5 files changed, 71 insertions, 58 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 782d973b0719..ddebbe01fff9 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -422,10 +422,11 @@ struct kvm_vcpu_arch {
         u64 last_kernel_ns;
         u64 last_tsc_nsec;
         u64 last_tsc_write;
-        u32 virtual_tsc_khz;
         bool tsc_catchup;
-        u32  tsc_catchup_mult;
-        s8   tsc_catchup_shift;
+        bool tsc_always_catchup;
+        s8 virtual_tsc_shift;
+        u32 virtual_tsc_mult;
+        u32 virtual_tsc_khz;
 
         atomic_t nmi_queued;  /* unprocessed asynchronous NMIs */
         unsigned nmi_pending; /* NMI queued after currently running handler */
@@ -651,7 +652,7 @@ struct kvm_x86_ops {
 
         bool (*has_wbinvd_exit)(void);
 
-        void (*set_tsc_khz)(struct kvm_vcpu *vcpu, u32 user_tsc_khz);
+        void (*set_tsc_khz)(struct kvm_vcpu *vcpu, u32 user_tsc_khz, bool scale);
         void (*write_tsc_offset)(struct kvm_vcpu *vcpu, u64 offset);
 
         u64 (*compute_tsc_offset)(struct kvm_vcpu *vcpu, u64 target_tsc);
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 3ee1d83c695d..72975f758c83 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -731,7 +731,7 @@ static void start_apic_timer(struct kvm_lapic *apic)
                 u64 guest_tsc, tscdeadline = apic->lapic_timer.tscdeadline;
                 u64 ns = 0;
                 struct kvm_vcpu *vcpu = apic->vcpu;
-                unsigned long this_tsc_khz = vcpu_tsc_khz(vcpu);
+                unsigned long this_tsc_khz = vcpu->arch.virtual_tsc_khz;
                 unsigned long flags;
 
                 if (unlikely(!tscdeadline || !this_tsc_khz))
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 7bbd17cc3488..e12026e5244e 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -964,20 +964,25 @@ static u64 svm_scale_tsc(struct kvm_vcpu *vcpu, u64 tsc)
         return _tsc;
 }
 
-static void svm_set_tsc_khz(struct kvm_vcpu *vcpu, u32 user_tsc_khz)
+static void svm_set_tsc_khz(struct kvm_vcpu *vcpu, u32 user_tsc_khz, bool scale)
 {
         struct vcpu_svm *svm = to_svm(vcpu);
         u64 ratio;
         u64 khz;
 
-        /* TSC scaling supported? */
-        if (!boot_cpu_has(X86_FEATURE_TSCRATEMSR))
+        /* Guest TSC same frequency as host TSC? */
+        if (!scale) {
+                svm->tsc_ratio = TSC_RATIO_DEFAULT;
                 return;
+        }
 
-        /* TSC-Scaling disabled or guest TSC same frequency as host TSC? */
-        if (user_tsc_khz == 0) {
-                vcpu->arch.virtual_tsc_khz = 0;
-                svm->tsc_ratio = TSC_RATIO_DEFAULT;
+        /* TSC scaling supported? */
+        if (!boot_cpu_has(X86_FEATURE_TSCRATEMSR)) {
+                if (user_tsc_khz > tsc_khz) {
+                        vcpu->arch.tsc_catchup = 1;
+                        vcpu->arch.tsc_always_catchup = 1;
+                } else
+                        WARN(1, "user requested TSC rate below hardware speed\n");
                 return;
         }
 
@@ -992,7 +997,6 @@ static void svm_set_tsc_khz(struct kvm_vcpu *vcpu, u32 user_tsc_khz)
                                 user_tsc_khz);
                 return;
         }
-        vcpu->arch.virtual_tsc_khz = user_tsc_khz;
         svm->tsc_ratio             = ratio;
 }
 
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 3b4c8d8ad906..e6bf61fa1c03 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1817,13 +1817,19 @@ u64 vmx_read_l1_tsc(struct kvm_vcpu *vcpu)
 }
 
 /*
- * Empty call-back. Needs to be implemented when VMX enables the SET_TSC_KHZ
- * ioctl. In this case the call-back should update internal vmx state to make
- * the changes effective.
+ * Engage any workarounds for mis-matched TSC rates.  Currently limited to
+ * software catchup for faster rates on slower CPUs.
  */
-static void vmx_set_tsc_khz(struct kvm_vcpu *vcpu, u32 user_tsc_khz)
+static void vmx_set_tsc_khz(struct kvm_vcpu *vcpu, u32 user_tsc_khz, bool scale)
 {
-        /* Nothing to do here */
+        if (!scale)
+                return;
+
+        if (user_tsc_khz > tsc_khz) {
+                vcpu->arch.tsc_catchup = 1;
+                vcpu->arch.tsc_always_catchup = 1;
+        } else
+                WARN(1, "user requested TSC rate below hardware speed\n");
 }
 
 /*
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2bd77a3a41ed..41bb90acb238 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -96,6 +96,10 @@ EXPORT_SYMBOL_GPL(kvm_has_tsc_control);
 u32  kvm_max_guest_tsc_khz;
 EXPORT_SYMBOL_GPL(kvm_max_guest_tsc_khz);
 
+/* tsc tolerance in parts per million - default to 1/2 of the NTP threshold */
+static u32 tsc_tolerance_ppm = 250;
+module_param(tsc_tolerance_ppm, uint, S_IRUGO | S_IWUSR);
+
 #define KVM_NR_SHARED_MSRS 16
 
 struct kvm_shared_msrs_global {
@@ -968,49 +972,50 @@ static inline u64 get_kernel_ns(void)
 static DEFINE_PER_CPU(unsigned long, cpu_tsc_khz);
 unsigned long max_tsc_khz;
 
-static inline int kvm_tsc_changes_freq(void)
+static inline u64 nsec_to_cycles(struct kvm_vcpu *vcpu, u64 nsec)
 {
-        int cpu = get_cpu();
-        int ret = !boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
-                  cpufreq_quick_get(cpu) != 0;
-        put_cpu();
-        return ret;
+        return pvclock_scale_delta(nsec, vcpu->arch.virtual_tsc_mult,
+                                   vcpu->arch.virtual_tsc_shift);
 }
 
-u64 vcpu_tsc_khz(struct kvm_vcpu *vcpu)
+static u32 adjust_tsc_khz(u32 khz, s32 ppm)
 {
-        if (vcpu->arch.virtual_tsc_khz)
-                return vcpu->arch.virtual_tsc_khz;
-        else
-                return __this_cpu_read(cpu_tsc_khz);
+        u64 v = (u64)khz * (1000000 + ppm);
+        do_div(v, 1000000);
+        return v;
 }
 
-static inline u64 nsec_to_cycles(struct kvm_vcpu *vcpu, u64 nsec)
+static void kvm_set_tsc_khz(struct kvm_vcpu *vcpu, u32 this_tsc_khz)
 {
-        u64 ret;
+        u32 thresh_lo, thresh_hi;
+        int use_scaling = 0;
 
-        WARN_ON(preemptible());
-        if (kvm_tsc_changes_freq())
-                printk_once(KERN_WARNING
-                 "kvm: unreliable cycle conversion on adjustable rate TSC\n");
-        ret = nsec * vcpu_tsc_khz(vcpu);
-        do_div(ret, USEC_PER_SEC);
-        return ret;
-}
-
-static void kvm_init_tsc_catchup(struct kvm_vcpu *vcpu, u32 this_tsc_khz)
-{
         /* Compute a scale to convert nanoseconds in TSC cycles */
         kvm_get_time_scale(this_tsc_khz, NSEC_PER_SEC / 1000,
-                           &vcpu->arch.tsc_catchup_shift,
-                           &vcpu->arch.tsc_catchup_mult);
+                           &vcpu->arch.virtual_tsc_shift,
+                           &vcpu->arch.virtual_tsc_mult);
+        vcpu->arch.virtual_tsc_khz = this_tsc_khz;
+
+        /*
+         * Compute the variation in TSC rate which is acceptable
+         * within the range of tolerance and decide if the
+         * rate being applied is within that bounds of the hardware
+         * rate.  If so, no scaling or compensation need be done.
+         */
+        thresh_lo = adjust_tsc_khz(tsc_khz, -tsc_tolerance_ppm);
+        thresh_hi = adjust_tsc_khz(tsc_khz, tsc_tolerance_ppm);
+        if (this_tsc_khz < thresh_lo || this_tsc_khz > thresh_hi) {
+                pr_debug("kvm: requested TSC rate %u falls outside tolerance [%u,%u]\n", this_tsc_khz, thresh_lo, thresh_hi);
+                use_scaling = 1;
+        }
+        kvm_x86_ops->set_tsc_khz(vcpu, this_tsc_khz, use_scaling);
 }
 
 static u64 compute_guest_tsc(struct kvm_vcpu *vcpu, s64 kernel_ns)
 {
         u64 tsc = pvclock_scale_delta(kernel_ns-vcpu->arch.last_tsc_nsec,
-                                      vcpu->arch.tsc_catchup_mult,
-                                      vcpu->arch.tsc_catchup_shift);
+                                      vcpu->arch.virtual_tsc_mult,
+                                      vcpu->arch.virtual_tsc_shift);
         tsc += vcpu->arch.last_tsc_write;
         return tsc;
 }
@@ -1077,7 +1082,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
         local_irq_save(flags);
         tsc_timestamp = kvm_x86_ops->read_l1_tsc(v);
         kernel_ns = get_kernel_ns();
-        this_tsc_khz = vcpu_tsc_khz(v);
+        this_tsc_khz = __get_cpu_var(cpu_tsc_khz);
         if (unlikely(this_tsc_khz == 0)) {
                 local_irq_restore(flags);
                 kvm_make_request(KVM_REQ_CLOCK_UPDATE, v);
@@ -2804,26 +2809,21 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
                 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);
+                if (user_tsc_khz == 0)
+                        user_tsc_khz = tsc_khz;
+
+                kvm_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);
-
+                r = vcpu->arch.virtual_tsc_khz;
                 goto out;
         }
         default:
@@ -5312,6 +5312,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
                 profile_hit(KVM_PROFILING, (void *)rip);
         }
 
+        if (unlikely(vcpu->arch.tsc_always_catchup))
+                kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
 
         kvm_lapic_sync_from_vapic(vcpu);
 
@@ -6004,7 +6006,7 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
         }
         vcpu->arch.pio_data = page_address(page);
 
-        kvm_init_tsc_catchup(vcpu, max_tsc_khz);
+        kvm_set_tsc_khz(vcpu, max_tsc_khz);
 
         r = kvm_mmu_create(vcpu);
         if (r < 0)