From 42d9cedf21ba07085041566a9d6e99533fd20bda Mon Sep 17 00:00:00 2001
From: "H. Peter Anvin" <hpa@linux.intel.com>
Date: Wed, 16 May 2012 13:22:41 -0700
Subject: [PATCH] --- yaml --- r: 309166 b: refs/heads/master c:
 796038799a72adb279d785c9154df6eeb98b6e8d h: refs/heads/master v: v3

---
 [refs]                           |  2 +-
 trunk/arch/x86/kernel/realmode.c | 11 ++++++++---
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/[refs] b/[refs]
index 7da9a8aaa8db..96f2371c8ecf 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 34d0b02e08470c56a411ba6da1f377bc6da02826
+refs/heads/master: 796038799a72adb279d785c9154df6eeb98b6e8d
diff --git a/trunk/arch/x86/kernel/realmode.c b/trunk/arch/x86/kernel/realmode.c
index 66ac276cf361..099277984b80 100644
--- a/trunk/arch/x86/kernel/realmode.c
+++ b/trunk/arch/x86/kernel/realmode.c
@@ -22,6 +22,7 @@ void __init setup_real_mode(void)
 	size_t size = PAGE_ALIGN(real_mode_blob_end - real_mode_blob);
 #ifdef CONFIG_X86_64
 	u64 *trampoline_pgd;
+	u32 efer_low, efer_high;
 #endif
 
 	/* Has to be in very low memory so we can execute real-mode AP code. */
@@ -65,9 +66,13 @@ void __init setup_real_mode(void)
 	trampoline_header->gdt_limit = __BOOT_DS + 7;
 	trampoline_header->gdt_base = __pa(boot_gdt);
 #else
-	if (rdmsr_safe(MSR_EFER, &trampoline_header->efer_low,
-		       &trampoline_header->efer_high))
-		BUG();
+	/*
+	 * Some AMD processors will #GP(0) if EFER.LMA is set in WRMSR
+	 * so we need to mask it out.
+	 */
+	rdmsr(MSR_EFER, efer_low, efer_high);
+	trampoline_header->efer_low  = efer_low & ~EFER_LMA;
+	trampoline_header->efer_high = efer_high;
 
 	trampoline_header->start = (u64) secondary_startup_64;
 	trampoline_cr4_features = &trampoline_header->cr4;