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

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Message-ID: <20100702092646.GF24084@amd.com>
Date:	Fri, 2 Jul 2010 11:26:46 +0200
From:	"Roedel, Joerg" <Joerg.Roedel@....com>
To:	Tom Lyon <pugs@...co.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 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.

> 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

-- 
Joerg Roedel - AMD Operating System Research Center

Advanced Micro Devices GmbH Einsteinring 24 85609 Dornach
General Managers: Alberto Bozzo, Andrew Bowd
Registration: Dornach, Landkr. Muenchen; Registerger. Muenchen, HRB Nr. 43632

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