linux-kernel - Re: [PATCH v4 3/3] KVM: x86: Print guest pgd in kvm_nested

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Date:   Tue, 30 Aug 2022 21:29:48 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Mingwei Zhang <mizhang@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH v4 3/3] KVM: x86: Print guest pgd in kvm_nested_vmenter()

On Thu, Aug 25, 2022, Mingwei Zhang wrote:
> ---
> diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
> index e7f0da9474f0..b2be0348bb14 100644
> --- a/arch/x86/kvm/trace.h
> +++ b/arch/x86/kvm/trace.h
> @@ -591,9 +591,10 @@ TRACE_EVENT(kvm_pv_eoi,
>   */
>  TRACE_EVENT(kvm_nested_vmenter,
>  	    TP_PROTO(__u64 rip, __u64 vmcb, __u64 nested_rip, __u32 int_ctl,
> -		     __u32 event_inj, bool tdp_enabled, __u32 isa),
> +		     __u32 event_inj, bool tdp_enabled, __u64 guest_tdp,

s/guest_tdp_pgd to differentiate it from "tdp_enabled"


>         TP_printk("rip: 0x%016llx %s: 0x%016llx nested_rip: 0x%016llx "
> -                 "int_ctl: 0x%08x event_inj: 0x%08x nested_%s: %s",
> +                 "int_ctl: 0x%08x event_inj: 0x%08x nested_%s: %s, "
> +                 "guest_pgd: 0x%016llx",

It's a little gross, but this can spit out nested_eptp vs. nested_cr3 vs. guest_cr3.

>                 __entry->rip,
>                 __entry->isa == KVM_ISA_VMX ? "vmcs" : "vmcb",
>                 __entry->vmcb,

> @@ -624,7 +628,8 @@ TRACE_EVENT(kvm_nested_vmenter,
>  		__entry->int_ctl,
>  		__entry->event_inj,
>  		__entry->isa == KVM_ISA_VMX ? "ept" : "npt",
> -		__entry->tdp_enabled ? "on" : "off")
> +		__entry->tdp_enabled ? "on" : "off",

To keep things aligned, and because "on nested_eptp" reads as a combined
snippet

  event_inj: 0x00000000 nested_ept: off guest_cr3: 0x0000000001007000
  event_inj: 0x00000000 nested_ept: off guest_cr3: 0x0000000001007000
  event_inj: 0x00000000 nested_ept: on nested_eptp: 0x0000000007ec501e
  event_inj: 0x00000000 nested_ept: on nested_eptp: 0x0000000007ec501e

what about teaking the format so that the output looks like this?

  event_inj: 0x00000000 nested_ept=n guest_cr3: 0x0000000001007000
  event_inj: 0x00000000 nested_ept=n guest_cr3: 0x0000000001007000
  event_inj: 0x00000000 nested_ept=y nested_eptp: 0x0000000007ec501e
  event_inj: 0x00000000 nested_ept=y nested_eptp: 0x0000000007ec501e

Deviating from the ": " style bothers me, but I find this difficult to read.
Again, letters delimited by whitespace get visually clumped together.

  event_inj: 0x00000000 nested_ept: n guest_cr3: 0x0000000001007000
  event_inj: 0x00000000 nested_ept: n guest_cr3: 0x0000000001007000
  event_inj: 0x00000000 nested_ept: y nested_eptp: 0x0000000007ec501e
  event_inj: 0x00000000 nested_ept: y nested_eptp: 0x0000000007ec501e

And this looks like a typo

  event_inj: 0x00000000 nested_ept:n guest_cr3: 0x0000000001007000
  event_inj: 0x00000000 nested_ept:n guest_cr3: 0x0000000001007000
  event_inj: 0x00000000 nested_ept:y nested_eptp: 0x0000000007ec501e
  event_inj: 0x00000000 nested_ept:y nested_eptp: 0x0000000007ec501e

We could leave off the nested_{ept/npt} entirely and leave the differentation to
the nested_eptp vs. nested_cr3 vs. guest_cr3, but I don't think that's worth
shaving a few chars.