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

[Dexuan Cui <decui@microsoft.com>]

> 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 = 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