Re: [Xen-devel] [PATCH 24/27] xen/arm: page: Describe the layout of flags used to update page tables

[Julien Grall <julien.grall@xxxxxxx>]

On 08/23/2017 03:08 PM, Andre Przywara wrote:
> Hi,
>
> On 14/08/17 15:24, Julien Grall wrote:
> > Currently, the flags used to update page tables (i.e PAGE_HYPERVISOR_*)
> > only contains the memory attribute index. Follow-up patches will add
> > more information in it.
> >
> > At the same time introduce PAGE_AI_MASK to get the memory attribute
> > index easily.
> >
> > Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> I wonder if that should be merged with the next patch, to explain the
> reason for it. As it stands now it just applies a mask to some existing
> call, which looks a bit suspicious.
> But that's just a nit and the patch itself is fine, so:
Not really it just documents the current behavior rather than hiding 
what is going on.
Cheers,

> Reviewed-by: Andre Przywara <andre.przywara@xxxxxxx>
>
> Cheers,
> Andre.
>
> > ---
> >   xen/arch/arm/mm.c          | 2 +-
> >   xen/include/asm-arm/page.h | 7 +++++++
> >   2 files changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> > index 411fe02842..cd7bcf7aca 100644
> > --- a/xen/arch/arm/mm.c
> > +++ b/xen/arch/arm/mm.c
> > @@ -1021,7 +1021,7 @@ static int create_xen_entries(enum xenmap_operation op,
> >                   }
> >                   if ( op == RESERVE )
> >                       break;
> > -                pte = mfn_to_xen_entry(mfn, flags);
> > +                pte = mfn_to_xen_entry(mfn, PAGE_AI_MASK(flags));
> >                   pte.pt.table = 1;
> >                   write_pte(entry, pte);
> >                   break;
> > diff --git a/xen/include/asm-arm/page.h b/xen/include/asm-arm/page.h
> > index d9dac92e73..1bf8e9d012 100644
> > --- a/xen/include/asm-arm/page.h
> > +++ b/xen/include/asm-arm/page.h
> > @@ -63,6 +63,13 @@
> >   #define MAIR0VAL (MAIRVAL & 0xffffffff)
> >   #define MAIR1VAL (MAIRVAL >> 32)
> >   
> > +/*
> > + * Layout of the flags used for updating the hypervisor page tables
> > + *
> > + * [0:2] Memory Attribute Index
> > + */
> > +#define PAGE_AI_MASK(x) ((x) & 0x7U)
> > +
> >   #define PAGE_HYPERVISOR         (MT_NORMAL)
> >   #define PAGE_HYPERVISOR_NOCACHE (MT_DEVICE_nGnRE)
> >   #define PAGE_HYPERVISOR_WC      (MT_NORMAL_NC)
--
Julien Grall

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