Re: [Xen-devel] [V15 PATCH 1/2] pvh dom0: Add and remove foreign pages

[Tim Deegan <tim@xxxxxxx>]

At 15:37 -0700 on 23 May (1400855820), Mukesh Rathor wrote:
> On Fri, 23 May 2014 21:05:34 +0200
> Tim Deegan <tim@xxxxxxx> wrote:
> 
> > At 16:30 -0700 on 22 May (1400772630), Mukesh Rathor wrote:
> > > In this patch, a new function, p2m_add_foreign(), is added
> > > to map pages from a foreign guest into dom0 for various purposes
> > > like domU creation, running xentrace, etc... Such pages are
> > > typed p2m_map_foreign.  Note, it is the nature of such pages
> > > that a refcnt is held during their stay in the p2m. The
> > > refcnt is added and released in the low level ept function
> > > atomic_write_ept_entry. That macro is converted to a function to
> > > allow for such refcounting, which only applies to leaf entries in
> > > the ept. Furthermore, please note that paging/sharing is disabled
> > > if the controlling or hardware domain is pvh. Any enabling of those
> > > features would need to ensure refcnt are properly maintained for
> > > foreign types, or paging/sharing is skipped for foreign types.
> > > 
> > > Also, we change get_pg_owner so it allows foreign mappings for pvh.
> > 
> > But you no longer actually call get_pg_owner() for PVH domains, right?
> > So that hunk should go away.  With that done,
> 
> Hi Tim,
> 
> We actually need get_pg_owner for the mmuext call by the toolstack 
> when building a PV domain, doing pinning operations on the guest table.

Ah, I see.  Let's handle that in a separate patch then, since it's
now unrelated to foreign mappings in PVH any more.

Having the change where it is seems fine, but I think the correct test
is (is_pv() && paging_mode_translate()) rather than (!is_pvh() &&
paging_mode_translate()) -- it's a weakness of the PV pagetable ops
that's being avoided here, rather than any special treatment for PVH.

Cheers,

Tim.

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