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

From: Stefano Stabellini
Date: Mon Aug 10 2015 - 07:27:01 EST

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@xxxxxxxxxx>
> >
> > 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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