linux-kernel - Re: [PATCH 5/6] vdpa: introduce virtio pci driver

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Date:   Mon, 8 Jun 2020 05:31:48 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        rob.miller@...adcom.com, lingshan.zhu@...el.com,
        eperezma@...hat.com, lulu@...hat.com, shahafs@...lanox.com,
        hanand@...inx.com, mhabets@...arflare.com, gdawar@...inx.com,
        saugatm@...inx.com, vmireyno@...vell.com,
        zhangweining@...jie.com.cn, eli@...lanox.com
Subject: Re: [PATCH 5/6] vdpa: introduce virtio pci driver

On Mon, Jun 08, 2020 at 05:18:44PM +0800, Jason Wang wrote:
> 
> On 2020/6/8 下午2:32, Michael S. Tsirkin wrote:
> > On Mon, Jun 08, 2020 at 11:32:31AM +0800, Jason Wang wrote:
> > > On 2020/6/7 下午9:51, Michael S. Tsirkin wrote:
> > > > On Fri, Jun 05, 2020 at 04:54:17PM +0800, Jason Wang wrote:
> > > > > On 2020/6/2 下午3:08, Jason Wang wrote:
> > > > > > > > +static const struct pci_device_id vp_vdpa_id_table[] = {
> > > > > > > > +    { PCI_DEVICE(PCI_VENDOR_ID_REDHAT_QUMRANET, PCI_ANY_ID) },
> > > > > > > > +    { 0 }
> > > > > > > > +};
> > > > > > > This looks like it'll create a mess with either virtio pci
> > > > > > > or vdpa being loaded at random. Maybe just don't specify
> > > > > > > any IDs for now. Down the road we could get a
> > > > > > > distinct vendor ID or a range of device IDs for this.
> > > > > > Right, will do.
> > > > > > 
> > > > > > Thanks
> > > > > Rethink about this. If we don't specify any ID, the binding won't work.
> > > > We can bind manually. It's not really for production anyway, so
> > > > not a big deal imho.
> > > 
> > > I think you mean doing it via "new_id", right.
> > I really meant driver_override. This is what people have been using
> > with pci-stub for years now.
> 
> 
> Do you want me to implement "driver_overrid" in this series, or a NULL
> id_table is sufficient?


Doesn't the pci subsystem create driver_override for all devices
on the pci bus?

> 
> > 
> > > > > How about using a dedicated subsystem vendor id for this?
> > > > > 
> > > > > Thanks
> > > > If virtio vendor id is used then standard driver is expected
> > > > to bind, right? Maybe use a dedicated vendor id?
> > > 
> > > I meant something like:
> > > 
> > > static const struct pci_device_id vp_vdpa_id_table[] = {
> > >      { PCI_DEVICE_SUB(PCI_VENDOR_ID_REDHAT_QUMRANET, PCI_ANY_ID,
> > > VP_TEST_VENDOR_ID, VP_TEST_DEVICE_ID) },
> > >      { 0 }
> > > };
> > > 
> > > Thanks
> > > 
> > Then regular virtio will still bind to it. It has
> > 
> > drivers/virtio/virtio_pci_common.c:     { PCI_DEVICE(PCI_VENDOR_ID_REDHAT_QUMRANET, PCI_ANY_ID) },
> > 
> > 
> 
> IFCVF use this to avoid the binding to regular virtio device.


Ow. Indeed:

#define IFCVF_VENDOR_ID         0x1AF4

Which is of course not an IFCVF vendor id, it's the Red Hat vendor ID.

I missed that.

Does it actually work if you bind a virtio driver to it?
I'm guessing no otherwise they wouldn't need IFC driver, right?




> Looking at
> pci_match_one_device() it checks both subvendor and subdevice there.
> 
> Thanks


But IIUC there is no guarantee that driver with a specific subvendor
matches in presence of a generic one.
So either IFC or virtio pci can win, whichever binds first.

I guess we need to blacklist IFC in virtio pci probe code. Ugh.

-- 
MST