Re: [Xen-devel] [PATCH LINUX RFC] xen: privcmd: implement IOCTL_PRIVCMD_MMAPBATCH_V2_UNCACHED

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2013-12-20 at 09:13 -0500, Konrad Rzeszutek Wilk wrote:
> On Fri, Dec 20, 2013 at 09:19:13AM +0000, Ian Campbell wrote:
> > On Wed, 2013-12-18 at 16:16 -0500, Konrad Rzeszutek Wilk wrote:
> > > On Wed, Dec 18, 2013 at 05:30:37PM +0000, Ian Campbell wrote:
> > > > On ARM we want to use uncached foreign mappings while building the 
> > > > domain
> > > > because the guests start with MMU and caches disabled.
> > > > 
> > > 
> > > Why introduce a new ioctl? Could we piggyback on the old one and on ARM
> > > do the uncached.
> > 
> > Because there are (going to be) other circumstances where we do want a
> > cached foreign mapping, specifically migration.
> 
> Why not then just expand the existing ioctl with a flag? ARM after all
> is still experimental so you could do that.

Well, ARM just uses the same ioctl as on x86, so we wouldn't be
expanding, but duplicating, which didn't seem worth it.

And secondly, unlike hypercalls, the ioctls are part of Linux's
interface, so I'm not sure how changing them would go down.

Ian.


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