Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Tue, 22 Feb 2022 12:29:39 -0700
From:   Alex Williamson <alex.williamson@redhat.com>
To:     Jason Gunthorpe <jgg@nvidia.com>
Cc:     Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-crypto@vger.kernel.org, cohuck@redhat.com,
        mgurtovoy@nvidia.com, yishaih@nvidia.com, linuxarm@huawei.com,
        liulongfang@huawei.com, prime.zeng@hisilicon.com,
        jonathan.cameron@huawei.com, wangzhou1@hisilicon.com
Subject: Re: [PATCH v5 0/8] vfio/hisilicon: add ACC live migration driver
Message-ID: <20220222122939.0394d152.alex.williamson@redhat.com>
In-Reply-To: <20220222004943.GF193956@nvidia.com>
References: <20220221114043.2030-1-shameerali.kolothum.thodi@huawei.com>
        <20220222004943.GF193956@nvidia.com>
Organization: Red Hat
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Mon, 21 Feb 2022 20:49:43 -0400
Jason Gunthorpe <jgg@nvidia.com> wrote:

> On Mon, Feb 21, 2022 at 11:40:35AM +0000, Shameer Kolothum wrote:
> >=20
> > Hi,
> >=20
> > This series attempts to add vfio live migration support for
> > HiSilicon ACC VF devices based on the new v2 migration protocol
> > definition and mlx5 v8 series discussed here[0].
> >=20
> > RFCv4 --> v5
> >   - Dropped RFC tag as v2 migration APIs are more stable now.
> >   - Addressed review comments from Jason and Alex (Thanks!).
> >=20
> > This is sanity tested on a HiSilicon platform using the Qemu branch
> > provided here[1].
> >=20
> > Please take a look and let me know your feedback.
> >=20
> > Thanks,
> > Shameer
> > [0] https://lore.kernel.org/kvm/20220220095716.153757-1-yishaih@nvidia.=
com/
> > [1] https://github.com/jgunthorpe/qemu/commits/vfio_migration_v2
> >=20
> >=20
> > v3 --> RFCv4
> > -Based on migration v2 protocol and mlx5 v7 series.
> > -Added RFC tag again as migration v2 protocol is still under discussion.
> > -Added new patch #6 to retrieve the PF QM data.
> > -PRE_COPY compatibility check is now done after the migration data
> > =C2=A0transfer. This is not ideal and needs discussion. =20
>=20
> Alex, do you want to keep the PRE_COPY in just for acc for now? Or do
> you think this is not a good temporary use for it?
>=20
> We have some work toward doing the compatability more generally, but I
> think it will be a while before that is all settled.

In the original migration protocol I recall that we discussed that
using the pre-copy phase for compatibility testing, even without
additional device data, as a valid use case.  The migration driver of
course needs to account for the fact that userspace is not required to
perform a pre-copy, and therefore cannot rely on that exclusively for
compatibility testing, but failing a migration earlier due to detection
of an incompatibility is generally a good thing.

If the ACC driver wants to re-incorporate this behavior into a non-RFC
proposed series and we could align accepting them into the same kernel
release, that sounds ok to me.  Thanks,

Alex