kvm_x86_ops->vcpu_put(vcpu);
vcpu->arch.last_host_tsc = rdtsc();
/*
- * If userspace has set any breakpoints or watchpoints, dr6 is restored
- * on every vmexit, but if not, we might have a stale dr6 from the
- * guest. do_debug expects dr6 to be cleared after it runs, do the same.
+ * Here dr6 is either zero or, if the guest has run and userspace
+ * has not set any breakpoints or watchpoints, it can be set to
+ * the guest dr6 (stored in vcpu->arch.dr6). do_debug expects dr6
+ * to be cleared after it runs, so clear the host register. However,
+ * MOV to DR can be expensive when running nested, omit it if
+ * vcpu->arch.dr6 is already zero: in that case, the host dr6 cannot
+ * currently be nonzero.
*/
- set_debugreg(0, 6);
+ if (vcpu->arch.dr6)
+ set_debugreg(0, 6);
}
static int kvm_vcpu_ioctl_get_lapic(struct kvm_vcpu *vcpu,