linux-kernel - Re: [Xen-devel] [PATCH v3 09/20] xen/biomerge: Don't allow biovec to be merge when Linux is not using 4KB page

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Date:	Mon, 10 Aug 2015 12:24:20 +0100
From:	Julien Grall <julien.grall@...rix.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	<ian.campbell@...rix.com>, <linux-kernel@...r.kernel.org>,
	David Vrabel <david.vrabel@...rix.com>,
	<xen-devel@...ts.xenproject.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Xen-devel] [PATCH v3 09/20] xen/biomerge: Don't allow biovec
 to be merge when Linux is not using 4KB page

Hi Stefano,

On 10/08/15 11:50, Stefano Stabellini wrote:
> On Fri, 7 Aug 2015, Julien Grall wrote:
>> On ARM all dma-capable devices on a same platform may not be protected
>> by an IOMMU. The DMA requests have to use the BFN (i.e MFN on ARM) in
>> order to use correctly the device.
>>
>> While the DOM0 memory is allocated in a 1:1 fashion (PFN == MFN), grant
>> mapping will screw this contiguous mapping.
>>
>> When Linux is using 64KB page granularitary, the page may be split
>> accross multiple non-contiguous MFN (Xen is using 4KB page
>> granularity). Therefore a DMA request will likely fail.
>>
>> Checking that a 64KB page is using contiguous MFN is tedious. For
>> now, always says that biovec are not mergeable.
>>
>> Signed-off-by: Julien Grall <julien.grall@...rix.com>
> 
> Please fix the grammar in the subject line.

If I made a mistake it's unlikely that I will find myself which one I made.

Anyway, I guess you mean to replace merge by merged? I don't see any
other in the subject.

Regards,

-- 
Julien Grall
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