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Subject[patch 044/104] xen: do not reserve 2 pages of padding between hypervisor and fixmap.
2.6.27-stable review patch.  If anyone has any objections, please let us know.

From: Ian Campbell <>

commit 5dc64a3442b98eaa0e3730c35fcf00cf962a93e7 upstream.

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 <>
Signed-off-by: Ingo Molnar <>
Cc: Jeremy Fitzhardinge <>
Signed-off-by: Greg Kroah-Hartman <>

arch/x86/xen/enlighten.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1413,7 +1413,7 @@ 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 */

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