Re: [PATCH v2 5/8] KVM: arm64: Add host and hypervisor vCPU lookup primitives

[Vincent Donnefort <vdonnefort@google.com>]

On Fri, Jun 19, 2026 at 08:07:16AM +0100, Fuad Tabba wrote:
> From: Marc Zyngier <maz@kernel.org>
> 
> The nVHE hypervisor repeatedly resolves a host vCPU into the EL2
> address space and validates that the loaded hyp vCPU matches it, with
> that logic open-coded in each handler.
> 
> Add __get_host_hyp_vcpus() and the get_host_hyp_vcpus() macro, which
> translate the host vCPU into the hypervisor's address space and, when
> pKVM is enabled, also return the loaded hyp vCPU if it matches. If pKVM
> is enabled but the loaded hyp vCPU does not correspond to the requested
> host vCPU, both the host and hyp vCPU are returned as NULL. Convert
> handle___kvm_vcpu_run() to use it.
> 
> No functional change intended.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> Co-developed-by: Fuad Tabba <tabba@google.com>
> Signed-off-by: Fuad Tabba <tabba@google.com>

Reviewed-by: Vincent Donnefort <vdonnefort@google.com>

> ---
>  arch/arm64/kvm/hyp/nvhe/hyp-main.c | 52 ++++++++++++++++++++++--------
>  1 file changed, 38 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> index 1d01c6e547f5..8923f594c264 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> @@ -212,14 +212,45 @@ static void handle___pkvm_vcpu_put(struct kvm_cpu_context *host_ctxt)
>  		pkvm_put_hyp_vcpu(hyp_vcpu);
>  }
>  
> -static void handle___kvm_vcpu_run(struct kvm_cpu_context *host_ctxt)
> +static struct kvm_vcpu *__get_host_hyp_vcpus(struct kvm_vcpu *arg,
> +					     struct pkvm_hyp_vcpu **hyp_vcpup)
>  {
> -	DECLARE_REG(struct kvm_vcpu *, host_vcpu, host_ctxt, 1);
> -	int ret;
> +	struct kvm_vcpu *host_vcpu = kern_hyp_va(arg);
> +	struct pkvm_hyp_vcpu *hyp_vcpu = NULL;
>  
>  	if (unlikely(is_protected_kvm_enabled())) {
> -		struct pkvm_hyp_vcpu *hyp_vcpu = pkvm_get_loaded_hyp_vcpu();
> +		hyp_vcpu = pkvm_get_loaded_hyp_vcpu();
>  
> +		if (!hyp_vcpu || hyp_vcpu->host_vcpu != host_vcpu) {
> +			hyp_vcpu = NULL;
> +			host_vcpu = NULL;
> +		}
> +	}
> +
> +	*hyp_vcpup = hyp_vcpu;
> +	return host_vcpu;
> +}
> +
> +#define get_host_hyp_vcpus(ctxt, regnr, hyp_vcpup)			\
> +	({								\
> +		DECLARE_REG(struct kvm_vcpu *, __vcpu, ctxt, regnr);	\
> +		__get_host_hyp_vcpus(__vcpu, hyp_vcpup);		\
> +	})
> +
> +static void handle___kvm_vcpu_run(struct kvm_cpu_context *host_ctxt)
> +{
> +	struct pkvm_hyp_vcpu *hyp_vcpu;
> +	struct kvm_vcpu *host_vcpu;
> +	int ret;
> +
> +	host_vcpu = get_host_hyp_vcpus(host_ctxt, 1, &hyp_vcpu);
> +
> +	if (!host_vcpu) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	if (unlikely(hyp_vcpu)) {
>  		/*
>  		 * KVM (and pKVM) doesn't support SME guests for now, and
>  		 * ensures that SME features aren't enabled in pstate when
> @@ -231,23 +262,16 @@ static void handle___kvm_vcpu_run(struct kvm_cpu_context *host_ctxt)
>  			goto out;
>  		}
>  
> -		if (!hyp_vcpu) {
> -			ret = -EINVAL;
> -			goto out;
> -		}
> -
>  		flush_hyp_vcpu(hyp_vcpu);
>  
>  		ret = __kvm_vcpu_run(&hyp_vcpu->vcpu);
>  
>  		sync_hyp_vcpu(hyp_vcpu);
>  	} else {
> -		struct kvm_vcpu *vcpu = kern_hyp_va(host_vcpu);
> -
>  		/* The host is fully trusted, run its vCPU directly. */
> -		fpsimd_lazy_switch_to_guest(vcpu);
> -		ret = __kvm_vcpu_run(vcpu);
> -		fpsimd_lazy_switch_to_host(vcpu);
> +		fpsimd_lazy_switch_to_guest(host_vcpu);
> +		ret = __kvm_vcpu_run(host_vcpu);
> +		fpsimd_lazy_switch_to_host(host_vcpu);
>  	}
>  out:
>  	cpu_reg(host_ctxt, 1) =  ret;
> -- 
> 2.55.0.rc0.738.g0c8ab3ebcc-goog
>