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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Message-ID: <alpine.DEB.2.02.1508101224220.11337@kaball.uk.xensource.com>
Date:	Mon, 10 Aug 2015 12:25:27 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Julien Grall <julien.grall@...rix.com>
CC:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	<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

On Mon, 10 Aug 2015, Julien Grall wrote:
> 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.

yes and page/pages:

xen/biomerge: Don't allow biovec's to be merged when Linux is not using 4KB pages
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