Re: [Xen-devel] [V9 PATCH 6/8] pvh dom0: Add and remove foreign pages

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.04.14 at 02:28, <mukesh.rathor@xxxxxxxxxx> wrote:
> On Tue, 22 Apr 2014 08:28:45 +0100
> "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
> 
>> >>> On 22.04.14 at 02:19, <mukesh.rathor@xxxxxxxxxx> wrote:
>> > On Wed, 16 Apr 2014 18:37:42 -0700
>> > Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> wrote:
>> > 
>> >> On Wed, 16 Apr 2014 17:00:35 +0100
>> >> "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
>> >> 
> ............
> 
>> >      /* following will take a refcnt on the mfn */
>> >      page = get_page_from_gfn(fdom, fgfn, &p2mt, P2M_ALLOC);
>> > -    if ( !page || !p2m_is_valid(p2mt) )
>> > +    if ( !page || !p2m_is_strict_ram(p2mt) )
>> >      {
>> >          if ( page )
>> >              put_page(page);
>> > diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
>> > index 47604da..e0bf6dc 100644
>> > --- a/xen/include/asm-x86/p2m.h
>> > +++ b/xen/include/asm-x86/p2m.h
>> > @@ -165,6 +165,7 @@ typedef unsigned int p2m_query_t;
>> >  
>> >  /* Useful predicates */
>> > +#define p2m_is_strict_ram(_t) (p2m_to_mask(_t) &
>> > p2m_to_mask(p2m_ram_rw))
>> 
>> Not sure - this now precludes mapping log-dirty or r/o pages, i.e. I
>> think you went from too relaxed to too strict. I think the question
>> needs answering in a more abstract fashion first, i.e. without code
>> written immediately: Which pages absolutely need to be foreign-
>> mappable and which ones can safely get foreign-mapped. My first
>> thought would be P2M_RAM_TYPES & ~P2M_HOLE_TYPES, with
>> P2M_HOLE_TYPES contained in P2M_RAM_TYPES generating a kind
>> of -EAGAIN notification while triggering the re-creation of the page
>> (which already is an indication that instead of P2M_HOLE_TYPES it
>> might well need to be P2M_PAGING_TYPES).
> 
> The current use case is p2m_ram_rw, my approach would be start with 
> minimum and add more as needed when features like migration, passthru, etc
> are added. My understanding of the various p2m types is limited, so I
> am at your mercy here to advise what types to anticipate. IMO, just
> checking for P2M_RAM_TYPES might suffice, I can additionally add check
> to make sure it's not P2M_HOLE_TYPES. Please lmk.

It's clear that p2m_ram_rw is too narrow: p2m_ram_ro and
p2m_ram_logdirty will minimally also need accepting here. As for the
paging/paged and shared types, I have to defer to the respective
maintainers - Andres, Tim?

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel