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

[Wanpeng Li <kernellwp@gmail.com>]

From: Wanpeng Li <wanpengli@tencent.com>

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 21933095a10e..e389fa4393ae 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