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

[Mukesh Rathor <mukesh.rathor@oracle.com>]

On Sat, 24 May 2014 01:08:49 +0200
Tim Deegan <tim@xen.org> wrote:

> At 15:37 -0700 on 23 May (1400855820), Mukesh Rathor wrote:
> > On Fri, 23 May 2014 21:05:34 +0200
> > Tim Deegan <tim@xen.org> 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.

Good point, but Jan had a concern on that when I had dropped the if
statement completely, that it would allow HVM guests to go thru. 
Hence !is_pvh to let hvm guest continue to fail.

thanks,
mukesh