Re: [Xen-devel] [PATCH v4 1/6] xen: improve changes to xen_add_to_physmap

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Fri, 14 Sep 2012 16:54:06 +0100
Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> wrote:

> On Fri, 14 Sep 2012, Ian Campbell wrote:
> > On Fri, 2012-09-14 at 16:44 +0100, Stefano Stabellini wrote:
> > > On Fri, 14 Sep 2012, Jan Beulich wrote:
> > > > >>> On 14.09.12 at 15:56, Ian Campbell
> > > > >>> <Ian.Campbell@xxxxxxxxxx> wrote:
> > > > >> > > Might we prefer to have a batched version of this call?
> > > > >> > > I don't think we can shoehorn the necessary fields into
> > > > >> > > xen_add_to_physmap_t though.
> > > > >> > 
> > > > >> > Actually, talking about this we Stefano we think we can.
> > > > >> > Since both idx and gpfn are unsigned longs they can become
> > > > >> > unions with a GUEST_HANDLE without changing the ABI on
> > > > >> > x86_32 or x86_64.
> > > > > 
> > > > > Except we need both foreign_domid and size, which currently
> > > > > overlap, and there's no other spare bits. Damn.
> > > > > 
> > > > > Looks like XENMEM_add_to_physmap_range is the only option :-(
> > > > 
> > > > You could use the first entry in each array to specify the
> > > > counts, which would at once allow mixed granularity on each
> > > > list (should that ever turn out useful); initially you would
> > > > certainly want both counts to match.
> > > 
> > > I think it would be better from the interface point of view to
> > > have idx become the number of frames, and gpfn a pointer (a
> > > GUEST_HANDLE) to a struct that contains both arrays.
> > 
> > We'd need to slip in enough info to allow continuations too. Perhaps
> > that can be done by manipulating the size and the handle to keep
> > track of progress. Or maybe we can get away with just just frobbing
> > the size if we process the array backwards.
> > 
> > Which is all sounding pretty gross. I'm very temped to add
> > add_to_physmap2...
> 
> Yeah, I am OK with that.

Agree, pmap2.



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