linux-kernel - RE: [PATCH] KVM: x86: Fix the intel_pt PMI handling wrongly considered from guest

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Date:   Sat, 21 May 2022 04:31:34 +0000
From:   "Xu, Yanfei" <yanfei.xu@...el.com>
To:     "Christopherson,, Sean" <seanjc@...gle.com>
CC:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "wanpengli@...cent.com" <wanpengli@...cent.com>,
        "jmattson@...gle.com" <jmattson@...gle.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Wang, Wei W" <wei.w.wang@...el.com>,
        "Liang, Kan" <kan.liang@...el.com>
Subject: RE: [PATCH] KVM: x86: Fix the intel_pt PMI handling wrongly
 considered from guest



> -----Original Message-----
> From: Sean Christopherson <seanjc@...gle.com>
> Sent: Saturday, May 21, 2022 12:32 AM
> To: Xu, Yanfei <yanfei.xu@...el.com>
> Cc: pbonzini@...hat.com; vkuznets@...hat.com; wanpengli@...cent.com;
> jmattson@...gle.com; joro@...tes.org; tglx@...utronix.de;
> mingo@...hat.com; bp@...en8.de; dave.hansen@...ux.intel.com;
> x86@...nel.org; kvm@...r.kernel.org; linux-kernel@...r.kernel.org; Wang,
> Wei W <wei.w.wang@...el.com>; Liang, Kan <kan.liang@...el.com>
> Subject: Re: [PATCH] KVM: x86: Fix the intel_pt PMI handling wrongly considered
> from guest
> 
> Please don't top-post.
Got it, just correctly configured my mailbox with prefix each line of original message.

> 
> On Fri, May 20, 2022, Xu, Yanfei wrote:
> > From: Sean Christopherson <seanjc@...gle.com> On Mon, May 16, 2022,
> > Yanfei Xu wrote:
> > > diff --git a/arch/x86/include/asm/kvm_host.h
> > > b/arch/x86/include/asm/kvm_host.h index 4ff36610af6a..308cf19f123d
> > > 100644
> > > --- a/arch/x86/include/asm/kvm_host.h
> > > +++ b/arch/x86/include/asm/kvm_host.h
> > > @@ -1582,8 +1582,14 @@ static inline int
> kvm_arch_flush_remote_tlb(struct kvm *kvm)
> > >  		return -ENOTSUPP;
> > >  }
> > >
> > > +enum kvm_intr_type {
> > > +	/* Values are arbitrary, but must be non-zero. */
> > > +	KVM_HANDLING_IRQ = 1,
> > > +	KVM_HANDLING_NMI,
> > > +};
> > > +
> > >  #define kvm_arch_pmi_in_guest(vcpu) \
> > > -	((vcpu) && (vcpu)->arch.handling_intr_from_guest)
> > > +	((vcpu) && (vcpu)->arch.handling_intr_from_guest ==
> > > +KVM_HANDLING_NMI)
> >
> > My understanding is that this isn't correct as a general change, as
> > perf events can use regular IRQs in some cases.  See commit dd60d217062f4
> ("KVM:
> > x86: Fix perf timer mode IP reporting").
> >
> > I assume there's got to be a way to know which mode perf is using,
> > e.g. we should be able to make this look something like:
> >
> > 	((vcpu) && (vcpu)->arch.handling_intr_from_guest == kvm_pmi_vector)
> 
> > Hi Sean,
> > You are right, the change of kvm_arch_pmi_in_guest is incorrect, because it
> should cover two cases of PMI.
> > For the PMI of intel pt, it certainly is the NMI PMI. So how about fixing it like
> below?
> 
> Yep, that works.  I did enough spelunking to figure out how we can fix the
> generic issue, but it's per-event and requires a decent amount of plumbing in
> perf.

Agree, it's per-event for the generic issue...
> 
> perf_guest_handle_intel_pt_intr() doesn't bother with perf_guest_state() since
> it's such a specialized event, so fixing this in vmx_handle_intel_pt_intr() would
> likely be the long-term solution even if/when the generic case is fixed.

Will send the v2.

Thanks,
Yanfei