Subject: Re: [PATCH v4 03/14] KVM: arm64: Kill 32-bit vCPUs on systems with mismatched EL0 support

From: Marc Zyngier <[email-masked]>
Date: Fri, 27 Nov 2020 10:26:47 +0000

On 2020-11-24 15:50, Will Deacon wrote:
> If a vCPU is caught running 32-bit code on a system with mismatched
> support at EL0, then we should kill it.
> 
> Acked-by: Marc Zyngier <[email-masked]>
> Signed-off-by: Will Deacon <[email-masked]>
> ---
>  arch/arm64/kvm/arm.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 5750ec34960e..d322ac0f4a8e 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -633,6 +633,15 @@ static void check_vcpu_requests(struct kvm_vcpu 
> *vcpu)
>  	}
>  }
> 
> +static bool vcpu_mode_is_bad_32bit(struct kvm_vcpu *vcpu)
> +{
> +	if (likely(!vcpu_mode_is_32bit(vcpu)))
> +		return false;
> +
> +	return !system_supports_32bit_el0() ||
> +		static_branch_unlikely(&arm64_mismatched_32bit_el0);
> +}
> +
>  /**
>   * kvm_arch_vcpu_ioctl_run - the main VCPU run function to execute 
> guest code
>   * @vcpu:	The VCPU pointer
> @@ -816,7 +825,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
>  		 * with the asymmetric AArch32 case), return to userspace with
>  		 * a fatal error.
>  		 */
> -		if (!system_supports_32bit_el0() && vcpu_mode_is_32bit(vcpu)) {
> +		if (vcpu_mode_is_bad_32bit(vcpu)) {
>  			/*
>  			 * As we have caught the guest red-handed, decide that
>  			 * it isn't fit for purpose anymore by making the vcpu

Given the new definition of system_supports_32bit_el0() in the previous 
patch,
why do we need this patch at all?

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

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