linux-kernel - Re: [PATCH V2] 2.6.34: simple IOMMU API extension to check safe interrupt remapping

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Date:	Fri, 2 Jul 2010 12:33:58 -0700
From:	Tom Lyon <pugs@...n-about.com>
To:	"Roedel, Joerg" <Joerg.Roedel@....com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"chrisw@...s-sol.org" <chrisw@...s-sol.org>,
	"mst@...hat.com" <mst@...hat.com>,
	"dwmw2@...radead.org" <dwmw2@...radead.org>,
	"aafabbri@...co.com" <aafabbri@...co.com>,
	"scofeldm@...co.com" <scofeldm@...co.com>
Subject: Re: [PATCH V2] 2.6.34: simple IOMMU API extension to check safe interrupt remapping

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@...co.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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