On Wed, Apr 07, 2021 at 08:40:13AM +0000, Dexuan Cui wrote:
> > From: Leon Romanovsky <leon@xxxxxxxxxx>
> > 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.
The worry is not for the current code, but for the future one when you will
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 the
fun.
Thanks
>
> Thanks,
> -- Dexuan
