linux-kernel - Re: [PATCH] KVM: arm64: Bump KVM_VCPU_MAX

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Message-ID: <868qt4vg3e.wl-maz@kernel.org>
Date: Wed, 27 Nov 2024 15:41:57 +0000
From: Marc Zyngier <maz@...nel.org>
To: Steven Price <steven.price@....com>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Will Deacon <will@...nel.org>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	kvmarm@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: arm64: Bump KVM_VCPU_MAX_FEATURES

On Wed, 27 Nov 2024 15:24:32 +0000,
Steven Price <steven.price@....com> wrote:
> 
> On 27/11/2024 15:16, Marc Zyngier wrote:
> > On Wed, 27 Nov 2024 14:56:31 +0000,
> > Steven Price <steven.price@....com> wrote:
> >>
> >> When the KVM_ARM_VCPU_HAS_EL2 define was added, the value of
> >> KVM_VCPU_MAX_FEATURES wasn't incremented, so that feature has never been
> >> in the KVM_VCPU_VALID_FEATURES bit mask. This means the HAS_EL2 feature
> >> will never be exposed to user space even if the system supports it.
> >>
> >> Fixes: 89b0e7de3451 ("KVM: arm64: nv: Introduce nested virtualization VCPU feature")
> >> Signed-off-by: Steven Price <steven.price@....com>
> >> ---
> >> I might be missing something, and it's possible that
> >> KVM_ARM_VCPU_HAS_EL2 is deliberately not exposed yet.
> > 
> > This is on purpose. I'm not planning to enable EL2 support until it is
> > ready.
> 
> I did suspect that's the case - but it might have been better to knobble
> it in system_supported_vcpu_features()/kvm_vcpu_init_check_features()
> rather than 'hiding' it in the MAX_FEATURES. But hindsight is a
> wonderful thing ;)
> 
> >> However I'm
> >> working on v6 of the host CCA series and as part of that want to add a
> >> new feature but and bump KVM_VCPU_MAX_FEATURES up to 9.
> > 
> > Well, I guess that defines some ordering then! :D
> 
> Indeed - I'll try to remember to include note about this "dependency" in
> my cover letter. We're likely to need a few more rounds for CCA to be
> ready, so hopefully NV will naturally be there in time :D

Any minute now, according to those impersonating a French physicist...

	M.

-- 
Without deviation from the norm, progress is not possible.