linux-kernel - Re: [PATCH v2 1/3] KVM: x86: dump_vmcs should not assume GUEST_IA32

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Message-ID: <YDWSxqOODX4RYTeP@google.com>
Date:   Tue, 23 Feb 2021 15:41:58 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     David Edmondson <david.edmondson@...cle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Joerg Roedel <joro@...tes.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        kvm list <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH v2 1/3] KVM: x86: dump_vmcs should not assume
 GUEST_IA32_EFER is valid

On Tue, Feb 23, 2021, Jim Mattson wrote:
> On Tue, Feb 23, 2021 at 2:51 PM Sean Christopherson <seanjc@...gle.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.

I'm a-ok with that approach.