linux-kernel - Re: [PATCH 05/16] iommu/amd: Split device table initialization into irq and dma part

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Date:	Fri, 28 Sep 2012 16:25:55 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	<iommu@...ts.linux-foundation.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 05/16] iommu/amd: Split device table initialization into
 irq and dma part

On Fri, Sep 28, 2012 at 10:17:53AM -0400, Konrad Rzeszutek Wilk wrote:
> On Fri, Sep 28, 2012 at 02:23:55PM +0200, Joerg Roedel wrote:
> > When the IOMMU is enabled very early (as with irq-remapping)
> > some devices are still in BIOS hand. When dma is blocked
> > early this can cause lots of IO_PAGE_FAULTs. So delay the
> > DMA initialization and do it right before the dma_ops are
> > initialized.
> > To be secure, block all interrupts by default when irq-remapping is
> 
> What are you trying to be secure against?

Against attacks of faked MSI msgs that could DoS the system. MSI
messages are only specific DMA transactions in the end and a guest with
a device assigned has control over its DMA engine and can thus send
arbitrary interrupt requests to the host. There is a whole paper about
such attacks. I can't find right now, but I send you  a link when I find
it.

	Joerg

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