From: Paolo Bonzini <pbonzini@redhat.com>
Date: Mon, 1 Feb 2010 12:03:05 -0500
Subject: [x86] fix AMD M-C boot inside xen on pre-5.5 hypervisor
Message-id: <1265025785-32255-1-git-send-email-pbonzini@redhat.com>
Patchwork-id: 23011
O-Subject: [RHEL5.5 PATCH v2] x86: Fix AMD Magny-Cours boot inside xen on
	pre-5.5 hypervisor
Bugzilla: 560013
RH-Acked-by: Andrew Jones <drjones@redhat.com>
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
RH-Acked-by: Don Dutile <ddutile@redhat.com>

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=560013

Upstream: not present (see below)

Brew build: https://brewweb.devel.redhat.com/taskinfo?taskID=2235184

This patch checks for the presence of an AMD NorthBridge before accessing
the NodeID MSR.

Checking for the NorthBridge this way was considered hackish and so it
was applied only to 5.4.z.  For 5.5 a hypervisor fix was used instead,
which masked to guests the presence of the MSR.  Unfortunately, the two
patches fix two different scenarios.  Patching the hypervisor fixes
non-Magny-Cours-aware guests; instead, patching the kernel lets the
system boot even on non-Magny-Cours-aware hypervisors.

This is because while the code already looks for the presence of the
MSR in CPUID, when the hypervisor is not from RHEL 5.5 as well Xen
will set the NodeIDMSR bit and still inject a #GP on the corresponding
rdmsr.  So now there is a regression in that if the hypervisor is kept
to 5.4, 5.4.z will boot but 5.5 won't.

This patch fixes the bug by adding the kernel workaround to 5.5 as well.
It is the same as 5.4.z except for context.  Tested by me on amd-dinar-03.

Upstream doesn't care so much about upgrade scenarios, and Magny-Cours
systems are very very new, so I didn't post the patch there.

v1->v2: fix typo

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Andrew Jones <drjones@redhat.com>

diff --git a/arch/i386/kernel/cpu/amd.c b/arch/i386/kernel/cpu/amd.c
index b4c1d47..c201a15 100644
--- a/arch/i386/kernel/cpu/amd.c
+++ b/arch/i386/kernel/cpu/amd.c
@@ -4,6 +4,7 @@
 #include <asm/io.h>
 #include <asm/processor.h>
 #include <asm/pci-direct.h>
+#include <asm/k8.h>
 
 #include "cpu.h"
 
@@ -43,6 +44,12 @@ static void __cpuinit amd_fixup_dcm(struct cpuinfo_x86 *c)
 	if (cpu_has(c, X86_FEATURE_AMD_DCM))
 		return;
 
+	/* proceed only if there is a valid AMD northbridge
+	 * (not in virtualized environments!)
+	 */
+	if (!early_is_k8_nb(read_pci_config(0, 24, 3, 0x00)))
+		return;
+
 	rdmsrl(0xc001100c, value);
 
 	nodes = ((value >> 3) & 7) + 1;
diff --git a/arch/x86_64/kernel/setup.c b/arch/x86_64/kernel/setup.c
index dacb23a..ad74550 100644
--- a/arch/x86_64/kernel/setup.c
+++ b/arch/x86_64/kernel/setup.c
@@ -69,6 +69,7 @@
 #include <asm/generic-hypervisor.h>
 #include <asm/pci-direct.h>
 #include <asm/kvm_para.h>
+#include <asm/k8.h>
 
 /*
  * Machine setup..
@@ -823,6 +824,12 @@ static void __cpuinit amd_fixup_dcm(struct cpuinfo_x86 *c)
 	if (cpu_has(c, X86_FEATURE_AMD_DCM))
 		return;
 
+	/* proceed only if there is a valid AMD northbridge
+	 * (not in virtualized environments!)
+	 */
+	if (!early_is_k8_nb(read_pci_config(0, 24, 3, 0x00)))
+		return;
+
 	rdmsrl(0xc001100c, value);
 
 	nodes = ((value >> 3) & 7) + 1;