path: root/init
diff options
authorThomas Gleixner <>2016-12-09 19:29:10 +0100
committerThomas Gleixner <>2016-12-09 21:23:21 +0100
commite7ff3a47630d9512d0bcbdfa73660021087ba445 (patch)
treef9628f32e5539f1d275c5529168fd2dc8e9f1231 /init
parent3344ed30791af66dbbad5f375008f3d1863b6c99 (diff)
x86/amd: Check for the C1E bug post ACPI subsystem init
AMD CPUs affected by the E400 erratum suffer from the issue that the local APIC timer stops when the CPU goes into C1E. Unfortunately there is no way to detect the affected CPUs on early boot. It's only possible to determine the range of possibly affected CPUs from the family/model range. The actual decision whether to enter C1E and thus cause the bug is done by the firmware and we need to detect that case late, after ACPI has been initialized. The current solution is to check in the idle routine whether the CPU is affected by reading the MSR_K8_INT_PENDING_MSG MSR and checking for the K8_INTP_C1E_ACTIVE_MASK bits. If one of the bits is set then the CPU is affected and the system is switched into forced broadcast mode. This is ineffective and on non-affected CPUs every entry to idle does the extra RDMSR. After doing some research it turns out that the bits are visible on the boot CPU right after the ACPI subsystem is initialized in the early boot process. So instead of polling for the bits in the idle loop, add a detection function after acpi_subsystem_init() and check for the MSR bits. If set, then the X86_BUG_AMD_APIC_C1E is set on the boot CPU and the TSC is marked unstable when X86_FEATURE_NONSTOP_TSC is not set as it will stop in C1E state as well. The switch to broadcast mode cannot be done at this point because the boot CPU still uses HPET as a clockevent device and the local APIC timer is not yet calibrated and installed. The switch to broadcast mode on the affected CPUs needs to be done when the local APIC timer is actually set up. This allows to cleanup the amd_e400_idle() function in the next step. Signed-off-by: Thomas Gleixner <> Signed-off-by: Borislav Petkov <> Cc: Jiri Olsa <> Link: Signed-off-by: Thomas Gleixner <>
Diffstat (limited to 'init')
1 files changed, 3 insertions, 0 deletions
diff --git a/init/main.c b/init/main.c
index 2858be7..1d7038c 100644
--- a/init/main.c
+++ b/init/main.c
@@ -448,6 +448,8 @@ void __init parse_early_param(void)
done = 1;
+void __init __weak arch_post_acpi_subsys_init(void) { }
void __init __weak smp_setup_processor_id(void)
@@ -649,6 +651,7 @@ asmlinkage __visible void __init start_kernel(void)
+ arch_post_acpi_subsys_init();
if (efi_enabled(EFI_RUNTIME_SERVICES)) {