Commit-ID: 52d3d06e706bdde3d6c5c386deb065c3b4c51618
Gitweb: http://git.kernel.org/tip/52d3d06e706bdde3d6c5c386deb065c3b4c51618
Author: Borislav Petkov <bp@xxxxxxx>
AuthorDate: Tue, 19 Feb 2013 19:33:12 +0100
Committer: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
CommitDate: Tue, 19 Feb 2013 10:44:00 -0800
x86, cpu, amd: Fix WC+ workaround for older virtual hosts
The WC+ workaround for F10h introduces a new MSR and kvm host #GPs
on accesses to unknown MSRs if paravirt is not compiled in. Use the
exception-handling MSR accessors so as not to break 3.8 and later guests
booting on older hosts.
Remove a redundant family check while at it.
Cc: Gleb Natapov <gleb@xxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Link: http://lkml.kernel.org/r/1361298793-31834-1-git-send-email-bp@xxxxxxxxx
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
---
arch/x86/kernel/cpu/amd.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 721ef32..163af4a 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -723,12 +723,14 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c)
* performance degradation for certain nested-paging guests.
* Prevent this conversion by clearing bit 24 in
* MSR_AMD64_BU_CFG2.
+ *
+ * NOTE: we want to use the _safe accessors so as not to #GP kvm
+ * guests on older kvm hosts.
*/
- if (c->x86 == 0x10) {
- rdmsrl(MSR_AMD64_BU_CFG2, value);
- value &= ~(1ULL << 24);
- wrmsrl(MSR_AMD64_BU_CFG2, value);
- }
+
+ rdmsrl_safe(MSR_AMD64_BU_CFG2, &value);
+ value &= ~(1ULL << 24);
+ wrmsrl_safe(MSR_AMD64_BU_CFG2, value);
}
rdmsr_safe(MSR_AMD64_PATCH_LEVEL, &c->microcode, &dummy);
--
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