linux-kernel - Re: [RFC PATCH 3/6] KVM: SVM: Implement demand page pinning

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Message-ID: <CAMkAt6rCU3K-dk7edxa9iKrOZ0uh5442K0U5Fbux=js0q6qQ+g@mail.gmail.com>
Date:   Tue, 25 Jan 2022 10:59:39 -0700
From:   Peter Gonda <pgonda@...gle.com>
To:     "Nikunj A. Dadhania" <nikunj@....com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Bharata B Rao <bharata@....com>
Subject: Re: [RFC PATCH 3/6] KVM: SVM: Implement demand page pinning

On Tue, Jan 25, 2022 at 10:49 AM Nikunj A. Dadhania <nikunj@....com> wrote:
>
> Hi Peter
>
> On 1/25/2022 10:17 PM, Peter Gonda wrote:
> >> @@ -1637,8 +1627,6 @@ static void sev_migrate_from(struct kvm_sev_info *dst,
> >>         src->handle = 0;
> >>         src->pages_locked = 0;
> >>         src->enc_context_owner = NULL;
> >> -
> >> -       list_cut_before(&dst->regions_list, &src->regions_list, &src->regions_list);
> > I think we need to move the pinned SPTE entries into the target, and
> > repin the pages in the target here. Otherwise the pages will be
> > unpinned when the source is cleaned up. Have you thought about how
> > this could be done?
> >
> I am testing migration with pinned_list, I see that all the guest pages are
> transferred/pinned on the other side during migration. I think that there is
> assumption that all private pages needs to be moved.
>
> QEMU: target/i386/sev.c:bool sev_is_gfn_in_unshared_region(unsigned long gfn)
>
> Will dig more on this.

The code you linked appears to be for a remote migration. This
function is for an "intra-host" migration meaning we are just moving
the VMs memory and state to a new userspace VMM on the same not an
entirely new host.

>
> Regards
> Nikunj