linux-kernel - Re: [PATCH v4 2/7] iommu/core: split mapping to page sizes as supported by the hardware

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Date:	Thu, 10 Nov 2011 15:51:10 +0100
From:	Joerg Roedel <Joerg.Roedel@....com>
To:	cody <mail.kai.huang@...il.com>
CC:	Ohad Ben-Cohen <ohad@...ery.com>,
	<iommu@...ts.linux-foundation.org>, <linux-omap@...r.kernel.org>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	David Woodhouse <dwmw2@...radead.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	David Brown <davidb@...eaurora.org>,
	Arnd Bergmann <arnd@...db.de>, <linux-kernel@...r.kernel.org>,
	Hiroshi Doyu <hdoyu@...dia.com>,
	Stepan Moskovchenko <stepanm@...eaurora.org>,
	KyongHo Cho <pullip.cho@...sung.com>, <kvm@...r.kernel.org>
Subject: Re: [PATCH v4 2/7] iommu/core: split mapping to page sizes as
 supported by the hardware

On Thu, Nov 10, 2011 at 10:35:34PM +0800, cody wrote:
> Yes I totally agree page-size is not required for unmap operations
> and should not be added as parameter to map/unmap operations. I am
> not saying the unmap operation, but the IOTLB flush operation. My
> point is we also may also need to add similar logic in IOTLB flush
> code (such as in Intel IOMMU dirver) to grantee that when issuing
> IOTLB flush command for large page, we will still meet the hardware
> limitation of flushing large page. Seems for Intel IOMMU the only
> limitation is the mask value (indicating number of 4k-pages) cannot
> be smaller than the value to cover large page, and seems current
> Intel IOMMU driver code has covered this case well. I am not
> familiar with how AMD IOMMU issues IOTLB flush command, it should be
> able to handle this large page case too. So at this moment, this
> patch should not have any issues :)

The map-operation actually takes a size, as it should. The idea is to
change this function to a map_page interface which takes a page-size
parameter, but thats another story.
The IOTLB flushing is not exposed by the IOMMU-API anyway. To whatever
is necessary to do that, it is the business of the IOMMU driver. So in
the unmap-path the driver finds out the page-size to unmap and can
immediatly flush the IOTLB for that page.


	Joerg

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