Re: [Xen-devel] [PATCH v5 1/4] xen: move steal_page and donate_page to common code

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 10 Sep 2013, Jan Beulich wrote:
> >>> On 09.09.13 at 18:06, Stefano Stabellini 
> >>> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> > --- a/xen/common/memory.c
> > +++ b/xen/common/memory.c
> > @@ -230,6 +230,91 @@ int guest_remove_page(struct domain *d, unsigned long 
> > gmfn)
> >      return 1;
> >  }
> >  
> > +int donate_page(
> > +    struct domain *d, struct page_info *page, unsigned int memflags)
> > +{
> > +    spin_lock(&d->page_alloc_lock);
> > +
> > +    if ( is_xen_heap_page(page) || (page_get_owner(page) != NULL) )
> > +        goto fail;
> > +
> > +    if ( d->is_dying )
> > +        goto fail;
> > +
> > +    if ( page->count_info & ~(PGC_allocated | 1) )
> 
> While the literal 1 was acceptable in arch specific code, I'm not sure
> it really is in generic code. Nothing enforces that an arch has the
> count starting at bit 0. Even if it reads a little odd, using
> (-PGC_count_mask & PGC_count_mask) would probably be an
> acceptable replacement here and further down.

(-PGC_count_mask & PGC_count_mask) is always 0.

I guess you mean:

if ( page->count_info & ~(PGC_count_mask | PGC_allocated) )

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