KVM: X86: Implement userspace interface to set virtual_tsc_khz

This patch implements two new vm-ioctls to get and set the
virtual_tsc_khz if the machine supports tsc-scaling. Setting
the tsc-frequency is only possible before userspace creates
any vcpu.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

2 files changed, 55 insertions, 0 deletions

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 8c4549bef4e..a9887376243 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -64,6 +64,8 @@ MODULE_LICENSE("GPL");
 #define DEBUGCTL_RESERVED_BITS (~(0x3fULL))
 
 #define TSC_RATIO_RSVD          0xffffff0000000000ULL
+#define TSC_RATIO_MIN		0x0000000000000001ULL
+#define TSC_RATIO_MAX		0x000000ffffffffffULL
 
 static bool erratum_383_found __read_mostly;
 
@@ -189,6 +191,7 @@ static int nested_svm_intercept(struct vcpu_svm *svm);
 static int nested_svm_vmexit(struct vcpu_svm *svm);
 static int nested_svm_check_exception(struct vcpu_svm *svm, unsigned nr,
 				      bool has_error_code, u32 error_code);
+static u64 __scale_tsc(u64 ratio, u64 tsc);
 
 enum {
 	VMCB_INTERCEPTS, /* Intercept vectors, TSC offset,
@@ -798,6 +801,23 @@ static __init int svm_hardware_setup(void)
 	if (boot_cpu_has(X86_FEATURE_FXSR_OPT))
 		kvm_enable_efer_bits(EFER_FFXSR);
 
+	if (boot_cpu_has(X86_FEATURE_TSCRATEMSR)) {
+		u64 max;
+
+		kvm_has_tsc_control = true;
+
+		/*
+		 * Make sure the user can only configure tsc_khz values that
+		 * fit into a signed integer.
+		 * A min value is not calculated needed because it will always
+		 * be 1 on all machines and a value of 0 is used to disable
+		 * tsc-scaling for the vcpu.
+		 */
+		max = min(0x7fffffffULL, __scale_tsc(tsc_khz, TSC_RATIO_MAX));
+
+		kvm_max_guest_tsc_khz = max;
+	}
+
 	if (nested) {
 		printk(KERN_INFO "kvm: Nested Virtualization enabled\n");
 		kvm_enable_efer_bits(EFER_SVME | EFER_LMSLE);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 579ce34e790..1d5a7f41879 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -87,6 +87,11 @@ EXPORT_SYMBOL_GPL(kvm_x86_ops);
 int ignore_msrs = 0;
 module_param_named(ignore_msrs, ignore_msrs, bool, S_IRUGO | S_IWUSR);
 
+bool kvm_has_tsc_control;
+EXPORT_SYMBOL_GPL(kvm_has_tsc_control);
+u32  kvm_max_guest_tsc_khz;
+EXPORT_SYMBOL_GPL(kvm_max_guest_tsc_khz);
+
 #define KVM_NR_SHARED_MSRS 16
 
 struct kvm_shared_msrs_global {
@@ -1986,6 +1991,7 @@ int kvm_dev_ioctl_check_extension(long ext)
 	case KVM_CAP_X86_ROBUST_SINGLESTEP:
 	case KVM_CAP_XSAVE:
 	case KVM_CAP_ASYNC_PF:
+	case KVM_CAP_GET_TSC_KHZ:
 		r = 1;
 		break;
 	case KVM_CAP_COALESCED_MMIO:
@@ -2012,6 +2018,9 @@ int kvm_dev_ioctl_check_extension(long ext)
 	case KVM_CAP_XCRS:
 		r = cpu_has_xsave;
 		break;
+	case KVM_CAP_TSC_CONTROL:
+		r = kvm_has_tsc_control;
+		break;
 	default:
 		r = 0;
 		break;
@@ -3045,6 +3054,32 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 		r = kvm_vcpu_ioctl_x86_set_xcrs(vcpu, u.xcrs);
 		break;
 	}
+	case KVM_SET_TSC_KHZ: {
+		u32 user_tsc_khz;
+
+		r = -EINVAL;
+		if (!kvm_has_tsc_control)
+			break;
+
+		user_tsc_khz = (u32)arg;
+
+		if (user_tsc_khz >= kvm_max_guest_tsc_khz)
+			goto out;
+
+		kvm_x86_ops->set_tsc_khz(vcpu, user_tsc_khz);
+
+		r = 0;
+		goto out;
+	}
+	case KVM_GET_TSC_KHZ: {
+		r = -EIO;
+		if (check_tsc_unstable())
+			goto out;
+
+		r = vcpu_tsc_khz(vcpu);
+
+		goto out;
+	}
 	default:
 		r = -EINVAL;
 	}