linux-kernel - Re: [PATCH v8 18/18] KVM: SVM: Enable SEV live migration feature implicitly on Incoming VM(s).

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Message-ID: <20201204214656.GC1424@ashkalra_ubuntu_server>
Date:   Fri, 4 Dec 2020 21:46:56 +0000
From:   Ashish Kalra <ashish.kalra@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        joro@...tes.org, bp@...e.de, Thomas.Lendacky@....com,
        x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        srutherford@...gle.com, rientjes@...gle.com,
        venu.busireddy@...cle.com, brijesh.singh@....com
Subject: Re: [PATCH v8 18/18] KVM: SVM: Enable SEV live migration feature
 implicitly on Incoming VM(s).

Hello Paolo,

On Fri, Dec 04, 2020 at 12:22:48PM +0100, Paolo Bonzini wrote:
> On 05/05/20 23:22, Ashish Kalra wrote:
> > From: Ashish Kalra <ashish.kalra@....com>
> > 
> > For source VM, live migration feature is enabled explicitly
> > when the guest is booting, for the incoming VM(s) it is implied.
> > This is required for handling A->B->C->... VM migrations case.
> > 
> > Signed-off-by: Ashish Kalra <ashish.kalra@....com>
> > ---
> >   arch/x86/kvm/svm/sev.c | 7 +++++++
> >   1 file changed, 7 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> > index 6f69c3a47583..ba7c0ebfa1f3 100644
> > --- a/arch/x86/kvm/svm/sev.c
> > +++ b/arch/x86/kvm/svm/sev.c
> > @@ -1592,6 +1592,13 @@ int svm_set_page_enc_bitmap(struct kvm *kvm,
> >   	if (ret)
> >   		goto unlock;
> > +	/*
> > +	 * For source VM, live migration feature is enabled
> > +	 * explicitly when the guest is booting, for the
> > +	 * incoming VM(s) it is implied.
> > +	 */
> > +	sev_update_migration_flags(kvm, KVM_SEV_LIVE_MIGRATION_ENABLED);
> > +
> >   	bitmap_copy(sev->page_enc_bmap + BIT_WORD(gfn_start), bitmap,
> >   		    (gfn_end - gfn_start));
> > 
> 
> I would prefer that userspace does this using KVM_SET_MSR instead.
> 
> 

Ok.

But, this is for a VM which has already been migrated based on feature
support on host and guest and host negotation and enablement of the live
migration support, so i am assuming that a VM which has already been
migrated can have this support enabled implicitly for further migration.

Thanks,
Ashish