Re: [Xen-devel] [PATCH 5/6] xen: arm: add some helpers for assessing p2m pte

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2014-06-10 at 12:54 +0100, Julien Grall wrote:
> On 06/10/2014 12:46 PM, Ian Campbell wrote:
> > On Tue, 2014-06-10 at 12:37 +0100, Julien Grall wrote:
> >> On 06/10/2014 10:57 AM, Ian Campbell wrote:
> >>>      mask = SECOND_MASK;
> >>>      second = map_domain_page(pte.p2m.base);
> >>>      pte = second[second_table_offset(paddr)];
> >>> -    if ( !pte.p2m.valid || !pte.p2m.table )
> >>> +    if ( !p2m_table(pte) )
> >>>          goto done;
> >>>  
> >>>      mask = THIRD_MASK;
> >>> @@ -156,11 +161,11 @@ paddr_t p2m_lookup(struct domain *d, paddr_t paddr, 
> >>> p2m_type_t *t)
> >>>      pte = third[third_table_offset(paddr)];
> >>>  
> >>>      /* This bit must be one in the level 3 entry */
> >>> -    if ( !pte.p2m.table )
> >>> +    if ( !p2m_table(pte) )
> >>>          pte.bits = 0;
> >>>  
> >>>  done:
> >>> -    if ( pte.p2m.valid )
> >>> +    if ( p2m_valid(pte) )
> >>
> >> Regardless the current check, I think this should be p2m_entry(pte) to
> >> help code comprehension.
> >>
> >> Indeed, the can only get the address if the pte is pointed to a memory
> >> block.
> > 
> > Yes, but an L3 PTE has the table bit set, which would make
> > p2m_entry(pte) false...
> 
> Hmmm... right. But this bit (ie table bit) doesn't have the same meaning
> on L3. Your comment on p2m_table is confusing.

You mean: /* Remember: L3 entries set the table bit! */ ?

That was intended to be a comment on the two helpers which follow. Do
you have an idea how I could make it clearer? Perhaps appending "So
these two functions will return the opposite to what you expect for L3
ptes"?

> 
> Anyway:
> 
> Acked-by: Julien Grall <julien.grall@xxxxxxxxxx>
> 

Thanks.



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