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

From: Paolo Bonzini <pbonzini@redhat.com>
To: Maxim Levitsky <mlevitsk@redhat.com>, kvm@vger.kernel.org
Cc: Wanpeng Li <wanpengli@tencent.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
	<linux-kernel@vger.kernel.org>, Jim Mattson <jmattson@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@alien8.de>,
	Joerg Roedel <joro@8bytes.org>, Ingo Molnar <mingo@redhat.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, Sean Christopherson <seanjc@google.com>,
	Cathy Avery <cavery@redhat.com>
Subject: Re: [PATCH 4/5] KVM: nSVM: force L1's GIF to 1 when setting the nested state
Date: Mon, 3 May 2021 16:00:47 +0200	[thread overview]
Message-ID: <7d2fe4a1-9603-8bea-e7f1-fb3c24198941@redhat.com> (raw)
In-Reply-To: <20210503125446.1353307-5-mlevitsk@redhat.com>

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@redhat.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