linux-kernel - Re: [PATCH v2 1/5] KVM: nSVM: deal with L1 hypervisor that intercepts interrupts but lets L2 control EFLAGS.IF

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Message-ID: <6ce77eaf-ed2e-9092-0822-84caddd4a80c@redhat.com>
Date:   Mon, 13 Dec 2021 14:15:51 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     Jim Mattson <jmattson@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Joerg Roedel <joro@...tes.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v2 1/5] KVM: nSVM: deal with L1 hypervisor that intercepts
 interrupts but lets L2 control EFLAGS.IF

On 12/13/21 14:07, Maxim Levitsky wrote:
>> Right, another case is when CLGI is not trapped and the guest therefore
>> runs with GIF=0.  I think that means that a similar change has to be
>> done in all the *_allowed functions.
>
> I think that SVM sets real GIF to 1 on VMentry regardless if it is trapped or not.

Yes, the issue is only when CLGI is not trapped (and vGIF is disabled).

> However if not trapped, and neither EFLAGS.IF is trapped, one could enter a guest
> that has EFLAGS.IF == 0, then the guest could disable GIF, enable EFLAGS.IF,
> and then enable GIF, but then GIF enablement should trigger out interrupt window
> VINTR as well.

While GIF=0 you have svm_nmi_blocked returning true and svm_nmi_allowed 
returning -EBUSY; that's wrong isn't it?

Paolo