[PATCH] xen: do not reserve 2 pages of padding between hypervisor and fixmap.

[PATCH] xen: do not reserve 2 pages of padding between hypervisor and fixmap.

[Ian Campbell]

When reserving space for the hypervisor the Xen paravirt backend adds
an extra two pages (this was carried forward from the 2.6.18-xen tree
which had them "for safety"). Depending on various CONFIG options this
can cause the boot time fixmaps to span multiple PMDs which is not
supported and triggers a WARN in early_ioremap_init().

This was exposed by 2216d199b1430d1c0affb1498a9ebdbd9c0de439 which
moved the dmi table parsing earlier.
    x86: fix CONFIG_X86_RESERVE_LOW_64K=y

    The bad_bios_dmi_table() quirk never triggered because we do DMI setup
    too late. Move it a bit earlier.

There is no real reason to reserve these two extra pages and the
fixmap already incorporates FIX_HOLE which serves the same
purpose. None of the other callers of reserve_top_address do this.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 arch/x86/xen/enlighten.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index bd6b50a..e8df41a 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1401,7 +1401,7 @@ static void __init xen_reserve_top(void)
 	if (HYPERVISOR_xen_version(XENVER_platform_parameters, &pp) == 0)
 		top = pp.virt_start;
 
-	reserve_top_address(-top + 2 * PAGE_SIZE);
+	reserve_top_address(-top);
 #endif	/* CONFIG_X86_32 */
 }
 
-- 
1.5.6.3

Re: [PATCH] xen: do not reserve 2 pages of padding between hypervisor and fixmap.

[Ingo Molnar]

* Ian Campbell <Ian.Campbell@citrix.com> wrote:

> When reserving space for the hypervisor the Xen paravirt backend adds 
> an extra two pages (this was carried forward from the 2.6.18-xen tree 
> which had them "for safety"). Depending on various CONFIG options this 
> can cause the boot time fixmaps to span multiple PMDs which is not 
> supported and triggers a WARN in early_ioremap_init().
> 
> This was exposed by 2216d199b1430d1c0affb1498a9ebdbd9c0de439 which
> moved the dmi table parsing earlier.
>     x86: fix CONFIG_X86_RESERVE_LOW_64K=y
> 
>     The bad_bios_dmi_table() quirk never triggered because we do DMI setup
>     too late. Move it a bit earlier.
> 
> There is no real reason to reserve these two extra pages and the
> fixmap already incorporates FIX_HOLE which serves the same
> purpose. None of the other callers of reserve_top_address do this.
> 
> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> Cc: Jeremy Fitzhardinge <jeremy@goop.org>
> Cc: Signed-off-by: Ingo Molnar <mingo@elte.hu>

applied to tip/x86/xen, thanks Ian!

	Ingo