linux-kernel - Re: 3.6-rc7 boot crash + bisection

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Date:	Thu, 27 Sep 2012 18:22:49 +0200
From:	Florian Dazinger <florian@...inger.net>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	"Roedel, Joerg" <Joerg.Roedel@....com>,
	iommu <iommu@...ts.linux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: 3.6-rc7 boot crash + bisection

Am Wed, 26 Sep 2012 16:04:03 -0600
schrieb Alex Williamson <alex.williamson@...hat.com>:

> On Wed, 2012-09-26 at 13:50 -0600, Alex Williamson wrote:
> > On Wed, 2012-09-26 at 10:21 -0600, Alex Williamson wrote:
> > > On Wed, 2012-09-26 at 17:10 +0200, Roedel, Joerg wrote:
> > > > On Wed, Sep 26, 2012 at 08:35:59AM -0600, Alex Williamson wrote:
> > > > > Hmm, that throws a kink in iommu groups.  So perhaps we need to make an
> > > > > alias interface to iommu groups.  Seems like this could just be an extra
> > > > > parameter to iommu_group_get and iommu_group_add_device (empty in the
> > > > > typical case).  Then we have the problem of what's the type for an
> > > > > alias?  For AMI-Vi, it's a u16, but we need to be more generic than
> > > > > that.  Maybe iommu groups should just treat it as a void* so iommus can
> > > > > use a pointer to some structure or a fixed value like a u16 bus:slot.
> > > > > Thoughts?
> > > > 
> > > > Good question. The iommu-groups are part of the IOMMU-API, with an
> > > > interface to the IOMMU drivers and one to the users of IOMMU-API. So the
> > > > alias handling itself should be a function of the interface to the IOMMU
> > > > driver. In general the interface should not be bus specific.
> > > > 
> > > > So a void pointer seems the only logical choice then. But I would not
> > > > limit its scope to alias handling. How about making it a bus-private
> > > > pointer where IOMMU driver store bus-specific information. That way we
> > > > make sure that there is one struct per bus-type for this pointer, and
> > > > not one structure per IOMMU driver.
> > > 
> > > I thought of another approach that may actually be more 3.6 worthy.
> > > What if we just make the iommu driver handle it?  For instance,
> > > amd_iommu can walk the alias table looking for entries that use the same
> > > alias and get the device via pci_get_bus_and_slot.  If it finds a device
> > > with an iommu group, it attaches the new device to the same group,
> > > hiding anything about aliases from the group layer.  It just groups all
> > > devices within the range.  I think the only complication is making sure
> > > we're safe around device hotplug while we're doing this.  Thanks,
> > 
> > I think this could work.  Instead of searching for other devices, check
> > for or allocate an iommu group on the alias dev_data, any "virtual"
> > aliases use that iommu group.  Florian, could you test this as well?
> 
> Here's a lockdep clean version of it:
> 
> amd_iommu: Handle aliases not backed by devices
> 
[ skipped patch ]

yes, this patch is working for me, too. I also tested your second patch, it was working as well.
thanks, Florian
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