Re: [PATCH v2 1/2] KVM: nested/x86: update trace_kvm_nested_vmrun() to suppot VMX

Sean Christopherson
2022-08-03T16:50:17Z

If we want to add a unique identifier for nested x86, use "KVM: x86/nested:" to
align with the MMU and to make `grep "KVM: x86"` viable. Ideally, we'd align with
nVMX and nSVM, but nx86 is pretty gross and looks like a typo.

I have a slight preference for using a plain "KVM: x86:", as I suspect we'll never
have enough common nested to make it worth differentiating, but I've no objection
if you want to go with "KVM: x86/nested:".

On Mon, Jul 18, 2022, Mingwei Zhang wrote:
> Update trace_kvm_nested_vmrun() to support VMX by adding a new field 'isa';
> update the output to print out VMX/SVM related naming respectively,
> eg., vmcb vs. vmcs; npt vs. ept.
>
> In addition, print nested EPT/NPT address instead of the 1bit of nested
> ept/npt on/off. This should convey more information in the trace. When
> nested ept/npt is not used, simply print "0x0" so that we don't lose any
> information.

Adding a new field that's not related to the VMX vs. SVM change belongs in a
separate patch.

> Opportunistically update the call site of trace_kvm_nested_vmrun() to make
> one line per parameter.
>
> Signed-off-by: Mingwei Zhang <mizhang@google.com>
> ---
> arch/x86/kvm/svm/nested.c | 7 +++++--
> arch/x86/kvm/trace.h | 29 ++++++++++++++++++++---------
> 2 files changed, 25 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index ba7cd26f438f..8581164b6808 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -724,11 +724,14 @@ int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb12_gpa,
> struct vcpu_svm *svm = to_svm(vcpu);
> int ret;
>
> - trace_kvm_nested_vmrun(svm->vmcb->save.rip, vmcb12_gpa,
> + trace_kvm_nested_vmrun(svm->vmcb->save.rip,
> + vmcb12_gpa,
> vmcb12->save.rip,
> vmcb12->control.int_ctl,
> vmcb12->control.event_inj,
> - vmcb12->control.nested_ctl);
> + vmcb12->control.nested_ctl,
> + vmcb12->control.nested_cr3,
> + KVM_ISA_SVM);
>
> trace_kvm_nested_intercepts(vmcb12->control.intercepts[INTERCEPT_CR] & 0xffff,
> vmcb12->control.intercepts[INTERCEPT_CR] >> 16,
> diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
> index de4762517569..aac4c8bd2c3a 100644
> --- a/arch/x86/kvm/trace.h
> +++ b/arch/x86/kvm/trace.h
> @@ -580,8 +580,10 @@ TRACE_EVENT(kvm_pv_eoi,
> */
> TRACE_EVENT(kvm_nested_vmrun,

I think it makes sense to rename this to kvm_nested_vmenter. VMRUN is SVM-only,
and tracepoints aren't ABI.

> TP_PROTO(__u64 rip, __u64 vmcb, __u64 nested_rip, __u32 int_ctl,
> - __u32 event_inj, bool npt),
> - TP_ARGS(rip, vmcb, nested_rip, int_ctl, event_inj, npt),
> + __u32 event_inj, bool npt_enabled, __u64 npt_addr,
> + __u32 isa),
> + TP_ARGS(rip, vmcb, nested_rip, int_ctl, event_inj, npt_enabled,
> + npt_addr, isa),
>
> TP_STRUCT__entry(
> __field( __u64, rip )
> @@ -589,7 +591,9 @@ TRACE_EVENT(kvm_nested_vmrun,
> __field( __u64, nested_rip )
> __field( __u32, int_ctl )
> __field( __u32, event_inj )
> - __field( bool, npt )
> + __field( bool, npt_enabled )

s/npt_enabled/tdp_enabled, or maybe ntdp_enabled?

> + __field( __u64, npt_addr )

Hmm, either

s/npt_addr/nested_pgd

or

s/npt_addr/guest_pgd

"npt_addr" or "tdp_addr" is too ambiguous, e.g. it can be interpreted as the address
of a TDP page fault.

My vote would be for "guest_pgd" and then pass in the non-nested CR3 when L1 isn't
using nTDP.

> + __field( __u32, isa )
> ),
>
> TP_fast_assign(
> @@ -598,14 +602,21 @@ TRACE_EVENT(kvm_nested_vmrun,
> __entry->nested_rip = nested_rip;
> __entry->int_ctl = int_ctl;
> __entry->event_inj = event_inj;
> - __entry->npt = npt;
> + __entry->npt_enabled = npt_enabled;
> + __entry->npt_addr = npt_addr;
> + __entry->isa = isa;
> ),
>
> - TP_printk("rip: 0x%016llx vmcb: 0x%016llx nrip: 0x%016llx int_ctl: 0x%08x "
> - "event_inj: 0x%08x npt: %s",
> - __entry->rip, __entry->vmcb, __entry->nested_rip,
> - __entry->int_ctl, __entry->event_inj,
> - __entry->npt ? "on" : "off")
> + TP_printk("rip: 0x%016llx %s: 0x%016llx nested rip: 0x%016llx "
> + "int_ctl: 0x%08x event_inj: 0x%08x nested %s: 0x%016llx",

This needs to explicitly print "nTDP on/off". As proposed, "nested ept/npt: %addr"
doesn't capture that. (a) addr=0 is perfectly legal, and (b) addr!=0 is also legal
if nTDP isn't enabled, i.e. a non-zero nested_cr3/eptp is ignore by hardware

> + __entry->rip,
> + __entry->isa == KVM_ISA_VMX ? "vmcs" : "vmcb",
> + __entry->vmcb,
> + __entry->nested_rip,
> + __entry->int_ctl,
> + __entry->event_inj,
> + __entry->isa == KVM_ISA_VMX ? "ept" : "npt",
> + __entry->npt_enabled ? __entry->npt_addr : 0x0)
> );
>
> TRACE_EVENT(kvm_nested_intercepts,
> --
> 2.37.0.170.g444d1eabd0-goog
>