier <maz@...nel.org>, Mark Rutland <mark.rutland@....com>,
	Justin Lu <ih_justin@...le.com>,
	Ryan Houdek <Houdek.Ryan@...-emu.org>,
	Mark Brown <broonie@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
	Mateusz Guzik <mjguzik@...il.com>,
	Anshuman Khandual <anshuman.khandual@....com>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Miguel Luis <miguel.luis@...cle.com>,
	Joey Gouly <joey.gouly@....com>,
	Christoph Paasch <cpaasch@...le.com>,
	Kees Cook <keescook@...omium.org>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Baoquan He <bhe@...hat.com>, Joel Granados <j.granados@...sung.com>,
	Dawei Li <dawei.li@...ngroup.cn>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Florent Revest <revest@...omium.org>,
	David Hildenbrand <david@...hat.com>,
	Stefan Roesch <shr@...kernel.io>, Andy Chiu <andy.chiu@...ive.com>,
	Josh Triplett <josh@...htriplett.org>,
	Oleg Nesterov <oleg@...hat.com>, Helge Deller <deller@....de>,
	Zev Weiss <zev@...ilderbeest.net>,
	Ondrej Mosnacek <omosnace@...hat.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Asahi Linux <asahi@...ts.linux.dev>
Subject: Re: [PATCH 0/4] arm64: Support the TSO memory model

On Mon, Apr 15, 2024 at 07:22:41PM -0700, Zayd Qumsieh wrote:
> >I'm probably going to make myself hugely unpopular here, but I have a
> >strong objection to this patch series as it stands. I firmly believe
> >that providing a prctl() to query and toggle the memory model to/from
> >TSO is going to lead to subtle fragmentation of arm64 Linux userspace.
> 
> It's definitely not our intent to fragment the ecosystem.
> The goal of this memory ordering is to simplify emulation layers that benefit from this.
> If you have suggestions to reduce the risk of it being misused outside of emulators, we'd be happy to look into it.

Once you have exposed this toggle via prctl(), it doesn't really matter
what your intentions where. It will get used outside of emulation laters
and we'll be stuck supporting it.

Will