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Message-ID: <a7011738-a084-46fa-947f-395d90b37f8b@arm.com>
Date: Wed, 27 Nov 2024 15:24:32 +0000
From: Steven Price <steven.price@....com>
To: Marc Zyngier <maz@...nel.org>
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 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

Thanks,
Steve


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