linux-kernel - Re: [RFC PATCH 0/5] RISC-V: Add dynamic TSO support

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Message-ID: <20231127-process-dinginess-cea6dd652b99@wendy>
Date:   Mon, 27 Nov 2023 10:36:44 +0000
From:   Conor Dooley <conor.dooley@...rochip.com>
To:     Christoph Muellner <christoph.muellner@...ll.eu>
CC:     <linux-riscv@...ts.infradead.org>,
        <linux-kselftest@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Anup Patel <apatel@...tanamicro.com>,
        Philipp Tomsich <philipp.tomsich@...ll.eu>,
        Andrew Jones <ajones@...tanamicro.com>,
        Guo Ren <guoren@...nel.org>,
        Daniel Henrique Barboza <dbarboza@...tanamicro.com>,
        Björn Töpel <bjorn@...osinc.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Andrea Parri <parri.andrea@...il.com>,
        Will Deacon <will@...nel.org>,
        Daniel Lustig <dlustig@...dia.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC PATCH 0/5] RISC-V: Add dynamic TSO support

Hi,

On Fri, Nov 24, 2023 at 08:21:37AM +0100, Christoph Muellner wrote:
> From: Christoph Müllner <christoph.muellner@...ll.eu>
> 
> The upcoming RISC-V Ssdtso specification introduces a bit in the senvcfg
> CSR to switch the memory consistency model at run-time from RVWMO to TSO
> (and back). The active consistency model can therefore be switched on a
> per-hart base and managed by the kernel on a per-process/thread base.
> 
> This patch implements basic Ssdtso support and adds a prctl API on top
> so that user-space processes can switch to a stronger memory consistency
> model (than the kernel was written for) at run-time.
> 
> I am not sure if other architectures support switching the memory
> consistency model at run-time, but designing the prctl API in an
> arch-independent way allows reusing it in the future.
> 
> The patchset also comes with a short documentation of the prctl API.
> 
> This series is based on the second draft of the Ssdtso specification
> which was published recently on an RVI list:
>   https://lists.riscv.org/g/tech-arch-review/message/183
> Note, that the Ssdtso specification is in development state
> (i.e., not frozen or even ratified) which is also the reason
> why I marked the series as RFC.
> 
> One aspect that is not covered in this patchset is virtualization.
> It is planned to add virtualization support in a later version.
> Hints/suggestions on how to implement this part are very much
> appreciated.
> 
> Christoph Müllner (5):

I know this is an RFC, but it could probably do with a bit more compile
testing, as:

>   RISC-V: Add basic Ssdtso support

This patch doesn't build for rv64 allmodconfig

>   RISC-V: Expose Ssdtso via hwprobe API

This one seems to build fine

>   uapi: prctl: Add new prctl call to set/get the memory consistency
>     model
>   RISC-V: Implement prctl call to set/get the memory consistency model
>   RISC-V: selftests: Add DTSO tests

These don't build for:
rv32 defconfig
rv64 allmodconfig
rv64 nommu

Cheers,
Conor.

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