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

From: Conor Dooley <conor.dooley@microchip.com>
To: Christoph Muellner <christoph.muellner@vrull.eu>
Cc: linux-riscv@lists.infradead.org, linux-kselftest@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Shuah Khan" <shuah@kernel.org>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Anup Patel" <apatel@ventanamicro.com>,
	"Philipp Tomsich" <philipp.tomsich@vrull.eu>,
	"Andrew Jones" <ajones@ventanamicro.com>,
	"Guo Ren" <guoren@kernel.org>,
	"Daniel Henrique Barboza" <dbarboza@ventanamicro.com>,
	"Björn Töpel" <bjorn@rivosinc.com>,
	"Alan Stern" <stern@rowland.harvard.edu>,
	"Andrea Parri" <parri.andrea@gmail.com>,
	"Will Deacon" <will@kernel.org>,
	"Daniel Lustig" <dlustig@nvidia.com>,
	"Peter Zijlstra" <peterz@infradead.org>
Subject: Re: [RFC PATCH 0/5] RISC-V: Add dynamic TSO support
Date: Mon, 27 Nov 2023 10:36:44 +0000	[thread overview]
Message-ID: <20231127-process-dinginess-cea6dd652b99@wendy> (raw)
In-Reply-To: <20231124072142.2786653-1-christoph.muellner@vrull.eu>

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Hi,

On Fri, Nov 24, 2023 at 08:21:37AM +0100, Christoph Muellner wrote:
> From: Christoph Müllner <christoph.muellner@vrull.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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