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

[Paul Durrant <xadimgnik@xxxxxxxxx>]

> -----Original Message-----
> From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of Jan 
> Beulich
> Sent: 06 March 2020 13:24
> To: Paul Durrant <xadimgnik@xxxxxxxxx>
> Cc: sstabellini@xxxxxxxxxx; julien@xxxxxxx; Volodymyr_Babchuk@xxxxxxxx; 
> wl@xxxxxxx;
> konrad.wilk@xxxxxxxxxx; andrew.cooper3@xxxxxxxxxx; ian.jackson@xxxxxxxxxxxxx;
> george.dunlap@xxxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxxx; 'David Woodhouse' 
> <dwmw2@xxxxxxxxxxxxx>
> Subject: Re: [Xen-devel] [PATCH 2/2] domain: use PGC_extra domheap page for 
> shared_info
> 
> On 06.03.2020 14:13, Paul Durrant wrote:
> >> -----Original Message-----
> >> From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of Jan 
> >> Beulich
> >> Sent: 06 March 2020 13:10
> >> To: David Woodhouse <dwmw2@xxxxxxxxxxxxx>; Durrant, Paul 
> >> <pdurrant@xxxxxxxxxxxx>
> >> Cc: sstabellini@xxxxxxxxxx; julien@xxxxxxx; wl@xxxxxxx; 
> >> konrad.wilk@xxxxxxxxxx;
> >> andrew.cooper3@xxxxxxxxxx; ian.jackson@xxxxxxxxxxxxx; 
> >> george.dunlap@xxxxxxxxxx; xen-
> >> devel@xxxxxxxxxxxxxxxxxxxx; Volodymyr_Babchuk@xxxxxxxx
> >> Subject: Re: [Xen-devel] [PATCH 2/2] domain: use PGC_extra domheap page 
> >> for shared_info
> >>
> >> On 06.03.2020 13:57, David Woodhouse wrote:
> >>> On Fri, 2020-03-06 at 13:36 +0100, Jan Beulich wrote:
> >>>> And of course this means you're intending to (at least
> >>>> partially) resurrect the distinction between domheap and xenheap,
> >>>> which isn't said anywhere in Paul's series, I don't think.
> >>>
> >>> Right. Secret hiding makes the distinction (xenheap is mapped, domheap
> >>> is not) mostly go away. We are talking about restoring *a* distinction
> >>> between one type of page (Xen ephemeral pages which don't need to be
> >>> preserved over live update) and another (must be preserved), but
> >>> whether that should still be called "xenheap" vs. "domheap", despite
> >>> the massive parallels, isn't entirely clear.
> >>>
> >>>>  If this
> >>>> is a sufficiently correct understanding of mine, then on one hand
> >>>> I start seeing the point of the conversion Paul wants to make, but
> >>>> otoh this then feels a little like making the 2nd step before the
> >>>> 1st.
> >>>
> >>>
> >>> What would you suggest is the first step?
> >>
> >> Establishing of what the new separation rule and mechanism is going
> >> to be (no matter how the two resulting pieces are going to be
> >> named).
> >>
> >
> > Would you be ok with a comment to that effect?
> 
> Not sure. It would certainly help if the cover letter at least
> mentioned other related aspects like this one.
> 
> > My aim is to make the separation abundantly obvious by getting rid
> > of shared xenheap pages (for non-system domains at least) but I
> > can't do that before converting shared_info and grant shared/status
> > frames to domheap.
> 
> Following David's various replies - instead of going this route of
> replacing the sharing of xenheap pages by different logic, the
> same ought to be achievable by making the backing allocations come
> from the correct pool?
> 

I still prefer the simplification of not having to clean up the shared xenheap 
page list in domain_kill() so IMO it is still worth it for that alone.

  Paul


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