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From:   Dexuan Cui <decui@microsoft.com>
To:     Leon Romanovsky <leon@kernel.org>
CC:     "davem@davemloft.net" <davem@davemloft.net>,
        "kuba@kernel.org" <kuba@kernel.org>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        Wei Liu <liuwe@microsoft.com>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "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: AQHXK4VsK9CYzM87fki9gwnmLmNhk6qotOdw
Date:   Wed, 7 Apr 2021 08:40:13 +0000
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References: <20210406232321.12104-1-decui@microsoft.com>
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> From: Leon Romanovsky <leon@kernel.org>
> Sent: Wednesday, April 7, 2021 1:10 AM
>=20
> <...>
>=20
> > +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), &resp)=
;
> > +	if (err || resp.hdr.status) {
> > +		pr_err("VfVerifyVersionOutput: %d, status=3D0x%x\n", err,
> > +		       resp.hdr.status);
> > +		return -EPROTO;
> > +	}
> > +
> > +	return 0;
> > +}
>=20
> <...>
> > +	err =3D gdma_verify_vf_version(pdev);
> > +	if (err)
> > +		goto remove_irq;
>=20
> Will this VF driver be used in the guest VM? What will prevent from users=
 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 dri=
ver
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 Linux V=
F
driver and try to use a protocol version not supported by the PF driver, th=
en
gdma_verify_vf_version() will fail; later, if the VF driver tries to talk t=
o the PF
driver using an unsupported message format, the PF driver will return a fai=
lure.

Thanks,
-- Dexuan