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From:   Haiyang Zhang <haiyangz@microsoft.com>
To:     Leon Romanovsky <leon@kernel.org>, Dexuan Cui <decui@microsoft.com>
CC:     "davem@davemloft.net" <davem@davemloft.net>,
        "kuba@kernel.org" <kuba@kernel.org>,
        KY Srinivasan <kys@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
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        Wei Liu <liuwe@microsoft.com>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>
Subject: RE: [PATCH net-next] net: mana: Add a driver for Microsoft Azure
 Network Adapter (MANA)
Thread-Topic: [PATCH net-next] net: mana: Add a driver for Microsoft Azure
 Network Adapter (MANA)
Thread-Index: AQHXKzvmwFT+jLn9hE+ope3TVVs2GqqotGEAgAAIZ4CAAEYnAIAAHRmw
Date:   Wed, 7 Apr 2021 14:41:45 +0000
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> -----Original Message-----
> From: Leon Romanovsky <leon@kernel.org>
> Sent: Wednesday, April 7, 2021 8:51 AM
> To: Dexuan Cui <decui@microsoft.com>
> Cc: davem@davemloft.net; kuba@kernel.org; KY Srinivasan
> <kys@microsoft.com>; Haiyang Zhang <haiyangz@microsoft.com>; Stephen
> Hemminger <sthemmin@microsoft.com>; wei.liu@kernel.org; Wei Liu
> <liuwe@microsoft.com>; netdev@vger.kernel.org; linux-
> kernel@vger.kernel.org; linux-hyperv@vger.kernel.org
> Subject: Re: [PATCH net-next] net: mana: Add a driver for Microsoft Azure
> Network Adapter (MANA)
>=20
> On Wed, Apr 07, 2021 at 08:40:13AM +0000, Dexuan Cui wrote:
> > > From: Leon Romanovsky <leon@kernel.org>
> > > Sent: Wednesday, April 7, 2021 1:10 AM
> > >
> > > <...>
> > >
> > > > +int gdma_verify_vf_version(struct pci_dev *pdev)
> > > > +{
> > > > +	struct gdma_context *gc =3D pci_get_drvdata(pdev);
> > > > +	struct gdma_verify_ver_req req =3D { 0 };
> > > > +	struct gdma_verify_ver_resp resp =3D { 0 };
> > > > +	int err;
> > > > +
> > > > +	gdma_init_req_hdr(&req.hdr, GDMA_VERIFY_VF_DRIVER_VERSION,
> > > > +			  sizeof(req), sizeof(resp));
> > > > +
> > > > +	req.protocol_ver_min =3D GDMA_PROTOCOL_FIRST;
> > > > +	req.protocol_ver_max =3D GDMA_PROTOCOL_LAST;
> > > > +
> > > > +	err =3D gdma_send_request(gc, sizeof(req), &req, sizeof(resp), &r=
esp);
> > > > +	if (err || resp.hdr.status) {
> > > > +		pr_err("VfVerifyVersionOutput: %d, status=3D0x%x\n", err,
> > > > +		       resp.hdr.status);
> > > > +		return -EPROTO;
> > > > +	}
> > > > +
> > > > +	return 0;
> > > > +}
> > >
> > > <...>
> > > > +	err =3D gdma_verify_vf_version(pdev);
> > > > +	if (err)
> > > > +		goto remove_irq;
> > >
> > > Will this VF driver be used in the guest VM? What will prevent from u=
sers
> to
> > > change it?
> > > I think that such version negotiation scheme is not allowed.
> >
> > Yes, the VF driver is expected to run in a Linux VM that runs on Azure.
> >
> > Currently gdma_verify_vf_version() just tells the PF driver that the VF
> driver
> > is only able to support GDMA_PROTOCOL_V1, and want to use
> > GDMA_PROTOCOL_V1's message formats to talk to the PF driver later.
> >
> > enum {
> >         GDMA_PROTOCOL_UNDEFINED =3D 0,
> >         GDMA_PROTOCOL_V1 =3D 1,
> >         GDMA_PROTOCOL_FIRST =3D GDMA_PROTOCOL_V1,
> >         GDMA_PROTOCOL_LAST =3D GDMA_PROTOCOL_V1,
> >         GDMA_PROTOCOL_VALUE_MAX
> > };
> >
> > The PF driver is supposed to always support GDMA_PROTOCOL_V1, so I
> expect
> > here gdma_verify_vf_version() should succeed. If a user changes the Lin=
ux
> VF
> > driver and try to use a protocol version not supported by the PF driver=
,
> then
> > gdma_verify_vf_version() will fail; later, if the VF driver tries to ta=
lk to the
> PF
> > driver using an unsupported message format, the PF driver will return a
> failure.
>=20
> The worry is not for the current code, but for the future one when you wi=
ll
> support v2, v3 e.t.c. First, your code will look like a spaghetti and
> second, users will try and mix vX with "unsupported" commands just for th=
e
> fun.

In the future, if the protocol version updated on the host side, guests nee=
d=20
to support different host versions because not all hosts are updated=20
(simultaneously). So this negotiation is necessary to know the supported=20
version, and decide the proper command version to use.=20

If any user try "unsupported commands just for the fun", the host will deny=
=20
and return an error.

Thanks,
- Haiyang