From: Marc Zyngier <maz@kernel.org>
To: Mark Brown <broonie@kernel.org>
Cc: Oliver Upton <oupton@kernel.org>,
Fuad Tabba <fuad.tabba@linux.dev>,
Joey Gouly <joey.gouly@arm.com>,
Steffen Eiden <seiden@linux.ibm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Zenghui Yu <yuzenghui@huawei.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] KVM: arm64: Initialise TCR2_EL2 for nVHE mode
Date: Fri, 04 Sep 2026 14:13:10 +0100 [thread overview]
Message-ID: <87zexx40t5.wl-maz@kernel.org> (raw)
In-Reply-To: <d9c3a882-fcf7-4cd3-93df-b0218961e145@sirena.org.uk>
On Fri, 04 Sep 2026 12:35:22 +0100,
Mark Brown <broonie@kernel.org> wrote:
>
> On Fri, Sep 04, 2026 at 08:32:04AM +0100, Marc Zyngier wrote:
> > Mark Brown <broonie@kernel.org> wrote:
>
> > > +alternative_if ARM64_HAS_TCR2
> > > + /*
> > > + * Disable any features we enabled in case the next user doesn't
> > > + * have TCR2_EL2 support.
> > > + */
> > > + msr REG_TCR2_EL2, xzr
> > > +alternative_else_nop_endif
>
> > I don't see the point of this. The MMU is off, and if the next piece
> > of SW can't correctly initialise the HW, that's its problem.
>
> So we don't care about reverting back to users who are just plain
> unaware of the register? In practice for Linux that's fairly old
> kernels, but people might feel adverturous and try or try some non-Linux
> thing. This stuff is all a bit edge casey with what we support.
I certainly do not care. If you kexec an ancient kernel on new HW and
can't correctly initialise it, you lose. Don't do that.
M.
--
Jazz isn't dead. It just smells funny.
next prev parent reply other threads:[~2026-09-04 13:58 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-03 23:14 [PATCH 0/2] KVM: arm64: Enable S1PIE for nVHE and hVHE Mark Brown
2026-09-03 23:14 ` [PATCH 1/2] KVM: arm64: Initialise TCR2_EL2 for nVHE mode Mark Brown
2026-09-04 7:32 ` Marc Zyngier
2026-09-04 11:35 ` Mark Brown
2026-09-04 13:13 ` Marc Zyngier [this message]
2026-09-03 23:14 ` [PATCH 2/2] KVM: arm64: Enable S1PIE for nVHE and hVHE Mark Brown
2026-09-04 7:25 ` Marc Zyngier
2026-09-04 10:33 ` Mark Brown
2026-09-04 11:29 ` Will Deacon
2026-09-04 11:48 ` Mark Brown
2026-09-04 12:20 ` Fuad Tabba
2026-09-04 13:38 ` Mark Brown
2026-09-04 13:57 ` Marc Zyngier
2026-09-04 17:40 ` Mark Brown
2026-09-04 13:41 ` Will Deacon
2026-09-04 14:13 ` Alexandru Elisei
2026-09-04 13:23 ` Marc Zyngier
2026-09-04 13:53 ` Mark Brown
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