linux-kernel - Re: [PATCH v2 03/22] KVM: SVM: immediately inject INTR vmexit

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Date:   Thu, 21 May 2020 14:50:57 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     wei.huang2@....com, cavery@...hat.com,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Oliver Upton <oupton@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v2 03/22] KVM: SVM: immediately inject INTR vmexit

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

> We can immediately leave SVM guest mode in svm_check_nested_events
> now that we have the nested_run_pending mechanism.  This makes
> things easier because we can run the rest of inject_pending_event
> with GIF=0, and KVM will naturally end up requesting the next
> interrupt window.
>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/svm/nested.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index e69e60ac1370..266fde240493 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -778,13 +778,13 @@ int nested_svm_check_exception(struct vcpu_svm *svm, unsigned nr,
>  
>  static void nested_svm_intr(struct vcpu_svm *svm)
>  {
> +	trace_kvm_nested_intr_vmexit(svm->vmcb->save.rip);
> +
>  	svm->vmcb->control.exit_code   = SVM_EXIT_INTR;
>  	svm->vmcb->control.exit_info_1 = 0;
>  	svm->vmcb->control.exit_info_2 = 0;
>  
> -	/* nested_svm_vmexit this gets called afterwards from handle_exit */
> -	svm->nested.exit_required = true;
> -	trace_kvm_nested_intr_vmexit(svm->vmcb->save.rip);
> +	nested_svm_vmexit(svm);
>  }
>  
>  static bool nested_exit_on_intr(struct vcpu_svm *svm)

Sorry for reporting this late but I just found out that this commit
breaks Hyper-V 2016 on KVM on SVM completely (always hangs on boot). I
haven't investigated it yet (well, this is Windows, you know...) but
what's usually different about Hyper-V is that unlike KVM/Linux it has
handlers for some hardware interrupts in the guest and not in the
hypervisor.

-- 
Vitaly