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

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Message-ID: <43F901BD926A4E43B106BF17856F0755019414D59C@orsmsx508.amr.corp.intel.com>
Date:	Thu, 28 Jul 2011 09:42:24 -0700
From:	"Rose, Gregory V" <gregory.v.rose@...el.com>
To:	Ian Campbell <ijc@...lion.org.uk>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"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 9:28 AM
> To: Rose, Gregory V
> Cc: Konrad Rzeszutek Wilk; 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 Thu, 2011-07-28 at 08:58 -0700, Rose, Gregory V wrote:
> > > -----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.
> 
> my mistake -- under Xen the iommu is driver by the hypervisor and not
> the domain 0 kernel so there is no iommu_* in pciback.
> 
> >   It took me a week of digging around in the KVM module code just to
> > find these hooks.
> 
> I'm not actually sure where in pciback the right place to put this would
> be is, perhaps Konrad has an idea.

OK, but I hope Xen can still use the dev_flag assignment bit.

Thanks,

- Greg