linux-kernel - Re: [PATCH v4 7/9] riscv: vector: adjust minimum Vector requirement to ZVE32X

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Message-ID: <20240418-dolphin-epileptic-749c9628e5a9@spud>
Date: Thu, 18 Apr 2024 21:00:01 +0100
From: Conor Dooley <conor@...nel.org>
To: Eric Biggers <ebiggers@...nel.org>
Cc: Conor Dooley <conor.dooley@...rochip.com>,
	Andy Chiu <andy.chiu@...ive.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, Heiko Stuebner <heiko@...ech.de>,
	Guo Ren <guoren@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Jonathan Corbet <corbet@....net>, Evan Green <evan@...osinc.com>,
	Clément Léger <cleger@...osinc.com>,
	Shuah Khan <shuah@...nel.org>, linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org, Palmer Dabbelt <palmer@...osinc.com>,
	Vincent Chen <vincent.chen@...ive.com>,
	Greentime Hu <greentime.hu@...ive.com>, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
	Joel Granados <j.granados@...sung.com>,
	Jerry Shih <jerry.shih@...ive.com>
Subject: Re: [PATCH v4 7/9] riscv: vector: adjust minimum Vector requirement
 to ZVE32X

On Thu, Apr 18, 2024 at 11:41:29AM -0700, Eric Biggers wrote:

> If the RISC-V kernel ever disables V, then it should also disable everything
> that depends on V.
> 
> This would be similar to how on x86, if the kernel decides to disable AVX to
> mitigate the Gather Data Sampling vulnerability, it also disables AVX2, AVX512,
> VAES, VPCLMULQDQ, etc.  See cpuid_deps[] in arch/x86/kernel/cpu/cpuid-deps.c.
> 
> Sometimes CPU features depend on other ones.  That's just the way things work.

🤨

> Whenever possible that should be handled centrally, not pushed down to every
> user both in-kernel and userspace.

FWIW, anything detected but rejected while probing the DT or ACPI tables
will cause riscv_isa_extension_available() (or other APIs) to return false.


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