Re: [Xen-devel] new domain builder breaks compatibility

[John Levon <levon@xxxxxxxxxxxxxxxxx>]

On Thu, Feb 01, 2007 at 04:15:16PM +0100, Gerd Hoffmann wrote:

> > Does that ensure the 4Mb alignment too?
> 
> Yes.  Uhm, no, depends.  It completely fills the topmost L1 pagetable
> with entries, so you end up with an 4MB alignment for 32bit and 2MB
> alignment for PAE and 64bit.  I think the old builder had the same
> behaviour, so the 4MB are actually a documentation bug ;)

Hmm... am I misunderstanding this code:

 816         /* v_end = (vstack_end + (1UL<<22)-1) & ~((1UL<<22)-1); */
 817         v_end = vstack_end;
 818         if ( !increment_ulong(&v_end, (1UL<<22)-1) )
 819             goto error_out;
 820         v_end &= ~((1UL<<22)-1);
 821
 822         if ( (v_end - vstack_end) < (512UL << 10) )
 823         {
 824             /* Add extra 4MB to get >= 512kB padding. */
 825             if ( !increment_ulong(&v_end, 1UL << 22) )
 826                 goto error_out;
 827         }

Surely that guarantees we get at least 512Kb and it ends on a 4Mb
boundary?

regards
john

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