[PATCH v2 4/5] x86/kvm: Add MSR_KVM_PREEMPT_COUNT guest support

Wanpeng Li
2022-04-01T08:11:55Z

The x86 guest passes the per-cpu preempt_count value to the hypervisor,
so the hypervisor knows whether the guest is running in the critical
section.

Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
arch/x86/kernel/kvm.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 79e0b8d63ffa..5b900334de6e 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -366,6 +366,14 @@ static void kvm_guest_cpu_init(void)

if (has_steal_clock)
kvm_register_steal_time();
+
+ if (kvm_para_has_feature(KVM_FEATURE_PREEMPT_COUNT)) {
+ u64 pa = slow_virt_to_phys(this_cpu_ptr(&__preempt_count))
+ | KVM_MSR_ENABLED;
+ wrmsrl(MSR_KVM_PREEMPT_COUNT, pa);
+
+ pr_debug("setup pv preempt_count: cpu %d\n", smp_processor_id());
+ }
}

static void kvm_pv_disable_apf(void)
@@ -442,6 +450,8 @@ static void kvm_guest_cpu_offline(bool shutdown)
if (!shutdown)
apf_task_wake_all();
kvmclock_disable();
+ if (kvm_para_has_feature(KVM_FEATURE_PREEMPT_COUNT))
+ wrmsrl(MSR_KVM_PREEMPT_COUNT, 0);
}

static int kvm_cpu_online(unsigned int cpu)
--
2.25.1