linux-kernel - Re: [PATCH 07/13] KVM: SVM: Add VNMI support in get/set_nmi

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Message-ID: <Y4+JeAiT8IpTXux9@google.com>
Date:   Tue, 6 Dec 2022 18:27:04 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sandipan Das <sandipan.das@....com>,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        Jing Liu <jing2.liu@...el.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Wyes Karny <wyes.karny@....com>,
        Borislav Petkov <bp@...en8.de>,
        Babu Moger <babu.moger@....com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Jim Mattson <jmattson@...gle.com>, x86@...nel.org,
        Santosh Shukla <santosh.shukla@....com>
Subject: Re: [PATCH 07/13] KVM: SVM: Add VNMI support in get/set_nmi_mask

On Sun, Dec 04, 2022, Maxim Levitsky wrote:
> For vNMI case it turns out that we don't need to intercept IRET at all after all:
> 
> Turns out that when vNMI is pending, you can still EVENTINJ another NMI, and
> the pending vNMI will be kept pending, vNMI will became masked due to
> EVENTINJ, and on IRET the pending vNMI will be serviced as well, so in total
> both NMIs will be serviced.

I believe past me was thinking that the "merging" of pending NMIs happened in the
context of the sender, but it always happens in the context of the target vCPU.
Senders always do KVM_REQ_NMI, i.e. always kick if the vCPU in running, which gives
KVM the hook it needs to update the VMCB.

So yeah, as long as KVM can stuff two NMIs into the VMCB, I think we're good.
I'll give the series a proper review in the next week or so.