linux-kernel - Re: [PATCH]intel-iommu batched iotlb flushes

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Message-ID: <20080212155448.GC27490@linux.intel.com>
Date:	Tue, 12 Feb 2008 07:54:48 -0800
From:	mark gross <mgross@...ux.intel.com>
To:	David Miller <davem@...emloft.net>
Cc:	muli@...ibm.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH]intel-iommu batched iotlb flushes

On Tue, Feb 12, 2008 at 01:00:06AM -0800, David Miller wrote:
> From: Muli Ben-Yehuda <muli@...ibm.com>
> Date: Tue, 12 Feb 2008 10:52:56 +0200
> 
> > The streaming DMA-API was designed to conserve IOMMU mappings for
> > machines where IOMMU mappings are a scarce resource, and is a poor
> > fit for a modern IOMMU such as VT-d with a 64-bit IO address space
> > (or even an IOMMU with a 32-bit address space such as Calgary) where
> > there are plenty of IOMMU mappings available.
> 
> For the 64-bit case what you are suggesting eventually amounts
> to mapping all available RAM in the IOMMU.

Something could be done:
we could enable drivers to have DMA-pools they manage that get mapped
and are re-used.

I would rather the DMA-pools be tied to PID's that way any bad behavior
would be limited to the address space of the process using the device.
I haven't thought about how hard this would be to do but it would be
nice.  I think this could be tricky.

Application sets up ring buffer of device DMA memory, passes this to
driver/stack.  Need to handle hitting high water marks and application
exit clean up sanely... 

--mgross

> 
> Although an extreme version of your suggestion, it would be the
> most efficient as it would require zero IOMMU flush operations.
> 
> But we'd lose things like protection and other benefits.
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