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

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Message-ID: <1316790220.23371.105.camel@zakaz.uk.xensource.com>
Date:	Fri, 23 Sep 2011 16:03:33 +0100
From:	Ian Campbell <ijc@...lion.org.uk>
To:	"Rose, Gregory V" <gregory.v.rose@...el.com>
Cc:	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"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

On Fri, 2011-09-23 at 07:41 -0700, Rose, Gregory V wrote:
> > -----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 */

Sounds good to me.
> 
> > 
> > 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.

Ah, ok. Thanks for explaining.

Ian.

-- 
Ian Campbell
Current Noise: High On Fire - Blessed Black Wings

Famous, adj.:
	Conspicuously miserable.
		-- Ambrose Bierce, "The Devil's Dictionary"

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