Re: [Xen-devel] [V1 PATCH 06/11] PVH dom0: construct_dom0 changes

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Tue, 12 Nov 2013 16:35:05 +0000
"Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> >>> On 09.11.13 at 02:23, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
> >>> wrote:
......
> These look more complicated than necessary (largely due to the
> casts), but be it that way.
> 
> > +    pl4e = l4start + l4_table_offset(v_start);
> >...
> > +    *pl4e = l4e_from_pfn(get_gpfn_from_mfn(l4e_get_pfn(*pl4e)),
> > +                         l4e_get_flags(*pl4e));
> 
> But this one I told before needs to be in a loop. You must not make
> assumptions on guest virtual address space layout, and hence you
> must not assume none of the initial mapping crosses an L4 boundary.

Ah right, my bad.

> And once these are in a loop, getting the earlier two loops simplified
> (using l4e_empty() rather than plain memset()) and ordered properly
> (the head part before the main loop, the tail part after) will be
> almost obvious legibility cleanups.

Actually, the loop will go from v_start->L4 to v_end->L4. The memsets
are clearing the entries before v_start and after v_end. So, I'm
thinking something like:

clear entries before v_start using memset
clear entries after v_end using memset

for ( pl4e = l4start + l4_table_offset(v_start);
      pl4e <= l4start + l4_table_offset(v_end); 
      pl4e++)
{
    pl3e = map_l3t_from_l4e(*pl4e);
    for ( i = 0; i < PAGE_SIZE / sizeof(*pl3e); i++, pl3e++ )
    {
    ...
}

Look ok?

thanks,
Mukesh


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