linux-kernel - Re: [PATCH v2 2/2] Intel-IOMMU, intr-remap: source-id checking

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Message-ID: <m1r5ykm180.fsf@fess.ebiederm.org>
Date:	Wed, 20 May 2009 05:02:23 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Joerg Roedel <joerg.roedel@....com>
Cc:	Ingo Molnar <mingo@...e.hu>, Yinghai Lu <yinghai@...nel.org>,
	Weidong Han <weidong.han@...el.com>, dwmw2@...radead.org,
	suresh.b.siddha@...el.com, linux-kernel@...r.kernel.org,
	iommu@...ts.linux-foundation.org, kvm@...r.kernel.org
Subject: Re: [PATCH v2 2/2] Intel-IOMMU, intr-remap: source-id checking

Joerg Roedel <joerg.roedel@....com> writes:

> On Wed, May 20, 2009 at 10:21:14AM +0200, Ingo Molnar wrote:
>> 
>> * Eric W. Biederman <ebiederm@...ssion.com> wrote:
>> > Being a major nitpick, I have to point out that the code is not 
>> > structured to support other iommus, and I think AMD has one that 
>> > can do this as well.
>> 
>> (Joerg Cc:-ed)
>
> The AMD IOMMU does also have an interrupt remapping feature. But it is
> currently unsupported in the Linux driver. When this is going to be
> implemented I think we can go the same way as for device passthrough in
> KVM. This was an Intel-only feature too and was later adapted to support
> AMD IOMMU too.

The Intel IOMMU is also interesting because it allows traffic from
buggy ioapcis to be remapped safely in process context, adding a large
margin of safety and flexibility to the existing irq migration
and cpu hotunplug scenarios.

Can we use the AMD IOMMU to achieve the same objective?

I would really like to say from point X on AMD and Intel systems don't
have to worry about irq migrations used caused by old buggy ioapic
state machines, which I have previously confirmed in both AMD and
Intel ioapics.

Eric
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