Re: [Xen-devel] [PATCH 2/2] xen/mm: Introduce PG_state_uninitialised

[Paul Durrant <xadimgnik@xxxxxxxxx>]

> -----Original Message-----
> From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of David 
> Woodhouse
> Sent: 17 March 2020 22:15
> To: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: sstabellini@xxxxxxxxxx; julien@xxxxxxx; wl@xxxxxxx; 
> konrad.wilk@xxxxxxxxxx;
> george.dunlap@xxxxxxxxxxxxx; andrew.cooper3@xxxxxxxxxx; 
> ian.jackson@xxxxxxxxxxxxx;
> george.dunlap@xxxxxxxxxx; jeff.kubascik@xxxxxxxxxxxxxxx; Xia, Hongyan 
> <hongyxia@xxxxxxxxxx>;
> stewart.hildebrand@xxxxxxxxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] [PATCH 2/2] xen/mm: Introduce PG_state_uninitialised
> 
> On Thu, 2020-02-20 at 12:59 +0100, Jan Beulich wrote:
> > On 07.02.2020 19:04, David Woodhouse wrote:
> > > --- a/xen/arch/x86/mm.c
> > > +++ b/xen/arch/x86/mm.c
> > > @@ -488,7 +488,8 @@ void share_xen_page_with_guest(struct page_info 
> > > *page, struct domain *d,
> > >
> > >      page_set_owner(page, d);
> > >      smp_wmb(); /* install valid domain ptr before updating refcnt. */
> > > -    ASSERT((page->count_info & ~PGC_xen_heap) == 0);
> > > +    ASSERT((page->count_info & ~PGC_xen_heap) == PGC_state_inuse ||
> > > +           (page->count_info & ~PGC_xen_heap) == 
> > > PGC_state_uninitialised);
> >
> > Can uninitialized pages really make it here?
> 
> Yep, we share the low 1MiB with dom_io.
> 

OOI anyone know why we do this? Is it actually necessary?

  Paul


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