linux-kernel - Re: [PATCH v3 0/9] KVM: Support guest MAXPHYADDR

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Message-ID: <CALMp9eQXHGnXo4ACX2-qYww4XdRODMn-O6CAvhupib67Li9S2w@mail.gmail.com>
Date:   Fri, 10 Jul 2020 10:13:07 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Mohammed Gamal <mgamal@...hat.com>, kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH v3 0/9] KVM: Support guest MAXPHYADDR < host MAXPHYADDR

On Fri, Jul 10, 2020 at 10:06 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 10/07/20 18:30, Jim Mattson wrote:
> >>
> >> This can be problem when having a mixed setup of machines with 5-level page
> >> tables and machines with 4-level page tables, as live migration can change
> >> MAXPHYADDR while the guest runs, which can theoretically introduce bugs.
> >
> > Huh? Changing MAXPHYADDR while the guest runs should be illegal. Or
> > have I missed some peculiarity of LA57 that makes MAXPHYADDR a dynamic
> > CPUID information field?
>
> Changing _host_ MAXPHYADDR while the guest runs, such as if you migrate
> from a host-maxphyaddr==46 to a host-maxphyaddr==52 machine (while
> keeping guest-maxphyaddr==46).

Ah, but what does that have to do with LA57?