Re: [PATCH v3] KVM: x86: Fix the intel_pt PMI handling wrongly considered from guest

[Yanfei Xu]

On 2022/5/24 00:43, Sean Christopherson wrote:
> On Mon, May 23, 2022, Yanfei Xu wrote:
> > When kernel handles the vm-exit caused by external interrupts and NMI,
> > it always set a type of kvm_intr_type to handling_intr_from_guest to
> > tell if it's dealing an IRQ or NMI. For the PMI scenario, it could be
> > IRQ or NMI.
> > However the intel_pt PMI certainly is a NMI PMI, hence using
> It'd be helpful for future readers to explain why it's guaranteed to an NMI.  E.g.
>
> However, intel_pt PMIs are only generated for HARDWARE perf events, and
> HARDWARE events are always configured to generate NMIs.  Use
> kvm_handling_nmi_from_guest() to precisely identify if the intel_pt PMI
> came from the guest to avoid false positives if an intel_pt PMI/NMI
> arrives while the host is handling an unrelated IRQ VM-Exit.

It's much better!

> > kvm_handling_nmi_from_guest() to distinguish if the intel_pt PMI comes
> > from guest is more appropriate. This modification can avoid the host
> > wrongly considered the intel_pt PMI comes from a guest once the host
> > intel_pt PMI breaks the handling of vm-exit of external interrupts.
> >
> > Fixes: db215756ae59 ("KVM: x86: More precisely identify NMI from guest when handling PMI")
> > Signed-off-by: Yanfei Xu <yanfei.xu@xxxxxxxxx>
> > ---
> > v1->v2:
> > 1.Fix vmx_handle_intel_pt_intr() directly instead of changing the generic function.
> > 2.Tune the commit message.
> >
> > v2->v3:
> > Add the NULL pointer check of variable "vcpu".
> >
> >   arch/x86/kvm/vmx/vmx.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > index 610355b9ccce..982df9c000d3 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -7856,7 +7856,7 @@ static unsigned int vmx_handle_intel_pt_intr(void)
> >   	struct kvm_vcpu *vcpu = kvm_get_running_vcpu();
> >   
> >   	/* '0' on failure so that the !PT case can use a RET0 static call. */
> > -	if (!kvm_arch_pmi_in_guest(vcpu))
> > +	if (!vcpu || !kvm_handling_nmi_from_guest(vcpu))
> Alternatively,
>
> 	if (!kvm_arch_pmi_in_guest(vcpu) || !kvm_handling_nmi_from_guest(vcpu))
>
> The generated code is the same since the compiler is smart enough to elide the
> handling_intr_from_guest check from kvm_arch_pmi_in_guest.
>
> I'm not actually sure that's better than the !vcpu check though, e.g. it hides the
> not-NULL aspect of the check.
>
> Either way, with a tweaked changelog,
>
> Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Thanks Sean.

Regards,
Yanfei