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

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

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?

Thanks,
Tamas

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