Re: [PATCH v2 2/3] KVM: nVMX: add kvm_nested_vmlaunch_resume tracepoint

[Maxim Levitsky]

On Thu, 2021-01-14 at 16:14 -0800, Sean Christopherson wrote:
> On Thu, Jan 14, 2021, Maxim Levitsky wrote:
> > This is very helpful for debugging nested VMX issues.
> > 
> > Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> > ---
> >  arch/x86/kvm/trace.h      | 30 ++++++++++++++++++++++++++++++
> >  arch/x86/kvm/vmx/nested.c |  6 ++++++
> >  arch/x86/kvm/x86.c        |  1 +
> >  3 files changed, 37 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
> > index 2de30c20bc264..663d1b1d8bf64 100644
> > --- a/arch/x86/kvm/trace.h
> > +++ b/arch/x86/kvm/trace.h
> > @@ -554,6 +554,36 @@ TRACE_EVENT(kvm_nested_vmrun,
> >  		__entry->npt ? "on" : "off")
> >  );
> >  
> > +
> > +/*
> > + * Tracepoint for nested VMLAUNCH/VMRESUME
> 
> VM-Enter, as below.

Will do

> 
> > + */
> > +TRACE_EVENT(kvm_nested_vmlaunch_resume,
> 
> s/vmlaunc_resume/vmenter, both for consistency with other code and so that it
> can sanely be reused by SVM.  IMO, trace_kvm_entry is wrong :-).
SVM already has trace_kvm_nested_vmrun and it contains some SVM specific
stuff that doesn't exist on VMX and vise versa.
So I do want to keep these trace points separate.


> 
> > +	    TP_PROTO(__u64 rip, __u64 vmcs, __u64 nested_rip,
> > +		     __u32 entry_intr_info),
> > +	    TP_ARGS(rip, vmcs, nested_rip, entry_intr_info),
> > +
> > +	TP_STRUCT__entry(
> > +		__field(	__u64,		rip		)
> > +		__field(	__u64,		vmcs		)
> > +		__field(	__u64,		nested_rip	)
> > +		__field(	__u32,		entry_intr_info	)
> > +	),
> > +
> > +	TP_fast_assign(
> > +		__entry->rip			= rip;
> > +		__entry->vmcs			= vmcs;
> > +		__entry->nested_rip		= nested_rip;
> > +		__entry->entry_intr_info	= entry_intr_info;
> > +	),
> > +
> > +	TP_printk("rip: 0x%016llx vmcs: 0x%016llx nrip: 0x%016llx "
> > +		  "entry_intr_info: 0x%08x",
> > +		__entry->rip, __entry->vmcs, __entry->nested_rip,
> > +		__entry->entry_intr_info)
> > +);
> > +
> > +
> >  TRACE_EVENT(kvm_nested_intercepts,
> >  	    TP_PROTO(__u16 cr_read, __u16 cr_write, __u32 exceptions,
> >  		     __u32 intercept1, __u32 intercept2, __u32 intercept3),
> > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> > index 776688f9d1017..cd51b66480d52 100644
> > --- a/arch/x86/kvm/vmx/nested.c
> > +++ b/arch/x86/kvm/vmx/nested.c
> > @@ -3327,6 +3327,12 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
> >  		!(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_BNDCFGS))
> >  		vmx->nested.vmcs01_guest_bndcfgs = vmcs_read64(GUEST_BNDCFGS);
> >  
> > +	trace_kvm_nested_vmlaunch_resume(kvm_rip_read(vcpu),
> 
> Hmm, won't this RIP be wrong for the migration case?  I.e. it'll be L2, not L1
> as is the case for the "true" nested VM-Enter path.

> 
> > +					 vmx->nested.current_vmptr,
> > +					 vmcs12->guest_rip,
> > +					 vmcs12->vm_entry_intr_info_field);
> 
> The placement is a bit funky.  I assume you put it here so that calls from
> vmx_set_nested_state() also get traced.  But, that also means
> vmx_pre_leave_smm() will get traced, and it also creates some weirdness where
> some nested VM-Enters that VM-Fail will get traced, but others will not.
> 
> Tracing vmx_pre_leave_smm() isn't necessarily bad, but it could be confusing,
> especially if the debugger looks up the RIP and sees RSM.  Ditto for the
> migration case.
> 
> Not sure what would be a good answer.
> 
> > +
> > +
> >  	/*
> >  	 * Overwrite vmcs01.GUEST_CR3 with L1's CR3 if EPT is disabled *and*
> >  	 * nested early checks are disabled.  In the event of a "late" VM-Fail,
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index a480804ae27a3..7c6e94e32100e 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -11562,6 +11562,7 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_inj_virq);
> >  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_page_fault);
> >  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_msr);
> >  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_cr);
> > +EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_nested_vmlaunch_resume);
> >  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_nested_vmrun);
> >  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_nested_vmexit);
> >  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_nested_vmexit_inject);
> > -- 
> > 2.26.2
> >