Re: [PATCH 2/4] KVM: arm64: ensure guest access to CTR_EL0 is trapped

From: Marc Zyngier <maz@kernel.org>
To: Sebastian Ott <sebott@redhat.com>
Cc: linux-arm-kernel@lists.infradead.org,
	Oliver Upton <oliver.upton@linux.dev>
Subject: Re: [PATCH 2/4] KVM: arm64: ensure guest access to CTR_EL0 is trapped
Date: Mon, 18 Mar 2024 11:47:14 +0000	[thread overview]
Message-ID: <861q87224d.wl-maz@kernel.org> (raw)
In-Reply-To: <20240318111636.10613-3-sebott@redhat.com>

On Mon, 18 Mar 2024 11:16:34 +0000,
Sebastian Ott <sebott@redhat.com> wrote:
> 
> Ensure that guest access to the CTR_EL0 register is trapped
> independent of cpu errata.
> 
> Signed-off-by: Sebastian Ott <sebott@redhat.com>
> ---
>  arch/arm64/include/asm/kvm_emulate.h | 7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index b804fe832184..daaaf7664219 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -91,12 +91,7 @@ static inline void vcpu_reset_hcr(struct kvm_vcpu *vcpu)
>  		vcpu->arch.hcr_el2 |= HCR_TVM;
>  	}
>  
> -	if (cpus_have_final_cap(ARM64_HAS_EVT) &&
> -	    !cpus_have_final_cap(ARM64_MISMATCHED_CACHE_TYPE))
> -		vcpu->arch.hcr_el2 |= HCR_TID4;
> -	else
> -		vcpu->arch.hcr_el2 |= HCR_TID2;
> -
> +	vcpu->arch.hcr_el2 |= HCR_TID2;

NAK. This is a huge performance sync. You should only revert to this
when absolutely necessary.

	M.

-- 
Without deviation from the norm, progress is not possible.

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