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RE: [PATCH v9 6/8] xen/arm: unpopulate memory when domain is static
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Penny Zheng <Penny.Zheng@xxxxxxx>
- Date: Tue, 26 Jul 2022 02:57:42 +0000
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- Cc: Wei Chen <Wei.Chen@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
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- Thread-topic: [PATCH v9 6/8] xen/arm: unpopulate memory when domain is static
Hi Jan
> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: Monday, July 25, 2022 11:36 PM
> To: Penny Zheng <Penny.Zheng@xxxxxxx>
> Cc: Wei Chen <Wei.Chen@xxxxxxx>; Andrew Cooper
> <andrew.cooper3@xxxxxxxxxx>; George Dunlap <george.dunlap@xxxxxxxxxx>;
> Julien Grall <julien@xxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>;
> Wei Liu <wl@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH v9 6/8] xen/arm: unpopulate memory when domain is
> static
>
> On 20.07.2022 07:46, Penny Zheng wrote:
> > Today when a domain unpopulates the memory on runtime, they will
> > always hand the memory back to the heap allocator. And it will be a
> > problem if domain is static.
> >
> > Pages as guest RAM for static domain shall be reserved to only this
> > domain and not be used for any other purposes, so they shall never go
> > back to heap allocator.
> >
> > This commit puts reserved pages on the new list resv_page_list only
> > after having taken them off the "normal" list, when the last ref dropped.
>
> I guess this wording somehow relates to ...
>
> > --- a/xen/common/page_alloc.c
> > +++ b/xen/common/page_alloc.c
> > @@ -2674,10 +2674,14 @@ void free_domstatic_page(struct page_info
> > *page)
> >
> > drop_dom_ref = !domain_adjust_tot_pages(d, -1);
> >
> > - spin_unlock_recursive(&d->page_alloc_lock);
> > -
> > free_staticmem_pages(page, 1, scrub_debug);
> >
> > + /* Add page on the resv_page_list *after* it has been freed. */
> > + if ( !drop_dom_ref )
> > + page_list_add_tail(page, &d->resv_page_list);
>
> ... the conditional used here. I cannot, however, figure why there is this
> conditional (and said part of the description also doesn't help me figure it
> out).
>
I was thinking that if drop_dom_ref true, then later the whole domain struct
will be released, then there is no need to add the page to d->resv_page_list
> As an aside: A title prefix of xen/arm: suggests you're mostly touching Arm
> code. But you're touching exclusively common code here.
> I for one would almost have skipped this patch (more than once) when
> deciding which ones (may) want me looking at them.
>
Sorry for that, I’ll fix it
> Jan
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