netdev - RE: [net-next 1/8] pci: Add flag indicating device has been assigned by KVM

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Date:	Fri, 23 Sep 2011 07:41:36 -0700
From:	"Rose, Gregory V" <gregory.v.rose@...el.com>
To:	Ian Campbell <ijc@...lion.org.uk>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"gospo@...hat.com" <gospo@...hat.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: RE: [net-next 1/8] pci: Add flag indicating device has been
 assigned by KVM

> -----Original Message-----
> From: Ian Campbell [mailto:ijc@...lion.org.uk]
> Sent: Friday, September 23, 2011 12:28 AM
> To: Kirsher, Jeffrey T
> Cc: davem@...emloft.net; konrad.wilk@...cle.com; Jesse Barnes; Rose,
> Gregory V; netdev@...r.kernel.org; gospo@...hat.com; linux-
> pci@...r.kernel.org
> Subject: Re: [net-next 1/8] pci: Add flag indicating device has been
> assigned by KVM
> 
> On Thu, 2011-09-22 at 21:16 -0700, Jeff Kirsher wrote:
> >
> >
> > Jesse/Konrad/Ian-
> >
> > I sent this patch out as part of a pull request for David Miller's
> > net-next tree.  I know that Greg sent this originally out to the
> > linux-pci mailing list as a RFC. Since Greg also has a patch against
> > ixgbe which implemented this flag, I sent both patches for inclusion
> > into David Miller's net-next.
> >
> > Dave is wanting to ensure that the PCI maintainers have reviewed this
> > and are ok with it before pulls my series of patches.
> 
> I'm not a PCI maintainer by any stretch of the imagination but FWIW this
> change is fine by me.
> 
> My original reason for commenting on this patch was just to wonder
> whether this would also be useful for Xen and I think the answer is we
> should patch xen-pciback to use this new flag but I've not had time to
> look into that.
> 
> I suppose by that measure the comment could be less KVM specific:
> > +       /* Provide indication device is assigned by KVM */
> > +       PCI_DEV_FLAGS_ASSIGNED = (__force pci_dev_flags_t) 4,

We can resubmit with a more generic comment, maybe this:

/* Provide indication device is assigned by a Virtual Machine Manager */

> 
> but that's not exactly a big deal.
> 
> I suppose really the flag indicates "VF in use" rather than necessarily
> "assigned"? Would it be just as bad to have a VF driver in the host
> active when the PF was unloaded?

There is no issue with unloading an active VF in the host because the hot remove event is seen by the host and accesses to the device stop.  However, when you hot remove the device the host and it is assigned to a VM the VM is unaware of the event and has no way of propagating the hot remove event.  So it really is a VF assigned to VM flag.  There's no need to mark VFs as in use in the host.

- Greg