Re: [Xen-devel] [PATCH v4] boot allocator: Use arch helper for virt_to_mfn on DIRECTMAP

[Julien Grall <julien.grall@xxxxxxx>]

On 04/04/2017 06:50 AM, Vijay Kilari wrote:
> Hi Julien,
Hello Vijay,

> On Mon, Apr 3, 2017 at 3:31 PM, Julien Grall <julien.grall@xxxxxxx> wrote:
> > On 28/03/17 13:35, vijay.kilari@xxxxxxxxx wrote:
> > > diff --git a/xen/include/asm-arm/arm32/mm.h
> > > b/xen/include/asm-arm/arm32/mm.h
> > > new file mode 100644
> > > index 0000000..e93d9df
> > > --- /dev/null
> > > +++ b/xen/include/asm-arm/arm32/mm.h
> > > @@ -0,0 +1,20 @@
> > > +#ifndef __ARM_ARM32_MM_H__
> > > +#define __ARM_ARM32_MM_H__
> > > +
> > > +/* On ARM only xenheap memory is directly mapped. Hence return false. */
> >
> > By reading this comment some people will wonder why you don't check whether
> > the mfn is in xenheap then. As mentioned above, I am ok if you always return
> > false here. But you need to explain why.
> Is this ok?
>
> "On ARM32, all the RAM is not mapped by Xen, instead it is mapped by xenheap.
> So DIRECTMAP_VIRT region is not mapped.
> Hence we return always false when mfn is checked on DIRECTMAP_VIRT region."
This does not make any sense. You don't map the RAM using xenheap, 
xenheap is the only portion of the RAM always mapped. Furthermore, as I 
said there are no "DIRECTMAP_VIRT" region on ARM, have a grep at this 
keyword for ARM32...
How about:

"Only a limited amount of RAM, called xenheap, is always mapped on 
ARM32. For convenience always return false."
Cheers,

--
Julien Grall

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