linux-kernel - Re: [PATCH 1/4] KVM: nSVM: do not change host intercepts while nested VM is running

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Message-ID: <87a74tee8p.fsf@vitty.brq.redhat.com>
Date:   Fri, 06 Mar 2020 15:42:46 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     cavery@...hat.com, jan.kiszka@...mens.com, wei.huang2@....com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH 1/4] KVM: nSVM: do not change host intercepts while nested VM is running

Paolo Bonzini <pbonzini@...hat.com> writes:

> Instead of touching the host intercepts so that the bitwise OR in
> recalc_intercepts just works, mask away uninteresting intercepts
> directly in recalc_intercepts.
>
> This is cleaner and keeps the logic in one place even for intercepts
> that can change even while L2 is running.
>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/svm.c | 31 ++++++++++++++++++-------------
>  1 file changed, 18 insertions(+), 13 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 247e31d21b96..14cb5c194008 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -519,10 +519,24 @@ static void recalc_intercepts(struct vcpu_svm *svm)
>  	h = &svm->nested.hsave->control;
>  	g = &svm->nested;
>  
> -	c->intercept_cr = h->intercept_cr | g->intercept_cr;
> -	c->intercept_dr = h->intercept_dr | g->intercept_dr;
> -	c->intercept_exceptions = h->intercept_exceptions | g->intercept_exceptions;
> -	c->intercept = h->intercept | g->intercept;
> +	c->intercept_cr = h->intercept_cr;
> +	c->intercept_dr = h->intercept_dr;
> +	c->intercept_exceptions = h->intercept_exceptions;
> +	c->intercept = h->intercept;
> +
> +	if (svm->vcpu.arch.hflags & HF_VINTR_MASK) {
> +		/* We only want the cr8 intercept bits of L1 */
> +		c->intercept_cr &= ~(1U << INTERCEPT_CR8_READ);
> +		c->intercept_cr &= ~(1U << INTERCEPT_CR8_WRITE);
> +	}
> +
> +	/* We don't want to see VMMCALLs from a nested guest */
> +	c->intercept &= ~(1ULL << INTERCEPT_VMMCALL);
> +
> +	c->intercept_cr |= g->intercept_cr;
> +	c->intercept_dr |= g->intercept_dr;
> +	c->intercept_exceptions |= g->intercept_exceptions;
> +	c->intercept |= g->intercept;
>  }
>  
>  static inline struct vmcb *get_host_vmcb(struct vcpu_svm *svm)
> @@ -3590,15 +3604,6 @@ static void enter_svm_guest_mode(struct vcpu_svm *svm, u64 vmcb_gpa,
>  	else
>  		svm->vcpu.arch.hflags &= ~HF_VINTR_MASK;
>  
> -	if (svm->vcpu.arch.hflags & HF_VINTR_MASK) {
> -		/* We only want the cr8 intercept bits of the guest */
> -		clr_cr_intercept(svm, INTERCEPT_CR8_READ);
> -		clr_cr_intercept(svm, INTERCEPT_CR8_WRITE);
> -	}
> -
> -	/* We don't want to see VMMCALLs from a nested guest */
> -	clr_intercept(svm, INTERCEPT_VMMCALL);
> -
>  	svm->vcpu.arch.tsc_offset += nested_vmcb->control.tsc_offset;
>  	svm->vmcb->control.tsc_offset = svm->vcpu.arch.tsc_offset;

FWIW,

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly