[PATCH AUTOSEL 4.9 04/20] x86/CPU/AMD: Don't force the CPB cap when running under a hypervisor

From: Sasha Levin
Date: Sat Jun 08 2019 - 07:55:21 EST

From: Frank van der Linden <fllinden@xxxxxxxxxx>

[ Upstream commit 2ac44ab608705948564791ce1d15d43ba81a1e38 ]

For F17h AMD CPUs, the CPB capability ('Core Performance Boost') is forcibly set,
because some versions of that chip incorrectly report that they do not have it.

However, a hypervisor may filter out the CPB capability, for good
reasons. For example, KVM currently does not emulate setting the CPB
bit in MSR_K7_HWCR, and unchecked MSR access errors will be thrown
when trying to set it as a guest:

unchecked MSR access error: WRMSR to 0xc0010015 (tried to write 0x0000000001000011) at rIP: 0xffffffff890638f4 (native_write_msr+0x4/0x20)

Call Trace:
boost_set_msr+0x50/0x80 [acpi_cpufreq]

To avoid this issue, don't forcibly set the CPB capability for a CPU
when running under a hypervisor.

Signed-off-by: Frank van der Linden <fllinden@xxxxxxxxxx>
Acked-by: Borislav Petkov <bp@xxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: bp@xxxxxxxxx
Cc: jiaxun.yang@xxxxxxxxxxx
Fixes: 0237199186e7 ("x86/CPU/AMD: Set the CPB bit unconditionally on F17h")
Link: http://lkml.kernel.org/r/20190522221745.GA15789@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
[ Minor edits to the changelog. ]
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
arch/x86/kernel/cpu/amd.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index be6d0543e626..52a65f14db06 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -766,8 +766,11 @@ static void init_amd_zn(struct cpuinfo_x86 *c)
set_cpu_cap(c, X86_FEATURE_ZEN);

- /* Fix erratum 1076: CPB feature bit not being set in CPUID. */
- if (!cpu_has(c, X86_FEATURE_CPB))
+ /*
+ * Fix erratum 1076: CPB feature bit not being set in CPUID.
+ * Always set it, except when running under a hypervisor.
+ */
+ if (!cpu_has(c, X86_FEATURE_HYPERVISOR) && !cpu_has(c, X86_FEATURE_CPB))
set_cpu_cap(c, X86_FEATURE_CPB);