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SubjectRFC: x86: cap iomem_resource to addressable physical memory
x86 cannot generate full 64-bit addresses; this patch clamps iomem
addresses to the accessible range.

I wanted to post it for review before committing it, however; comments
would be appreciated, especially of the kind "this is done too early/too
late/in the wrong place/incorrectly".

From 8dd8d59d1d1586b350401d6a5f8c7a9e30f142d4 Mon Sep 17 00:00:00 2001
From: H. Peter Anvin <>
Date: Tue, 9 Jun 2009 18:20:39 -0700
Subject: [PATCH] x86: cap iomem_resource to addressable physical memory

iomem_resource is by default initialized to -1, which means 64 bits of
physical address space if 64-bit resources are enabled. However, x86
CPUs cannot address 64 bits of physical address space. Thus, we want
to cap the physical address space to what the union of all CPU can
actually address.

Without this patch, we may end up assigning inaccessible values to
uninitialized 64-bit PCI memory resources.

Signed-off-by: H. Peter Anvin <>
Cc: Matthew Wilcox <>
Cc: Jesse Barnes <>
Cc: Martin Mares <>
arch/x86/kernel/cpu/common.c | 3 +++
1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 77848d9..de8a49c 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -839,6 +839,9 @@ static void __cpuinit identify_cpu(struct cpuinfo_x86 *c)
#if defined(CONFIG_NUMA) && defined(CONFIG_X86_64)
+ /* Cap the iomem address space to what is addressable on all CPUs */
+ iomem_resource.end &= (1ULL << c->x86_phys_bits) - 1;

#ifdef CONFIG_X86_64
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