linux-kernel - Re: [PATCH 6.13 8/8] KVM: arm64: Eagerly switch ZCR

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Message-ID: <Z9qcem7BVeuRd5XD@J2N7QTR9R3>
Date: Wed, 19 Mar 2025 10:29:14 +0000
From: Mark Rutland <mark.rutland@....com>
To: Mark Brown <broonie@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Marc Zyngier <maz@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, Fuad Tabba <tabba@...gle.com>
Subject: Re: [PATCH 6.13 8/8] KVM: arm64: Eagerly switch ZCR_EL{1,2}

On Wed, Mar 12, 2025 at 11:49:16PM +0000, Mark Brown wrote:
> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> index 7262983c75fbc18ab44f52753bff1dd9167a68d3..84326765c66087d992a517a19fea94b04c39c994 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> @@ -5,6 +5,7 @@
>   */
>  
>  #include <hyp/adjust_pc.h>
> +#include <hyp/switch.h>
>  
>  #include <asm/pgtable-types.h>
>  #include <asm/kvm_asm.h>
> @@ -178,8 +179,12 @@ static void handle___kvm_vcpu_run(struct kvm_cpu_context *host_ctxt)
>  		sync_hyp_vcpu(hyp_vcpu);
>  		pkvm_put_hyp_vcpu(hyp_vcpu);
>  	} else {
> +		struct kvm_vcpu *vcpu = kern_hyp_va(host_vcpu);
> +
>  		/* The host is fully trusted, run its vCPU directly. */
> -		ret = __kvm_vcpu_run(host_vcpu);
> +		fpsimd_lazy_switch_to_guest(vcpu);
> +		ret = __kvm_vcpu_run(vcpu);
> +		fpsimd_lazy_switch_to_host(vcpu);
>  	}

As Gavin noted [1] for the v6.12 backport, the addition of kern_hyp_va()
is not correct, since 'host_vcpu' has already been converted to a hyp VA
at this point.

[1] https://lore.kernel.org/linux-arm-kernel/019afc2d-b047-4e33-971c-7debbbaec84d@redhat.com/#t

Mark.