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

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Tue, 2015-03-03 at 11:17 +0000, Julien Grall wrote:
> 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?

Sorry I just meant that:
        +#define PAGE_HYPERVISOR_WC      ((DEV_WC) | PTE_PRESENT )
should be just:
        +#define PAGE_HYPERVISOR_WC      (DEV_WC | PTE_PRESENT )
etc, no need for the inner-()s.

MAP_SMALL_PAGES was correct as 
        +#define MAP_SMALL_PAGES         (WRITEALLOC)

Ian


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