Re: [PATCH 07/10] xen/arm: intruduce alloc_domstatic_pages

[Julien Grall <julien@xxxxxxx>]

On 19/05/2021 08:52, Penny Zheng wrote:
> Hi Julien
Hi Penny,

> > -----Original Message-----
> > From: Julien Grall <julien@xxxxxxx>
> > Sent: Tuesday, May 18, 2021 8:13 PM
> > To: Penny Zheng <Penny.Zheng@xxxxxxx>; Jan Beulich <jbeulich@xxxxxxxx>
> > Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>; Wei Chen
> > <Wei.Chen@xxxxxxx>; nd <nd@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx;
> > sstabellini@xxxxxxxxxx
> > Subject: Re: [PATCH 07/10] xen/arm: intruduce alloc_domstatic_pages
> >
> > Hi Penny,
> >
> > On 18/05/2021 09:57, Penny Zheng wrote:
> > > > -----Original Message-----
> > > > From: Jan Beulich <jbeulich@xxxxxxxx>
> > > > Sent: Tuesday, May 18, 2021 3:35 PM
> > > > To: Penny Zheng <Penny.Zheng@xxxxxxx>
> > > > Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>; Wei Chen
> > > > <Wei.Chen@xxxxxxx>; nd <nd@xxxxxxx>; xen-
> > devel@xxxxxxxxxxxxxxxxxxxx;
> > > > sstabellini@xxxxxxxxxx; julien@xxxxxxx
> > > > Subject: Re: [PATCH 07/10] xen/arm: intruduce alloc_domstatic_pages
> > > >
> > > > On 18.05.2021 07:21, Penny Zheng wrote:
> > > > > --- a/xen/common/page_alloc.c
> > > > > +++ b/xen/common/page_alloc.c
> > > > > @@ -2447,6 +2447,9 @@ int assign_pages(
> > > > >        {
> > > > >            ASSERT(page_get_owner(&pg[i]) == NULL);
> > > > >            page_set_owner(&pg[i], d);
> > > > > +        /* use page_set_reserved_owner to set its reserved domain owner.
> > > > */
> > > > > +        if ( (pg[i].count_info & PGC_reserved) )
> > > > > +            page_set_reserved_owner(&pg[i], d);
> > > > Now this is puzzling: What's the point of setting two owner fields to
> > > > the same value? I also don't recall you having introduced
> > > > page_set_reserved_owner() for x86, so how is this going to build there?
> > > Thanks for pointing out that it will fail on x86.
> > > As for the same value, sure, I shall change it to domid_t domid to record its
> > reserved owner.
> > > Only domid is enough for differentiate.
> > > And even when domain get rebooted, struct domain may be destroyed, but
> > > domid will stays The same.
> > > Major user cases for domain on static allocation are referring to the
> > > whole system are static, No runtime creation.
> > One may want to have static memory yet doesn't care about the domid. So I
> > am not in favor to restrict about the domid unless there is no other way.
> The user case you bring up here is that static memory pool?
No. The use case I am talking about is an user who wants to give a 
specific memory region to the guest but doesn't care about which domid 
was allocated to the guest.
> Right now, the user cases are mostly restricted to static system.
> If we bring runtime allocation, `xl` here, it will add a lot more complexity.
> But if the system has static behavior, the domid is also static.
I read this as the admin would have to specify the domain ID in the 
Device-Tree. Is that what you meant?
If so, then I don't see why we should mandate that. I would mind less if 
by static you mean the domid will be allocated by Xen and then not 
changed accross reboot.
> On rebooting domain from static memory pool, it brings up more discussion, like
> do we intend to give the memory back to static memory pool when rebooting,
> if so, ram could be allocated from different place compared with the previous 
> one.
You should have all the information in the Device-Tree to re-assign the 
correct regions. So why would it be allocated from a different place?
Cheers,

--
Julien Grall