KVM: x86: Move TSC offset writes to common code

Also, ensure that the storing of the offset and the reading of the TSC
are never preempted by taking a spinlock.  While the lock is overkill
now, it is useful later in this patch series.

Signed-off-by: Zachary Amsden <zamsden@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8b0c51a1ada..886132b6ef1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -895,6 +895,22 @@ static void kvm_set_time_scale(uint32_t tsc_khz, struct pvclock_vcpu_time_info *
 
 static DEFINE_PER_CPU(unsigned long, cpu_tsc_khz);
 
+void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data)
+{
+        struct kvm *kvm = vcpu->kvm;
+        u64 offset;
+        unsigned long flags;
+
+        spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
+        offset = data - native_read_tsc();
+        kvm_x86_ops->write_tsc_offset(vcpu, offset);
+        spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags);
+
+        /* Reset of TSC must disable overshoot protection below */
+        vcpu->arch.hv_clock.tsc_timestamp = 0;
+}
+EXPORT_SYMBOL_GPL(kvm_write_tsc);
+
 static void kvm_write_guest_time(struct kvm_vcpu *v)
 {
         struct timespec ts;
@@ -5495,6 +5511,8 @@ struct  kvm *kvm_arch_create_vm(void)
         /* Reserve bit 0 of irq_sources_bitmap for userspace irq source */
         set_bit(KVM_USERSPACE_IRQ_SOURCE_ID, &kvm->arch.irq_sources_bitmap);
 
+        spin_lock_init(&kvm->arch.tsc_write_lock);
+
         return kvm;
 }