linux-kernel - Re: [PATCH 2/2] iommu: dmar -- reserve mmio space used by IOMMU

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Date:	Wed, 6 Jun 2012 10:29:00 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Don Dutile <ddutile@...hat.com>, iommu@...ts.linux-foundation.org,
	mingo@...e.hu, linux-kernel@...r.kernel.org, chrisw@...hat.com,
	suresh.b.siddha@...el.com
Subject: Re: [PATCH 2/2] iommu: dmar -- reserve mmio space used by IOMMU


* David Woodhouse <dwmw2@...radead.org> wrote:

> On Wed, 2012-06-06 at 10:16 +0200, Ingo Molnar wrote:
>
> > So basically the patch-set is fine as-is, we just want a 
> > sufficiently nasty sounding warning message about the BIOS 
> > bug,
> 
> No. The other change that's required is that the warning and 
> the workaround need to trigger even when IOMMU support isn't 
> built into the kernel. This BIOS bug can bite you even when 
> you aren't *using* the IOMMU.

Right, but that's the status quo and most of the time (distro 
kernels) the driver is available, right?

So for all practical purposes we get 99% of the warning power 
without going into chicken-and-egg problems like how do we 
determine that there's an IOMMU area there if there's no IOMMU 
aware code in the kernel, right?

Thanks,

	Ingo
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