linux-kernel - Re: [PATCH 4/5] KVM: nSVM: force L1's GIF to 1 when setting the nested state

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Date:   Mon, 3 May 2021 16:00:47 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>, Jim Mattson <jmattson@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Joerg Roedel <joro@...tes.org>, Ingo Molnar <mingo@...hat.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Cathy Avery <cavery@...hat.com>
Subject: Re: [PATCH 4/5] KVM: nSVM: force L1's GIF to 1 when setting the
 nested state

On 03/05/21 14:54, Maxim Levitsky wrote:
> While after a reset the GIF value is already 1,
> it doesn't have to have this value if the nested state
> is loaded later.
> 
> Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
> ---
>   arch/x86/kvm/svm/nested.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 32400cba608d..12a12ae940fa 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -1314,6 +1314,9 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
>   	else
>   		svm->nested.vmcb02.ptr->save = svm->vmcb01.ptr->save;
>   
> +	/* Force L1's GIF to true */
> +	svm_set_gif(svm, true);
> +
>   	svm->nested.nested_run_pending =
>   		!!(kvm_state->flags & KVM_STATE_NESTED_RUN_PENDING);
>   
> 

Hmm, not sure about this one.  It is possible in principle to do CLGI in 
L2 with the intercept disabled.

You need to use

svm_set_gif(svm, !!(kvm_state->flags & KVM_STATE_NESTED_GIF_SET));

instead.

Paolo