linux-kernel - Re: [PATCH] iommu: Include MSI susceptibility to DMA in creating iommu groups

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Message-ID: <20111118104651.GJ5627@amd.com>
Date:	Fri, 18 Nov 2011 11:46:51 +0100
From:	Joerg Roedel <Joerg.Roedel@....com>
To:	Alex Williamson <alex.williamson@...hat.com>
CC:	<iommu@...ts.linux-foundation.org>, <dwmw2@...radead.org>,
	<linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iommu: Include MSI susceptibility to DMA in creating
 iommu groups

On Thu, Nov 17, 2011 at 10:09:26AM -0700, Alex Williamson wrote:
> IOMMU drivers should account for the platform's susceptibility to
> DMA triggered MSI interrupts in creating IOMMU groups.  Skip
> devices when the IOMMU can't isolate MSI from DMA, but allow
> an iommu=group_unsafe_msi option for opt-in.  This removes the
> leap in logic for users that IOMMU_CAP_INTR_REMAP is required for
> interrupt security when they may be running on a non-x86 platform
> that does not have this dependency.

I actually don't see the point in this. The iommu-group thing is to tell
user-space what devices the IOMMU can safely distinguish between. The
absence of interrupt-remapping changes nothing to that grouping. So why
remove it when interrupt remapping is not enabled?

	Joerg

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