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From: Tom Lyon on 2 Jul 2010 15:40
On Friday 02 July 2010 02:26:46 am Roedel, Joerg wrote:
> On Thu, Jul 01, 2010 at 05:24:32PM -0400, Tom Lyon wrote:
> > This patch allows IOMMU users to determine whether the hardware and software
> > support safe, isolated interrupt remapping. Not all Intel IOMMUs have the
> > hardware, and the software for AMD is not there yet.
> > Signed-off-by: Tom Lyon <pugs(a)cisco.com>
>
> It does not make a lot of sense to check for this feature in the
> IOMMU-API currently because there is no support for intr-remapping in
> there. But it will be there when intr-remapping support for AMD IOMMU is
> implemented. So this change can be considered as a first step in that
> direction. Please repost with the change requested below an I'll add
> this one to my tree.
OK, but I'm not sure what you mean by the first sentence. The Intel stuff
today does intr remapping as a side effect of X2APIC support.

>
> > Version 2: previous ifdefs not needed.
> >
> > MST has convinced me that any user level driver for PCI master devices can't
> > be safe unless there is an IOMMU protecting the APIC MSI/MSI-X interrupt
> > addresses from device writes. This interrupt remapping is not present in all
> > Intel IOMMUs and the code for the interrupt mapping in the AMD IOMMUs is not
> > implemented yet.
> >
> > Needed by not-yet-accepted VFIO driver.
> >
> > diff -uprN linux-2.6.34/drivers/pci/intel-iommu.c iommuapi-linux-2.6.34/drivers/pci/intel-iommu.c
> > --- linux-2.6.34/drivers/pci/intel-iommu.c 2010-05-16 14:17:36.000000000 -0700
> > +++ iommuapi-linux-2.6.34/drivers/pci/intel-iommu.c 2010-06-30 15:47:10.000000000 -0700
> > @@ -3705,6 +3705,10 @@ static int intel_iommu_domain_has_cap(st
> >
> > if (cap == IOMMU_CAP_CACHE_COHERENCY)
> > return dmar_domain->iommu_snooping;
> > + if (cap == IOMMU_CAP_SAFE_INTR_REMAP)
> > + return intr_remapping_enabled;
> >
> > return 0;
> > }
> > diff -uprN linux-2.6.34/include/linux/iommu.h iommuapi-linux-2.6.34/include/linux/iommu.h
> > --- linux-2.6.34/include/linux/iommu.h 2010-05-16 14:17:36.000000000 -0700
> > +++ iommuapi-linux-2.6.34/include/linux/iommu.h 2010-06-30 15:47:34.000000000 -0700
> > @@ -30,6 +30,7 @@ struct iommu_domain {
> > };
> >
> > #define IOMMU_CAP_CACHE_COHERENCY 0x1
> > +#define IOMMU_CAP_SAFE_INTR_REMAP 0x2 /* isolates device intrs */
>
> I think the SAFE_ is not necessary in the name. It is misleading because
> it indicates that there is an unsafe variant of intr-remapping available
> when this capability is not set. Just call it IOMMU_CAP_INTR_REMAPPING.
>
>
> Joerg
>


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