Re: [RFC][Intel-IOMMU] Fix for IOMMU early crash

[Muli Ben-Yehuda <muli@il.ibm.com>]

On Mon, Sep 10, 2007 at 08:43:59AM -0700, Keshavamurthy, Anil S wrote:
> On Sun, Sep 09, 2007 at 02:16:19PM +0300, Muli Ben-Yehuda wrote:
> > On Sat, Sep 08, 2007 at 01:05:24PM -0700, Keshavamurthy, Anil S wrote:
> > 
> > > Subject: [RFC][Intel-IOMMU] Fix for IOMMU early crash
> > 
> > This patch feels like a huge hack. See below.
>
> You seem to be jumping to conclusion without going in detail. The
> pci_dev struct contains pointer to sysdata, which in turn points to
> the copy of its parent's bus sysdata.  So technically speaking we
> can eliminate sysdata pointer from pci_dev struct which is what one
> portion of this patch does.

... provided nothing relies on this relationship or the existence of
the pci_dev's sysdata. Have you audited every architecture's use of
the sysdata pointers?

> > > This patch removes sysdata from pci_dev struct and creates a new
> > > field called sys_data which is exclusively used by IOMMU driver to
> > > keep its per device context pointer.
> > 
> > Hmpf, why is this needed? with the pci_sysdata work that recently went
> > into mainline we have a void *iommu member in pci_sysdata which should
> > be all that's needed. Please elaborate if it's not enough for your
> > needs.

> I looked at your patch and it was not suitable because I need to
> store iommu private pointer in pci_dev

Could you elaborate on why you need this? I'm assuming it's for the
per-device IOMMU page tables?

> and not in the pci_bus. So I have added a new member sys_data in the
> pci_dev struct. I can change the name from sys_dev to iomu_priv to
> clear the confusion. Do let me know.

Well, you should be able to just use the pci_dev's ->sysdata (that's
what it's there for after all!) but you might need to make it point to
a structure if it's shared, the same way we did with the bus's
->sysdata. I agree that just having it point to the bus's ->sysdata is
not very useful *but* there may be code in the kernel that relies on
it (Calgary did until very recently...) so it would have to be audited
first.

Cheers,
Muli