Re: [PATCH] KVM: x86/pt: Do not inject TraceToPAPMI when guest PT isn't supported

[Like Xu]

On 27/5/2021 1:38 am, Sean Christopherson wrote:
> On Fri, May 14, 2021, Like Xu wrote:
> > When a PT perf user is running in system-wide mode on the host,
> > the guest (w/ pt_mode=0) will warn about anonymous NMIs from
> > kvm_handle_intel_pt_intr():
> >
> > [   18.126444] Uhhuh. NMI received for unknown reason 10 on CPU 0.
> > [   18.126447] Do you have a strange power saving mode enabled?
> > [   18.126448] Dazed and confused, but trying to continue
> >
> > In this case, these PMIs should be handled by the host PT handler().
> > When PT is used in guest-only mode, it's harmless to call host handler.
> >
> > Fix: 8479e04e7d("KVM: x86: Inject PMI for KVM guest")
>
> s/Fix/Fixes
>
> > Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
> > ---
> >   arch/x86/events/intel/core.c | 3 +--
> >   arch/x86/kvm/x86.c           | 3 +++
> >   2 files changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> > index 2521d03de5e0..2f09eb0853de 100644
> > --- a/arch/x86/events/intel/core.c
> > +++ b/arch/x86/events/intel/core.c
> > @@ -2853,8 +2853,7 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
> >   		if (unlikely(perf_guest_cbs && perf_guest_cbs->is_in_guest() &&
> >   			perf_guest_cbs->handle_intel_pt_intr))
> >   			perf_guest_cbs->handle_intel_pt_intr();
> > -		else
> > -			intel_pt_interrupt();
> > +		intel_pt_interrupt();
>
> Would it make sense to instead do something like:
>
> 	bool host_pmi = true;
>
> 	...
>
> 		if (unlikely(perf_guest_cbs && perf_guest_cbs->is_in_guest() &&
> 			     perf_guest_cbs->handle_intel_pt_intr)
> 			host_pmi = !perf_guest_cbs->handle_intel_pt_intr();

struct perf_guest_info_callbacks {
	...
	void				(*handle_intel_pt_intr)(void);
};


This fix is deferred until the following proposal is finalized.

https://lore.kernel.org/lkml/YKImQ2%2FDilGIkrfe@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/

> 		if (likely(host_pmi))
> 			intel_pt_interrupt();
> >   	}
> >   
> >   	/*
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 6529e2023147..6660f3948cea 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -8087,6 +8087,9 @@ static void kvm_handle_intel_pt_intr(void)
> >   {
> >   	struct kvm_vcpu *vcpu = __this_cpu_read(current_vcpu);
> >   
> > +	if (!guest_cpuid_has(vcpu, X86_FEATURE_INTEL_PT))
> > +		return;
> > +
> >   	kvm_make_request(KVM_REQ_PMI, vcpu);
> >   	__set_bit(MSR_CORE_PERF_GLOBAL_OVF_CTRL_TRACE_TOPA_PMI_BIT,
> >   			(unsigned long *)&vcpu->arch.pmu.global_status);
> > --
> > 2.31.1