Re: [PATCH v2 1/3] KVM: x86: dump_vmcs should not assume GUEST_IA32_EFER is valid

Jim Mattson
2021-02-23T23:19:12Z

On Tue, Feb 23, 2021 at 2:51 PM Sean Christopherson <seanjc@google.com> wrote:
>
> On Fri, Feb 19, 2021, David Edmondson wrote:
> > If the VM entry/exit controls for loading/saving MSR_EFER are either
> > not available (an older processor or explicitly disabled) or not
> > used (host and guest values are the same), reading GUEST_IA32_EFER
> > from the VMCS returns an inaccurate value.
> >
> > Because of this, in dump_vmcs() don't use GUEST_IA32_EFER to decide
> > whether to print the PDPTRs - do so if the EPT is in use and CR4.PAE
> > is set.
>
> This isn't necessarily correct either. In a way, it's less correct as PDPTRs
> are more likely to be printed when they shouldn't, assuming most guests are
> 64-bit guests. It's annoying to calculate the effective guest EFER, but so
> awful that it's worth risking confusion over PDTPRs.

I still prefer a dump_vmcs that always dumps every VMCS field. But if
you really want to skip printing the PDPTEs when they're irrelevant,
can't you just use the "IA-32e mode guest" VM-entry control as a proxy
for EFER.LMA?