From: Jan Stancek jstancek@redhat.com
mainline inclusion from mainline-v5.3 commit afa8b475c1ae category: bugfix bugzilla: 17251 CVE: NA
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KVM guests with commit c8c4076723da ("x86/timer: Skip PIT initialization on modern chipsets") applied to guest kernel have been observed to have unusually higher CPU usage with symptoms of increase in vm exits for HLT and MSW_WRITE (MSR_IA32_TSCDEADLINE).
This is caused by older QEMUs lacking support for X86_FEATURE_ARAT. lapic clock retains CLOCK_EVT_FEAT_C3STOP and nohz stays inactive. There's no usable broadcast device either.
Do the PIT initialization if guest CPU lacks X86_FEATURE_ARAT. On real hardware it shouldn't matter as ARAT and DEADLINE come together.
Fixes: c8c4076723da ("x86/timer: Skip PIT initialization on modern chipsets") Signed-off-by: Jan Stancek jstancek@redhat.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Xiongfeng Wang wangxiongfeng2@huawei.com Reviewed-by: Hanjun Guo guohanjun@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- arch/x86/kernel/apic/apic.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c index 8fe688e..14c957b 100644 --- a/arch/x86/kernel/apic/apic.c +++ b/arch/x86/kernel/apic/apic.c @@ -836,6 +836,10 @@ bool __init apic_needs_pit(void) apic_intr_mode == APIC_VIRTUAL_WIRE_NO_CONFIG) return true;
+ /* Virt guests may lack ARAT, but still have DEADLINE */ + if (!boot_cpu_has(X86_FEATURE_ARAT)) + return true; + /* Deadline timer is based on TSC so no further PIT action required */ if (boot_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER)) return false;