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

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Message-ID: <ZKsi+UOdjlmDnhdj@finisterre.sirena.org.uk>
Date:   Sun, 9 Jul 2023 22:13:29 +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 09, 2023 at 10:56:13AM -0400, Sasha Levin wrote:
> 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:

> > > 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.

That's saying that the code won't work properly on systems where some
but not all of the CPUs support the feature.  Note that the changelog
says nothing about fixing any issue here.

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