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Date: Thu, 11 Apr 2024 08:23:23 +0900
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Subject: Re: [PATCH 0/3] tso: aarch64: Expose TSO for virtualized linux on
 Apple Silicon
To: Zayd Qumsieh <zayd_qumsieh@apple.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>,
 Mark Brown <broonie@kernel.org>, Ard Biesheuvel <ardb@kernel.org>,
 Mark Rutland <mark.rutland@arm.com>, Mateusz Guzik <mjguzik@gmail.com>,
 Anshuman Khandual <anshuman.khandual@arm.com>, Marc Zyngier
 <maz@kernel.org>, Oliver Upton <oliver.upton@linux.dev>,
 Miguel Luis <miguel.luis@oracle.com>, Joey Gouly <joey.gouly@arm.com>,
 Christoph Paasch <cpaasch@apple.com>, Kees Cook <keescook@chromium.org>,
 Sami Tolvanen <samitolvanen@google.com>, Baoquan He <bhe@redhat.com>,
 Lecopzer Chen <lecopzer.chen@mediatek.com>,
 Joel Granados <j.granados@samsung.com>, Dawei Li <dawei.li@shingroup.cn>,
 Andrew Morton <akpm@linux-foundation.org>,
 Florent Revest <revest@chromium.org>, David Hildenbrand <david@redhat.com>,
 Stefan Roesch <shr@devkernel.io>, Andy Chiu <andy.chiu@sifive.com>,
 Josh Triplett <josh@joshtriplett.org>, Oleg Nesterov <oleg@redhat.com>,
 Helge Deller <deller@gmx.de>, Zev Weiss <zev@bewilderbeest.net>,
 Ondrej Mosnacek <omosnace@redhat.com>, Miguel Ojeda <ojeda@kernel.org>,
 linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
 Justin Lu <ih_justin@apple.com>, Asahi Linux <asahi@lists.linux.dev>
References: <20240410211652.16640-1-zayd_qumsieh@apple.com>
From: Hector Martin <marcan@marcan.st>
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On 2024/04/11 6:16, Zayd Qumsieh wrote:
> x86 CPUs use a TSO memory model. Apple Silicon CPUs have the ability to
> selectively use a TSO memory model. This can be done by setting the
> ACTLR.TSOEN bit to 1. This feature is useful for x86 emulators, since it
> removes the need for emulators to insert memory barriers in order to abide
> by the TSO memory model. This patch series will add ACTLR.TSOEN support to
> virtualized linux on Apple Silicon machines. Userspace will be able to use
> a prctl to change the memory model of the CPU from the default ARM64 memory
> model to a TSO memory model.
> 
> A simple test can be used to determine if the TSO memory model is in use.
> This must be done on Apple Silicon MacOS Sonoma version 14.4 or later,
> since earlier versions do not support modification of the TSOEN bit.
> https://github.com/saagarjha/TSOEnabler/blob/master/testtso/main.c
> 
> This program will hang indefinitely if TSO is in use, and will crash almost
> immediately if it is not in use.

Well this is unexpected, given I talked to Justin Lu at Apple back in
December and I thought our plan was to work together on the series I've
had cooking in the Asahi tree [1] for a while now, which is actually
shipping in thousands of Asahi Linux systems in production and actually
already supported by the FEX-Emu project with our ABI. You CCed 30+
people, but not me nor the asahi@lists.linux.dev mailing list...

[1] https://github.com/AsahiLinux/linux/tree/bits/220-tso

Given that we're here now, I'll send out my series for review and see
what people think about that one.

> 
> Zayd Qumsieh (3):
>   tso: aarch64: allow linux kernel to read/write ACTLR.TSOEN
>   tso: aarch64: context-switch tso bit on thread switch
>   tso: aarch64: allow userspace to set tso bit using prctl
> 
>  arch/arm64/Kconfig                 | 19 +++++++++
>  arch/arm64/include/asm/processor.h |  4 ++
>  arch/arm64/include/asm/sysreg.h    |  7 ++++
>  arch/arm64/include/asm/tso.h       | 19 +++++++++
>  arch/arm64/kernel/Makefile         |  2 +-
>  arch/arm64/kernel/process.c        | 61 +++++++++++++++++++++++++++++
>  arch/arm64/kernel/tso.c            | 62 ++++++++++++++++++++++++++++++
>  include/uapi/linux/prctl.h         |  9 +++++
>  kernel/sys.c                       | 11 ++++++
>  9 files changed, 193 insertions(+), 1 deletion(-)
>  create mode 100644 arch/arm64/include/asm/tso.h
>  create mode 100644 arch/arm64/kernel/tso.c
> 

- Hector