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

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Message-ID: <Y3uzAM3/XrUPRpgH@google.com>
Date:   Mon, 21 Nov 2022 17:18:56 +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 Mon, Nov 21, 2022, Maxim Levitsky wrote:
> On Thu, 2022-11-17 at 18:54 +0000, Sean Christopherson wrote:
> > E.g. with HF_NMI_MASK => svm->nmi_masked, the end result can be something like:
> > 
> > static bool __is_vnmi_enabled(struct *vmcb)
> > {
> >         return !!(vmcb->control.int_ctl & V_NMI_ENABLE);
> > }
> > 
> > static bool is_vnmi_enabled(struct vcpu_svm *svm)
> > {
> >         struct vmcb *vmcb = get_vnmi_vmcb(svm);
> > 
> >         return vmcb && __is_vnmi_enabled(vmcb);
> > }
> > 
> > static bool svm_get_nmi_mask(struct kvm_vcpu *vcpu)
> > {
> >         struct vcpu_svm *svm = to_svm(vcpu);
> >         struct vmcb *vmcb = get_vnmi_vmcb(svm);
> > 
> >         if (vmcb && __is_vnmi_enabled(vmcb))
> >                 return !!(vmcb->control.int_ctl & V_NMI_MASK);
> >         else
> >                 return !!(vcpu->arch.hflags & HF_NMI_MASK);
> > }
> > 
> > static void svm_set_or_clear_vnmi_mask(struct vmcb *vmcb, bool set)
> > {
> >         if (set)
> >                 vmcb->control.int_ctl |= V_NMI_MASK;
> >         else
> >                 vmcb->control.int_ctl &= ~V_NMI_MASK;
> > }
> > 
> > static void svm_set_nmi_mask(struct kvm_vcpu *vcpu, bool masked)
> > {
> >         struct vcpu_svm *svm = to_svm(vcpu);
> >         struct vmcb *vmcb = get_vnmi_vmcb(svm);
> > 
> >         if (vmcb && __is_vnmi_enabled(vmcb)) {
> >                 if (masked)
> >                         vmcb->control.int_ctl |= V_NMI_MASK;
> >                 else
> >                         vmcb->control.int_ctl &= ~V_NMI_MASK;
> >         } else {
> >                 svm->nmi_masked = masked;
> >         }
> > 
> >         if (!masked)
> >                 svm_disable_iret_interception(svm);
> > }
> 
> OK, this is one of the ways to do it, makes sense overall.
> I actualy wanted to do something like that but opted to not touch
> the original code too much, but only what I needed. I can do this
> in a next version.

After looking at more of this code, I think having get_vnmi_vmcb() is a mistake.
It just ends up being a funky wrapper to the current svm->vmcb.  And the manual
check on the "vnmi" global is pointless.  If KVM sets V_NMI_ENABLE in any VMCB
when vnmi=false, then that's a KVM bug.

Dropping the wrapper eliminates the possibility of a NULL VMCB pointer, and IMO
yields far more readable code.


static bool is_vnmi_enabled(struct vcpu_svm *svm)
{
	return !!(svm->vmcb->control.int_ctl & V_NMI_ENABLE);
}

static bool svm_get_nmi_mask(struct kvm_vcpu *vcpu)
{
	struct vcpu_svm *svm = to_svm(vcpu);

	if (is_vnmi_enabled(svm))
		return !!(svm->vmcb->control.int_ctl & V_NMI_MASK);
	else
		return !!(vcpu->arch.hflags & HF_NMI_MASK);
}

static void svm_set_nmi_mask(struct kvm_vcpu *vcpu, bool masked)
{
	struct vcpu_svm *svm = to_svm(vcpu);

	if (is_vnmi_enabled(svm)) {
		if (masked)
			svm->vmcb->control.int_ctl |= V_NMI_MASK;
		else
			svm->vmcb->control.int_ctl &= ~V_NMI_MASK;
	} else {
		svm->nmi_masked = masked;
	}

	if (!masked)
		svm_disable_iret_interception(svm);
}