linux-kernel - Re: [PATCH 00/12] SEV Live Migration Patchset.

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Message-ID: <101d137c-724a-2b79-f865-e7af8135ca86@redhat.com>
Date:   Thu, 19 Mar 2020 14:05:21 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Ashish Kalra <ashish.kalra@....com>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Joerg Roedel <joro@...tes.org>, Borislav Petkov <bp@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        David Rientjes <rientjes@...gle.com>, X86 ML <x86@...nel.org>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH 00/12] SEV Live Migration Patchset.

On 17/02/20 20:49, Ashish Kalra wrote:
>> Also, you're making guest-side and host-side changes.  What ensures
>> that you don't try to migrate a guest that doesn't support the
>> hypercall for encryption state tracking?
> This is a good question and it is still an open-ended question. There
> are two possibilities here: guest does not have any unencrypted pages
> (for e.g booting 32-bit) and so it does not make any hypercalls, and 
> the other possibility is that the guest does not have support for
> the newer hypercall.
> 
> In the first case, all the guest pages are then assumed to be 
> encrypted and live migration happens as such.
> 
> For the second case, we have been discussing this internally,
> and one option is to extend the KVM capabilites/feature bits to check for this ?

You could extend the hypercall to completely block live migration (e.g.
a0=a1=~0, a2=0 to unblock or 1 to block).  The KVM_GET_PAGE_ENC_BITMAP
ioctl can also return the blocked/unblocked state.

Paolo