linux-kernel - Re: [PATCH AUTOSEL 6.4 07/12] arm64: cpufeature: detect FEAT

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Message-ID: <b37a9f79-97a8-4f74-a25c-b51128fbc9bb@sirena.org.uk>
Date:   Mon, 3 Jul 2023 12:51:57 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Kristina Martsenko <kristina.martsenko@....com>,
        Catalin Marinas <catalin.marinas@....com>, will@...nel.org,
        james.morse@....com, mark.rutland@....com, amit.kachhap@....com,
        maz@...nel.org, anshuman.khandual@....com, joey.gouly@....com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH AUTOSEL 6.4 07/12] arm64: cpufeature: detect FEAT_HCX

On Sun, Jul 02, 2023 at 03:50:52PM -0400, Sasha Levin wrote:
> From: Kristina Martsenko <kristina.martsenko@....com>
> 
> [ Upstream commit b0c756fe996ac930033882ca56410639e5cad1ec ]
> 
> Detect if the system has the new HCRX_EL2 register added in ARMv8.7/9.2,
> so that subsequent patches can check for its presence.
> 
> KVM currently relies on the register being present on all CPUs (or
> none), so the kernel will panic if that is not the case. Fortunately no
> such systems currently exist, but this can be revisited if they appear.
> Note that the kernel will not panic if CONFIG_KVM is disabled.

This is a new feature, it's not clear why we'd backport it (especially
since it's a new feature which is a dependency for other features rather
than something that people can use outside of the kernel)?

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