linux-kernel - Re: [PATCHv4 09/11] KVM: SVM: Add VNMI bit definition

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Message-ID: <ZBujUGXG0JlOLEBh@google.com>
Date:   Wed, 22 Mar 2023 17:54:40 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Santosh Shukla <santosh.shukla@....com>
Cc:     kvm@...r.kernel.org, pbonzini@...hat.com, jmattson@...gle.com,
        joro@...tes.org, linux-kernel@...r.kernel.org,
        mail@...iej.szmigiero.name, mlevitsk@...hat.com,
        thomas.lendacky@....com, vkuznets@...hat.com
Subject: Re: [PATCHv4 09/11] KVM: SVM: Add VNMI bit definition

On Mon, Feb 27, 2023, Santosh Shukla wrote:
> VNMI exposes 3 capability bits (V_NMI, V_NMI_MASK, and V_NMI_ENABLE) to
> virtualize NMI and NMI_MASK, Those capability bits are part of
> VMCB::intr_ctrl -
> V_NMI_PENDING_MASK(11) - Indicates whether a virtual NMI is pending in the
> guest.
> V_NMI_BLOCKING_MASK(12) - Indicates whether virtual NMI is masked in the
> guest.
> V_NMI_ENABLE_MASK(26) - Enables the NMI virtualization feature for the
> guest.

This is way harder to read than it needs to be.  The intent of the various rules
for line length and whatnot is to make code/changelogs easier to read.  That intent
is lost if code/changelogs are written without actually considering the rules.
In other words, don't write changeloges, comments, etc. without thinking about how
the result will look when the line length rules apply.

    Add defines for three new bits in VMVC::int_ctrl that are part of SVM's
    Virtual NMI (vNMI) support:
    
      V_NMI_PENDING_MASK(11)  - Virtual NMI is pending
      V_NMI_BLOCKING_MASK(12) - Virtual NMI is masked
      V_NMI_ENABLE_MASK(26)   - Enable NMI virtualization
    
    To "inject" an NMI, the hypervisor (KVM) sets V_NMI_PENDING.  When the
    CPU services the pending vNMI, hardware clears V_NMI_PENDING and sets
    V_NMI_BLOCKING, e.g. to indicate that the vCPU is handling an NMI.
    Hardware clears V_NMI_BLOCKING upon successful execution of IRET, or if a
    VM-Exit occurs while delivering the virtual NMI.