Re: [PATCH v3 4/6] riscv: hwprobe: export Zawrs ISA extension

From: Conor Dooley <conor@kernel.org>
To: Andrew Jones <ajones@ventanamicro.com>
Cc: "Clément Léger" <cleger@rivosinc.com>,
	linux-riscv@lists.infradead.org, kvm-riscv@lists.infradead.org,
	devicetree@vger.kernel.org, paul.walmsley@sifive.com,
	palmer@dabbelt.com, aou@eecs.berkeley.edu,
	conor.dooley@microchip.com, anup@brainfault.org,
	atishp@atishpatra.org, robh@kernel.org,
	krzysztof.kozlowski+dt@linaro.org, conor+dt@kernel.org,
	christoph.muellner@vrull.eu, heiko@sntech.de,
	charlie@rivosinc.com, David.Laight@aculab.com,
	parri.andrea@gmail.com, luxu.kernel@bytedance.com
Subject: Re: [PATCH v3 4/6] riscv: hwprobe: export Zawrs ISA extension
Date: Tue, 18 Jun 2024 18:34:50 +0100	[thread overview]
Message-ID: <20240618-hurler-aerospace-1e42dc3c7fe9@spud> (raw)
In-Reply-To: <20240618-e898082d22cbc508c5655f84@orel>


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On Tue, Jun 18, 2024 at 07:05:41PM +0200, Andrew Jones wrote:
> On Tue, Jun 18, 2024 at 05:59:22PM GMT, Conor Dooley wrote:
> > On Tue, Jun 18, 2024 at 06:01:04PM +0200, Andrew Jones wrote:
> > > On Tue, Jun 18, 2024 at 03:48:59PM GMT, Clément Léger wrote:
> > > > On 26/04/2024 12:08, Andrew Jones wrote:

> > > > 
> > > > BTW, the spec also states that "When the TW (Timeout Wait) bit in
> > > > mstatus is set and WRS.NTO is executed in any privilege mode other than
> > > > M mode, and it does not complete within an implementation-specific
> > > > bounded time limit, the WRS.NTO instruction will cause an illegal
> > > > instruction exception." so I guess the process will be killed in this case ?
> > > 
> > > We don't expect mstatus.TW to be set. If it is, then wfi would likely kill
> > > the kernel before wrs.nto gets a chance to, but one or the other will
> > > certainly ensure usermode never gets a chance to try it :-)
> > > 
> > > We have a handful of these assumptions about how M-mode has configured
> > > things prior to Linux starting. It'd be good if we documented them all
> > > somewhere.
> > 
> > Boot.rst :) If you're adding a new assumption, I think it should go
> > there.
> 
> It's an old assumption (wfi has been counting on it since the beginning of
> time). But documenting it, along with anything else similar to it, in
> boot.rst is a good idea. I've added that to my TODO.

Misunderstanding of "new" I think, I meant new to documentation not just
new to the kernel :)

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