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

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Fri, Aug 14, 2015 at 08:32:05AM -0600, Jan Beulich wrote:
> >>> On 14.08.15 at 15:59, <daniel.kiper@xxxxxxxxxx> wrote:
> > On Fri, Aug 14, 2015 at 06:49:18AM -0600, Jan Beulich wrote:
> >> >>> On 14.08.15 at 13:52, <daniel.kiper@xxxxxxxxxx> 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)?
> >
> > Good idea but then we must enforce this for multiboot protocol (v1 and v2)
> > too.
> > multiboot2 with my patches supports that solution. However, multiboot (v1)
> > could
> > be a bit problematic because it means that we must set load address to 16
> > MiB.
> > Are we sure that this region is available on all machines like region
> > starting
> > at 1 MiB?
>
> "This region" being which one?

16 MiB - 32 MiB.

Daniel

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel