linux-kernel - Re: [virtio-dev] [PATCH] virtio

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Date:   Wed, 30 May 2018 20:15:43 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     "Duyck, Alexander H" <alexander.h.duyck@...el.com>
Cc:     "alexander.duyck@...il.com" <alexander.duyck@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "virtio-dev@...ts.oasis-open.org" <virtio-dev@...ts.oasis-open.org>,
        "Rustad, Mark D" <mark.d.rustad@...el.com>,
        "Daly, Dan" <dan.daly@...el.com>,
        "Bie, Tiwei" <tiwei.bie@...el.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "Liang, Cunming" <cunming.liang@...el.com>,
        "Wang, Zhihong" <zhihong.wang@...el.com>
Subject: Re: [virtio-dev] [PATCH] virtio_pci: support enabling VFs

On Wed, May 30, 2018 at 04:26:30PM +0000, Duyck, Alexander H wrote:
> On Wed, 2018-05-30 at 19:22 +0300, Michael S. Tsirkin wrote:
> > On Wed, May 30, 2018 at 09:10:57AM -0700, Alexander Duyck wrote:
> > > On Wed, May 30, 2018 at 1:55 AM, Tiwei Bie <tiwei.bie@...el.com> wrote:
> > > > There is a new feature bit allocated in virtio spec to
> > > > support SR-IOV (Single Root I/O Virtualization):
> > > > 
> > > > https://github.com/oasis-tcs/virtio-spec/issues/11
> > > > 
> > > > This patch enables the support for this feature bit in
> > > > virtio driver.
> > > > 
> > > > Signed-off-by: Tiwei Bie <tiwei.bie@...el.com>
> > > 
> > > So from a quick glance it looks like we are leaving SR-IOV enabled if
> > > the driver is removed. Do we want to have that behavior or should we
> > > be adding the code to disable SR-IOV and free the VFs on driver
> > > removal?
> > 
> > Could pci core handle it for us somehow?
> 
> Maybe, but it would require changes to the pci core to do it.
> 
> The problem is some drivers want to leave the VFs there since the PF
> doesn't really do anything, or they have the option of essentially
> putting the VFs into a standby state when the PF is gone.
> 
> My main concern is do we care if VFs are allocated and then somebody
> removes the driver and binds a different driver to the interface? If
> not then this code and be left as is, but I just wanted to be certain
> since I know this isn't just enabling SR-IOV we are having to do a
> number of other checks against the virtio device.

Well the spec says features have to be negotiated, and since we reset
the device when we unbind from it I think it's a given we should keep a
driver bound to the PF.

IOW until we are sure we need the capability to keep it enabled, let's
disable it to be safe.

-- 
MST