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

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>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 85692c9..977a542 100644 (file)
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1370,7 +1370,7 @@ 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 */
 }