Re: [PATCH v2 22/23] x86: make Xen early boot code relocatable

["Jan Beulich" <JBeulich@suse.com>]

>>> On 14.08.15 at 13:52, <daniel.kiper@oracle.com> wrote:
> On Tue, Aug 11, 2015 at 12:48:06PM -0400, Konrad Rzeszutek Wilk wrote:
>> On Mon, Jul 20, 2015 at 04:29:17PM +0200, Daniel Kiper wrote:
>> > diff --git a/xen/include/asm-x86/page.h b/xen/include/asm-x86/page.h
>> > index 87b3341..27481ac 100644
>> > --- a/xen/include/asm-x86/page.h
>> > +++ b/xen/include/asm-x86/page.h
>> > @@ -283,7 +283,7 @@ extern root_pgentry_t idle_pg_table[ROOT_PAGETABLE_ENTRIES];
>> >  extern l2_pgentry_t  *compat_idle_pg_table_l2;
>> >  extern unsigned int   m2p_compat_vstart;
>> >  extern l2_pgentry_t l2_xenmap[L2_PAGETABLE_ENTRIES],
>> > -    l2_bootmap[L2_PAGETABLE_ENTRIES];
>> > +    l2_bootmap[4*L2_PAGETABLE_ENTRIES];
>>
>> ? Why do we need to expand this to be 16kB?
> 
> TBH, we need 8 KiB in the worst case. The worst case is when
> next GiB starts (e.g. 1 GiB ends and 2 GiB starts) in the middle
> of Xen image. In this situation we must hook up lower l2_bootmap
> table with lower l3_bootmap entry, higher l2_bootmap table with
> higher l3_bootmap entry and finally fill l2_bootmap relevant
> tables in proper way. Sadly, this method requires more calculations.
> To avoid that I have added 3 l2_bootmap tables and simply hook up
> one after another with relevant l3_bootmap entries. However, if
> you wish we can reduce number of l2_bootmap tables to two. This
> way code will be more complicated but we will save about 8 KiB.

Wouldn't it be better (simpler) to enforce, say, 16Mb alignment
in the PE32+ header (which the EFI loader would then honor)?

Jan