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

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Message-ID: <ZKrKjS7sDFxhKoJT@sashalap>
Date:   Sun, 9 Jul 2023 10:56:13 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     Mark Brown <broonie@...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 Mon, Jul 03, 2023 at 12:51:57PM +0100, Mark Brown wrote:
>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)?

The second paragraph (above) suggested it should be.

-- 
Thanks,
Sasha