Re: [Xen-devel] [PATCH v1] xen/arm: Do not allocate pte entries for MAP_SMALL_PAGES

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Ian,

On 03/03/2015 10:27, Ian Campbell wrote:
> On Tue, 2015-03-03 at 13:28 +0530, Vijay Kilari wrote:
> > On Tue, Feb 24, 2015 at 6:29 PM, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
> > > On 24/02/15 10:26, Ian Campbell wrote:
> > > > On Tue, 2015-02-24 at 09:38 +0000, Julien Grall wrote:
> > > > > Hi Ian,
> > > > >
> > > > > On 24/02/2015 09:31, Ian Campbell wrote:
> > > > > > On Wed, 2015-02-18 at 13:03 +0000, Julien Grall wrote:
> > > > > > > > +                {
> > > > > > > > +                    pte = mfn_to_xen_entry(mfn, (ai & 0xffff));
> > > > > > > Please introduce a new macro for the mask.
> > > > > > Better would be a pte_foo accessor, similar (if not identical) to x86's
> > > > > > pte_get_flags. So pte_get_flags(ai) or so.
> > > > > I'm not able to find a such function in x86. Did you intend to mean
> > > > > pte_flags_to_cacheattr?
> > > > It's actually get_pte_flags.
> > > >
> > > > > In another side, using PTE_PRESENT would require to introduce a
> > > > > PAGE_AVAIL0 (or smth similar).
> > > > Why?
> > > If we have only a bit PTE_PRESENT, how do you define MAP_SMALL_PAGES?
> > MAP_SMALL_PAGES is already defined as WRITE_ALLOC which occupies lower 3 bits
> > what is need for PAGE_AVAIL0?
> >
> > Below definitions should suffice?
> I think so. You don't need the ()s around DEV_* and WRITE_ALLOC etc in
> the PAGE_* definitions.
I'm not sure to follow here. Do you think MAP_SMALL_PAGES should be 
defined as WRITE_ALLOC?

> A comment on the format of the bit packing done here would also be
> useful e.g. "16: present\n2:0: pte attributes field" in a little block
> comment above this stuff, below the DEV_* stuff.
>
> PAGE_PRESENT might be more in keepign that PTE_PRESENT, since this isn't
> a PTE bit pattern.
Sounds good to me.

Regards,

--
Julien Grall

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