RE: [PATCH v1 4/5] xen/arm: retrieve reserved pages on populate_physmap

[Penny Zheng <Penny.Zheng@xxxxxxx>]

Hi Jan

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: Wednesday, March 30, 2022 5:59 PM
> To: Penny Zheng <Penny.Zheng@xxxxxxx>
> Cc: Wei Chen <Wei.Chen@xxxxxxx>; Henry Wang <Henry.Wang@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 v1 4/5] xen/arm: retrieve reserved pages on
> populate_physmap
> 
> On 30.03.2022 11:36, Penny Zheng wrote:
> > --- a/xen/common/memory.c
> > +++ b/xen/common/memory.c
> > @@ -249,6 +249,26 @@ static void populate_physmap(struct memop_args
> *a)
> >
> >                  mfn = _mfn(gpfn);
> >              }
> > +#ifdef CONFIG_STATIC_MEMORY
> > +            else if ( is_domain_on_static_allocation(d) )
> > +            {
> > +                for ( j = 0; j < (1U << a->extent_order); j++ )
> > +                {
> > +                    page = page_list_remove_head(&d->resv_page_list);
> 
> How do you guarantee the pages are contiguous, as required by a non-zero
> a->extent_order? Did you perhaps mean to forbid non-zero-order requests
> in this configuration?,

True, true, thanks for pointing that out.
I would not intend to add complex algorithm here to find contiguous pages of 
requested
order, forbidding non-zero-order with error message shall be added here.

> 
> > +                    if ( unlikely(!page) )
> > +                    {
> > +                        gdprintk(XENLOG_INFO,
> > +                                 "Could not allocate guest page number 
> > %lx\n",
> > +                                 gfn_x(_gfn(gpfn)));
> > +                        goto out;
> 
> And earlier allocated pages are simply lost / leaked?
> 

That was unconsidered, thanks for pointing that out.
Since now we are forbidding non-zero-order requests, earlier allocated pages 
shall
not need to be considered.
 
> Jan