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

From: Conor Dooley <conor@kernel.org>
To: Eric Biggers <ebiggers@kernel.org>
Cc: "Conor Dooley" <conor.dooley@microchip.com>,
	"Andy Chiu" <andy.chiu@sifive.com>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	"Heiko Stuebner" <heiko@sntech.de>, "Guo Ren" <guoren@kernel.org>,
	"Rob Herring" <robh@kernel.org>,
	"Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Evan Green" <evan@rivosinc.com>,
	"Clément Léger" <cleger@rivosinc.com>,
	"Shuah Khan" <shuah@kernel.org>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	"Palmer Dabbelt" <palmer@rivosinc.com>,
	"Vincent Chen" <vincent.chen@sifive.com>,
	"Greentime Hu" <greentime.hu@sifive.com>,
	devicetree@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-kselftest@vger.kernel.org,
	"Joel Granados" <j.granados@samsung.com>,
	"Jerry Shih" <jerry.shih@sifive.com>
Subject: Re: [PATCH v4 7/9] riscv: vector: adjust minimum Vector requirement to ZVE32X
Date: Thu, 18 Apr 2024 21:00:01 +0100	[thread overview]
Message-ID: <20240418-dolphin-epileptic-749c9628e5a9@spud> (raw)
In-Reply-To: <20240418184129.GA1071@sol.localdomain>

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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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