netdev - RE: [RFC net-next PATCH 1/4] pci: Add flag indicating device has been assigned by KVM

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Message-ID: <43F901BD926A4E43B106BF17856F0755019414D525@orsmsx508.amr.corp.intel.com>
Date:	Thu, 28 Jul 2011 08:58:03 -0700
From:	"Rose, Gregory V" <gregory.v.rose@...el.com>
To:	Ian Campbell <ijc@...lion.org.uk>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"bhutchings@...arflare.com" <bhutchings@...arflare.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: RE: [RFC net-next PATCH 1/4] pci: Add flag indicating device has
 been assigned by KVM

> -----Original Message-----
> From: Ian Campbell [mailto:ijc@...lion.org.uk]
> Sent: Thursday, July 28, 2011 8:11 AM
> To: Rose, Gregory V; Konrad Rzeszutek Wilk
> Cc: netdev@...r.kernel.org; davem@...emloft.net;
> bhutchings@...arflare.com; Kirsher, Jeffrey T; Jesse Barnes; linux-
> pci@...r.kernel.org
> Subject: Re: [RFC net-next PATCH 1/4] pci: Add flag indicating device has
> been assigned by KVM
> 
> On Wed, 2011-07-27 at 15:17 -0700, Greg Rose wrote:
> > Device drivers that create and destroy SR-IOV virtual functions via
> > calls to pci_enable_sriov() and pci_disable_sriov can cause catastrophic
> > failures if they attempt to destroy VFs while they are assigned to
> > guest virtual machines.  By adding a flag for use by the KVM module
> > to indicate that a device is assigned a device driver can check that
> > flag and avoid destroying VFs while they are assigned and avoid system
> > failures.
> >
> > Signed-off-by: Greg Rose <gregory.v.rose@...el.com>
> > ---
> >
> >  include/linux/pci.h     |    2 ++
> 
> I added Jesse and linux-pci to CC.
> 
> >  virt/kvm/assigned-dev.c |    2 ++
> >  virt/kvm/iommu.c        |    4 ++++
> >  3 files changed, 8 insertions(+), 0 deletions(-)
> 
> I suppose this would also be useful in Xen's pciback or any other system
> which does passthrough? (Konrad CC'd for pciback)

Definitely yes.  Xen experiences the same issues when the PF driver is removed while VFs are assigned to guests.

> 
> Is there some common lower layer we could hook this in to? (does
> iommu_attach/detach_device make sense?) Or shall we just add the flag
> manipulations to pciback as well?
[Greg Rose] 

I was unaware of any common lower layers, i.e I didn't know that Xen also uses the iommu_attach/detach_device calls.  It took me a week of digging around in the KVM module code just to find these hooks.  Generally I stick to Ethernet device drivers and I'm not that familiar with device pass through code.  I was just confronted with a problem and looking for some way to fix it.

;^)

That sounds like a good idea, let me have a look at it.

- Greg