linux-kernel - Re: [PATCH 20/30] KVM: SVM: preserve VGIF across VMCB switch

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Date:   Sun, 31 May 2020 16:11:36 -0700
From:   Krish Sadhukhan <krish.sadhukhan@...cle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH 20/30] KVM: SVM: preserve VGIF across VMCB switch


On 5/29/20 8:39 AM, Paolo Bonzini wrote:
> There is only one GIF flag for the whole processor, so make sure it is not clobbered
> when switching to L2 (in which case we also have to include the V_GIF_ENABLE_MASK,
> lest we confuse enable_gif/disable_gif/gif_set).  When going back, L1 could in
> theory have entered L2 without issuing a CLGI so make sure the svm_set_gif is
> done last, after svm->vmcb->control.int_ctl has been copied back from hsave.
>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>   arch/x86/kvm/svm/nested.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 7e4a506828c9..6c7f0bffdf01 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -293,6 +293,7 @@ static void nested_prepare_vmcb_save(struct vcpu_svm *svm, struct vmcb *nested_v
>   
>   static void nested_prepare_vmcb_control(struct vcpu_svm *svm)
>   {
> +	const u32 mask = V_INTR_MASKING_MASK | V_GIF_ENABLE_MASK | V_GIF_MASK;
>   	if (svm->nested.ctl.nested_ctl & SVM_NESTED_CTL_NP_ENABLE)
>   		nested_svm_init_mmu_context(&svm->vcpu);
>   
> @@ -308,7 +309,10 @@ static void nested_prepare_vmcb_control(struct vcpu_svm *svm)
>   	svm->vmcb->control.tsc_offset = svm->vcpu.arch.tsc_offset =
>   		svm->vcpu.arch.l1_tsc_offset + svm->nested.ctl.tsc_offset;
>   
> -	svm->vmcb->control.int_ctl             = svm->nested.ctl.int_ctl | V_INTR_MASKING_MASK;
> +	svm->vmcb->control.int_ctl             =
> +		(svm->nested.ctl.int_ctl & ~mask) |
> +		(svm->nested.hsave->control.int_ctl & mask);


If this is the very first VMRUN, do we have any int_ctl saved in hsave ?

> +
>   	svm->vmcb->control.virt_ext            = svm->nested.ctl.virt_ext;
>   	svm->vmcb->control.int_vector          = svm->nested.ctl.int_vector;
>   	svm->vmcb->control.int_state           = svm->nested.ctl.int_state;