netdev - RE: [PATCH net-next] net: mana: Add a driver for Microsoft Azure Network Adapter (MANA)

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Message-ID: <MW2PR2101MB08923D4417E44C5750BFB964BF759@MW2PR2101MB0892.namprd21.prod.outlook.com>
Date:   Wed, 7 Apr 2021 08:40:13 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     Leon Romanovsky <leon@...nel.org>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        Wei Liu <liuwe@...rosoft.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>
Subject: RE: [PATCH net-next] net: mana: Add a driver for Microsoft Azure
 Network Adapter (MANA)

> From: Leon Romanovsky <leon@...nel.org>
> Sent: Wednesday, April 7, 2021 1:10 AM
> 
> <...>
> 
> > +int gdma_verify_vf_version(struct pci_dev *pdev)
> > +{
> > +	struct gdma_context *gc = pci_get_drvdata(pdev);
> > +	struct gdma_verify_ver_req req = { 0 };
> > +	struct gdma_verify_ver_resp resp = { 0 };
> > +	int err;
> > +
> > +	gdma_init_req_hdr(&req.hdr, GDMA_VERIFY_VF_DRIVER_VERSION,
> > +			  sizeof(req), sizeof(resp));
> > +
> > +	req.protocol_ver_min = GDMA_PROTOCOL_FIRST;
> > +	req.protocol_ver_max = GDMA_PROTOCOL_LAST;
> > +
> > +	err = gdma_send_request(gc, sizeof(req), &req, sizeof(resp), &resp);
> > +	if (err || resp.hdr.status) {
> > +		pr_err("VfVerifyVersionOutput: %d, status=0x%x\n", err,
> > +		       resp.hdr.status);
> > +		return -EPROTO;
> > +	}
> > +
> > +	return 0;
> > +}
> 
> <...>
> > +	err = gdma_verify_vf_version(pdev);
> > +	if (err)
> > +		goto remove_irq;
> 
> 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 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 = 0,
        GDMA_PROTOCOL_V1 = 1,
        GDMA_PROTOCOL_FIRST = GDMA_PROTOCOL_V1,
        GDMA_PROTOCOL_LAST = 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 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 talk to the PF
driver using an unsupported message format, the PF driver will return a failure.

Thanks,
-- Dexuan