linux-kernel - Re: [PATCH v2 10/18] arm64: KVM/debug: use EL1&0 stage 1 translation regime

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Date:   Sun, 22 Dec 2019 10:34:55 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Andrew Murray <andrew.murray@....com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Sudeep Holla <sudeep.holla@....com>,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 10/18] arm64: KVM/debug: use EL1&0 stage 1 translation regime

On Fri, 20 Dec 2019 14:30:17 +0000,
Andrew Murray <andrew.murray@....com> wrote:
> 
> From: Sudeep Holla <sudeep.holla@....com>
> 
> Now that we have all the save/restore mechanism in place, lets enable
> the translation regime used by buffer from EL2 stage 1 to EL1 stage 1
> on VHE systems.
> 
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> [ Reword commit, don't trap to EL2 ]

Not trapping to EL2 for the case where we don't allow SPE in the
guest is not acceptable.

> Signed-off-by: Andrew Murray <andrew.murray@....com>
> ---
>  arch/arm64/kvm/hyp/switch.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index 67b7c160f65b..6c153b79829b 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -100,6 +100,7 @@ static void activate_traps_vhe(struct kvm_vcpu *vcpu)
>  
>  	write_sysreg(val, cpacr_el1);
>  
> +	write_sysreg(vcpu->arch.mdcr_el2 | 3 << MDCR_EL2_E2PB_SHIFT, mdcr_el2);
>  	write_sysreg(kvm_get_hyp_vector(), vbar_el1);
>  }
>  NOKPROBE_SYMBOL(activate_traps_vhe);
> @@ -117,6 +118,7 @@ static void __hyp_text __activate_traps_nvhe(struct kvm_vcpu *vcpu)
>  		__activate_traps_fpsimd32(vcpu);
>  	}
>  
> +	write_sysreg(vcpu->arch.mdcr_el2 | 3 << MDCR_EL2_E2PB_SHIFT, mdcr_el2);

There is a _MASK macro that can replace this '3', and is in keeping
with the rest of the code.

It still remains that it looks like the wrong place to do this, and
vcpu_load seems much better. Why should you write to mdcr_el2 on each
entry to the guest, since you know whether it has SPE enabled at the
point where it gets scheduled?

	M.

-- 
Jazz is not dead, it just smells funny.