For F17h AMD CPUs, the CPB capability 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]
cpuhp_invoke_callback+0x86/0x560
sort_range+0x20/0x20
cpuhp_thread_fun+0xb0/0x110
smpboot_thread_fn+0xef/0x160
kthread+0x113/0x130
kthread_create_worker_on_cpu+0x70/0x70
ret_from_fork+0x35/0x40
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 <fllin...@amazon.com>
Fixes: 0237199186e7 ("x86/CPU/AMD: Set the CPB bit unconditionally on F17h")
---
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 fb6a64bd765f..ee4d79fa1b19 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -823,8 +823,11 @@ 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);
}
--
2.17.2
