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* Re: [PATCH v2] hw/arm/virt: KVM: Enable PAuth when supported by the host
From: Richard Henderson @ 2022-01-05 21:36 UTC (permalink / raw)
  To: Marc Zyngier, qemu-devel
  Cc: kvmarm, kvm, kernel-team, Eric Auger, Andrew Jones, Peter Maydell
In-Reply-To: <20220103180507.2190429-1-maz@kernel.org>

On 1/3/22 10:05 AM, Marc Zyngier wrote:
> -        /*
> -         * KVM does not support modifications to this feature.
> -         * We have not registered the cpu properties when KVM
> -         * is in use, so the user will not be able to set them.
> -         */
> -        if (!kvm_enabled()) {
> -            arm_cpu_pauth_finalize(cpu, &local_err);
> -            if (local_err != NULL) {
> +	arm_cpu_pauth_finalize(cpu, &local_err);
> +	if (local_err != NULL) {
>                   error_propagate(errp, local_err);
>                   return;
> -            }
> -        }
> +	}

Looks like the indentation is off?

> +static bool kvm_arm_pauth_supported(void)
> +{
> +    return (kvm_check_extension(kvm_state, KVM_CAP_ARM_PTRAUTH_ADDRESS) &&
> +            kvm_check_extension(kvm_state, KVM_CAP_ARM_PTRAUTH_GENERIC));
> +}

Do we really need to have them both set to play the game?  Given that the only thing that 
happens is that we disable whatever host support exists, can we have "pauth enabled" mean 
whatever subset the host has?

> @@ -521,6 +527,17 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
>        */
>       struct kvm_vcpu_init init = { .target = -1, };
>   
> +    /*
> +     * Ask for Pointer Authentication if supported. We can't play the
> +     * SVE trick of synthetising the ID reg as KVM won't tell us

synthesizing

> +     * whether we have the architected or IMPDEF version of PAuth, so
> +     * we have to use the actual ID regs.
> +     */
> +    if (kvm_arm_pauth_supported()) {
> +        init.features[0] |= (1 << KVM_ARM_VCPU_PTRAUTH_ADDRESS |
> +			     1 << KVM_ARM_VCPU_PTRAUTH_GENERIC);

Align the two 1's.

Otherwise, it looks good.

r~

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