linux-kernel - Re: [PATCH 03/16] KVM: arm64: Avoid remapping the SVE state in the hyp stage-1

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Date:   Sat, 16 Oct 2021 12:04:15 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Quentin Perret <qperret@...gle.com>
Cc:     James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Fuad Tabba <tabba@...gle.com>,
        David Brazdil <dbrazdil@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH 03/16] KVM: arm64: Avoid remapping the SVE state in the hyp stage-1

On Wed, 13 Oct 2021 16:58:18 +0100,
Quentin Perret <qperret@...gle.com> wrote:
> 
> We currently map the SVE state into the hypervisor stage-1 on VCPU_RUN,
> when the vCPU thread's PID has changed. However, this only needs to be
> done during the first VCPU_RUN as the SVE state doesn't depend on
> thread-specific data, so move the create_hyp_mapping() call to
> kvm_vcpu_first_run_init().
> 
> Suggested-by: Marc Zyngier <maz@...nel.org>
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> ---
>  arch/arm64/kvm/arm.c    | 12 ++++++++++++
>  arch/arm64/kvm/fpsimd.c | 11 -----------
>  2 files changed, 12 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index fe102cd2e518..c33d8c073820 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -618,6 +618,18 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu)
>  	if (ret)
>  		return ret;
>  
> +	if (vcpu->arch.sve_state) {
> +		void *sve_end;
> +
> +		sve_end = vcpu->arch.sve_state + vcpu_sve_state_size(vcpu);
> +
> +		ret = create_hyp_mappings(vcpu->arch.sve_state, sve_end,
> +					  PAGE_HYP);
> +		if (ret)
> +			return ret;
> +	}
> +
> +
>  	ret = kvm_arm_pmu_v3_enable(vcpu);
>  
>  	return ret;
> diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
> index 5621020b28de..62c0d78da7be 100644
> --- a/arch/arm64/kvm/fpsimd.c
> +++ b/arch/arm64/kvm/fpsimd.c
> @@ -43,17 +43,6 @@ int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu)
>  	if (ret)
>  		goto error;
>  
> -	if (vcpu->arch.sve_state) {
> -		void *sve_end;
> -
> -		sve_end = vcpu->arch.sve_state + vcpu_sve_state_size(vcpu);
> -
> -		ret = create_hyp_mappings(vcpu->arch.sve_state, sve_end,
> -					  PAGE_HYP);
> -		if (ret)
> -			goto error;
> -	}
> -
>  	vcpu->arch.host_thread_info = kern_hyp_va(ti);
>  	vcpu->arch.host_fpsimd_state = kern_hyp_va(fpsimd);
>  error:

I actually ended-up implementing a similar patch as part of my 'first
run' series[1], though I moved the mapping to the point where we
finalise the vcpu as that's where the allocation takes place.

Do you see any potential issue with that approach?

Thanks,

	M.

[1] https://lore.kernel.org/r/20211015090822.2994920-2-maz@kernel.org

-- 
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