Re: [Xen-devel] [PATCH v3 5/6] mm: add 'is_special_page' macro...

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Thu, Mar 5, 2020 at 8:38 AM Durrant, Paul <pdurrant@xxxxxxxxxxxx> wrote:
>
> > -----Original Message-----
> > From: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
> > Sent: 05 March 2020 15:10
> > To: pdurrant@xxxxxxxx
> > Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>; Durrant, Paul 
> > <pdurrant@xxxxxxxxxxxx>; Jan Beulich
> > <jbeulich@xxxxxxxx>; Andrew Cooper <andrew.cooper3@xxxxxxxxxx>; Wei Liu 
> > <wl@xxxxxxx>; Roger Pau Monné
> > <roger.pau@xxxxxxxxxx>; George Dunlap <george.dunlap@xxxxxxxxxx>; Ian 
> > Jackson
> > <ian.jackson@xxxxxxxxxxxxx>; Julien Grall <julien@xxxxxxx>; Konrad 
> > Rzeszutek Wilk
> > <konrad.wilk@xxxxxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>; Tim 
> > Deegan <tim@xxxxxxx>
> > Subject: RE: [EXTERNAL][PATCH v3 5/6] mm: add 'is_special_page' macro...
> >
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> >
> > On Thu, Mar 5, 2020 at 5:45 AM <pdurrant@xxxxxxxx> wrote:
> > >
> > > From: Paul Durrant <pdurrant@xxxxxxxxxx>
> > >
> > > ... to cover xenheap and PGC_extra pages.
> > >
> > > PGC_extra pages are intended to hold data structures that are associated
> > > with a domain and my be mapped by that domain. They should not be treated
> > > as 'normal' guest pages (i.e. RAM or page tables). Hence, in many cases
> > > where code currently tests is_xen_heap_page() it should also check for
> > > the PGC_extra bit in 'count_info'.
> > >
> > > This patch therefore defines is_special_page() to cover both cases and
> > > converts tests if is_xen_heap_page() to is_special_page() where
> > > appropriate.
> >
> > In context of VM forking, are these pages only used by some type of PV
> > mechanism? If not, would we need to get them copied somehow or are
> > these setup during the regular createdomain routine? Can they be
> > copied on-demand, ie. do these pages pass a p2m_is_ram() check?
>
> PGC_extra domheap pages are intended as direct replacements for shared 
> xenheap pages and should be treated the same way. Thus they do not form part 
> of the migration stream. Their p2m type depends entirely on how they are 
> added to the p2m, as it is for any other page.

OK, thanks. For the mem_sharing bits:

Acked-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>

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