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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.11.13 at 03:34, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> wrote:
> 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?

Yes, with the leading part getting cleared prior to the loop, and
the trailing part after (thus allowing to not re-initialized pl4e in
each loop's for()).

And the ending condition of course if off by one above: You
really want pl4e <= l4start + l4_table_offset(v_end - 1).

Jan


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