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

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Message-ID: <m235xlfv9s.fsf@dme.org>
Date:   Wed, 24 Feb 2021 13:30:23 +0000
From:   David Edmondson <dme@....org>
To:     Jim Mattson <jmattson@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     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 Tuesday, 2021-02-23 at 15:13:54 -08, 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.

v3 now always shows the PDPTRs if they exist.

dme.
-- 
I've got a little black book with my poems in.