RE: [PATCH v6 5/7] xen: re-define assign_pages and introduce a new function assign_page

[Penny Zheng <Penny.Zheng@xxxxxxx>]

Hi Jan and Stefano

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: Thursday, September 9, 2021 5:06 PM
> To: Penny Zheng <Penny.Zheng@xxxxxxx>
> Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>; Wei Chen
> <Wei.Chen@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx;
> sstabellini@xxxxxxxxxx; julien@xxxxxxx
> Subject: Re: [PATCH v6 5/7] xen: re-define assign_pages and introduce a new
> function assign_page
> 
> On 08.09.2021 11:52, Penny Zheng wrote:
> > In order to deal with the trouble of count-to-order conversion when
> > page number is not in a power-of-two, this commit re-define
> > assign_pages for nr pages and introduces a new helper assign_page for
> original page with a single order.
> >
> > Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
> 

Stefano, Since I need to re-commit this one, I'll add-in your NIT suggestion in 
commit 7("
xen/arm: introduce allocate_static_memory"), and push a new Serie asap. ;)

> I have to admit that I'm now very puzzled: Instead of restoring the long 
> agreed
> upon ordering of parameters (and then keeping my A-b), you've dropped the
> ack.
> 
> > --- a/xen/arch/x86/pv/dom0_build.c
> > +++ b/xen/arch/x86/pv/dom0_build.c
> > @@ -568,7 +568,7 @@ int __init dom0_construct_pv(struct domain *d,
> >          else
> >          {
> >              while ( count-- )
> > -                if ( assign_pages(d, mfn_to_page(_mfn(mfn++)), 0, 0) )
> > +                if ( assign_pages(d, mfn_to_page(_mfn(mfn++)), 1, 0)
> > + )
> 
> This change alone demonstrates the problem when it comes to backporting
> future changes: If the original patch contained a code addition similar to 
> what
> you change to, without the person doing the backporting paying close
> attention, the result will be an order-1 request when an order-0 one is 
> wanted.
> It was explained to you that in order to make people doing backports aware of
> this semantic change, the order of parameters of the function ought to be
> altered. That way the compiler will complain, and the person will know to look
> closely what adjustments are needed.
> 
> In this context I find it further puzzling ...
> 
> > --- a/xen/include/xen/mm.h
> > +++ b/xen/include/xen/mm.h
> > @@ -133,8 +133,14 @@ void heap_init_late(void);
> >
> >  int assign_pages(
> >      struct domain *d,
> > +    struct page_info *pg,
> > +    unsigned long nr,
> > +    unsigned int memflags);
> > +
> > +int assign_page(
> >      struct page_info *pg,
> >      unsigned int order,
> > +    struct domain *d,
> >      unsigned int memflags);
> 
> ... that you also neglected the request to harmonize the argument order of
> both functions. What we want (and what I thought has long been agreed
> upon) is e.g.
> 
> int assign_pages(
>     struct page_info *pg,
>     unsigned long nr,
>     struct domain *d,
>     unsigned int memflags);
> 
> int assign_page(
>     struct page_info *pg,
>     unsigned int order,
>     struct domain *d,
>     unsigned int memflags);
> 

Sorry, my fault, I've wrongly interpretate julien's harmonize request twice.
 
> Jan