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Re: [Xen-devel] [PATCH 2/2] domain: use PGC_extra domheap page for shared_info

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: 26 February 2020 13:58
> To: Durrant, Paul <pdurrant@xxxxxxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Stefano Stabellini
> <sstabellini@xxxxxxxxxx>; Julien Grall <julien@xxxxxxx>; Volodymyr Babchuk
> <Volodymyr_Babchuk@xxxxxxxx>; Andrew Cooper <andrew.cooper3@xxxxxxxxxx>;
> George Dunlap <george.dunlap@xxxxxxxxxx>; Ian Jackson
> <ian.jackson@xxxxxxxxxxxxx>; Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx>; Wei Liu <wl@xxxxxxx>
> Subject: Re: [PATCH 2/2] domain: use PGC_extra domheap page for
> shared_info
> On 25.02.2020 10:53, Paul Durrant wrote:
> > There's no particular reason shared_info need use a xenheap page. It's
> > only purpose is to be mapped by the guest so use a PGC_extra domheap
> page
> > instead.
> Since the cover letter also doesn't give any background - is there a
> problem with the current arrangements? Are there any further plans
> depending on this being changed? Or is this simply "let's do it
> because now we can"?

The general direction is to get rid of shared xenheap pages. Knowing that a 
xenheap page is not shared with a guest makes dealing with live update much 
easier, and also allows a chunk of code to be removed from 
domain_relinquish_resoureses() (the shared xenheap walk which de-assigns them 
from the dying guest).
The only xenheap pages shared with a normal domU (as opposed to a system 
domain, which would be re-created on live update anyway) are AFAICT shared-info 
and grant table/status frames. This series deals with shared-info but I do have 
proto-patches for the grant table code too.

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