Re: [PATCH] x86: Construct 32 bit boot time page tables in native format.

Rafael J. Wysocki
2008-01-25T22:05:30Z

On Friday, 25 of January 2008, Pavel Machek wrote:
> On Thu 2008-01-24 16:27:58, H. Peter Anvin wrote:
> > Pavel Machek wrote:
> > >>>
> > >>I just looked at the ACPI suspend code, and it looks
> > >>like it hacks its own identity map at runtime. Pavel,
> > >>am I reading that code right?
> > >
> > >Yes, I think so, I believe we do it on both 32 and 64
> > >bit now.
> > >
> >
> > So the background to this... we need an identity map to
> > trampoline at early boot, obviously, but we'd like it to
> > not stick around more than necessary. We have
> > zap_low_mappings() now but it's not really sufficient.
> >
> > Secondary SMP processors need these mappings during
> > trampolining -- presumably including CPU hotplug -- and
> > I'm suspecting it might simply make sense to use a
> > separate set of page tables (with both the identity and
> > the kernel map) for trampolining and just keep them
> > around. That way they would be usable for ACPI as well.
>
> That would enable some cleanups, yes.

Speaking of cleanups, the following one is applicable IMO.

Greetings,
Rafael

---
arch/x86/mm/init_32.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

Index: linux-2.6/arch/x86/mm/init_32.c
===================================================================
--- linux-2.6.orig/arch/x86/mm/init_32.c
+++ linux-2.6/arch/x86/mm/init_32.c
@@ -444,23 +444,23 @@ static void __init pagetable_init (void)
paravirt_pagetable_setup_done(pgd_base);
}

-#if defined(CONFIG_HIBERNATION) || defined(CONFIG_ACPI)
+#ifdef CONFIG_SUSPEND
/*
* Swap suspend & friends need this for resume because things like the intel-agp
* driver might have split up a kernel 4MB mapping.
*/
-char __nosavedata swsusp_pg_dir[PAGE_SIZE]
+char swsusp_pg_dir[PAGE_SIZE]
__attribute__ ((aligned (PAGE_SIZE)));

static inline void save_pg_dir(void)
{
memcpy(swsusp_pg_dir, swapper_pg_dir, PAGE_SIZE);
}
-#else
+#else /* !CONFIG_SUSPEND */
static inline void save_pg_dir(void)
{
}
-#endif
+#endif /* !CONFIG_SUSPEND */

void zap_low_mappings (void)
{