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

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

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?

> > #define PTE_PRESENT ((struct lpae_t){ .pt.present = 1 }).bits
> >
> > probably doesn't work, I'm not even sure if this sort of thing is
> > possible. If not then "#define PTE_PRESET (1ULL<<0)".
> 
> The attribute index (write-alloc, buferrable...) is using the less 
> significant 3 bits. So I was suggesting to use the top of the word.

I was suggesting to use bits 2..4 as in the real PTE, to be more similar
to the x86 interpretation of this argument.

Ian.


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