linux-kernel - Re: [PATCH v5 03/22] KVM: arm64: Support SDEI

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Date:   Tue, 22 Mar 2022 18:04:52 +0000
From:   Oliver Upton <oupton@...gle.com>
To:     Gavin Shan <gshan@...hat.com>
Cc:     kvmarm@...ts.cs.columbia.edu, maz@...nel.org,
        linux-kernel@...r.kernel.org, eauger@...hat.com,
        shan.gavin@...il.com, Jonathan.Cameron@...wei.com,
        pbonzini@...hat.com, vkuznets@...hat.com, will@...nel.org
Subject: Re: [PATCH v5 03/22] KVM: arm64: Support SDEI_VERSION hypercall

On Tue, Mar 22, 2022 at 04:06:51PM +0800, Gavin Shan wrote:
> This supports SDEI_VERSION hypercall by returning v1.1, which is
> the specification version we're following. The vendor is set to
> 'KVM'.
> 
> Signed-off-by: Gavin Shan <gshan@...hat.com>
> ---
>  arch/arm64/kvm/sdei.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/arch/arm64/kvm/sdei.c b/arch/arm64/kvm/sdei.c
> index 8a9b477b8977..5a3a64cd6e84 100644
> --- a/arch/arm64/kvm/sdei.c
> +++ b/arch/arm64/kvm/sdei.c
> @@ -118,6 +118,14 @@ static bool remove_all_vcpu_events(struct kvm_vcpu *vcpu,
>  	return pending;
>  }
>  
> +static unsigned long hypercall_version(struct kvm_vcpu *vcpu)
> +{
> +	/* v1.1 and the vendor is KVM */
> +	return (1UL << SDEI_VERSION_MAJOR_SHIFT) |
> +	       (1UL << SDEI_VERSION_MINOR_SHIFT) |
> +	       0x4b564d;

It looks like the SDEI specification states that the vendor-defined
version number is 32 bits. Could we just use one of the
ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_{0,3} values instead?

ASCII 'KVM' is neat, but in reality guest software will just throw it in
a macro regardless. Might as well use one of the values we've already
trained it to use :-)

Also, it would appear that guest discovery of SDEI relies upon KVM
reporting a valid SDEI version. IMO, this patch should come at the very
end when KVM actually implements SDEI.

--
Thanks,
Oliver