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>

5 files changed, 90 insertions, 0 deletions

diff --git a/Documentation/kvm/api.txt b/Documentation/kvm/api.txt
index 9bef4e4cec50..1b9eaa7e8856 100644
--- a/Documentation/kvm/api.txt
+++ b/Documentation/kvm/api.txt
@@ -1263,6 +1263,29 @@ struct kvm_assigned_msix_entry {
         __u16 padding[3];
 };
 
+4.54 KVM_SET_TSC_KHZ
+
+Capability: KVM_CAP_TSC_CONTROL
+Architectures: x86
+Type: vcpu ioctl
+Parameters: virtual tsc_khz
+Returns: 0 on success, -1 on error
+
+Specifies the tsc frequency for the virtual machine. The unit of the
+frequency is KHz.
+
+4.55 KVM_GET_TSC_KHZ
+
+Capability: KVM_CAP_GET_TSC_KHZ
+Architectures: x86
+Type: vcpu ioctl
+Parameters: none
+Returns: virtual tsc-khz on success, negative value on error
+
+Returns the tsc frequency of the guest. The unit of the return value is
+KHz. If the host has unstable tsc this ioctl returns -EIO instead as an
+error.
+
 5. The kvm_run structure
 
 Application code obtains a pointer to the kvm_run structure by
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index da0a8ce3a139..bd57639fd5db 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -655,6 +655,13 @@ u8 kvm_get_guest_memory_type(struct kvm_vcpu *vcpu, gfn_t gfn);
 
 extern bool tdp_enabled;
 
+/* control of guest tsc rate supported? */
+extern bool kvm_has_tsc_control;
+/* minimum supported tsc_khz for guests */
+extern u32  kvm_min_guest_tsc_khz;
+/* maximum supported tsc_khz for guests */
+extern u32  kvm_max_guest_tsc_khz;
+
 enum emulation_result {
         EMULATE_DONE,       /* no further processing */
         EMULATE_DO_MMIO,      /* kvm_run filled with mmio request */
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 8c4549bef4ed..a98873762433 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 579ce34e7904..1d5a7f418795 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;
         }
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index ea2dc1a2e13d..2f63ebeac639 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -541,6 +541,8 @@ struct kvm_ppc_pvinfo {
 #define KVM_CAP_PPC_GET_PVINFO 57
 #define KVM_CAP_PPC_IRQ_LEVEL 58
 #define KVM_CAP_ASYNC_PF 59
+#define KVM_CAP_TSC_CONTROL 60
+#define KVM_CAP_GET_TSC_KHZ 61
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -677,6 +679,9 @@ struct kvm_clock_data {
 #define KVM_SET_PIT2              _IOW(KVMIO,  0xa0, struct kvm_pit_state2)
 /* Available with KVM_CAP_PPC_GET_PVINFO */
 #define KVM_PPC_GET_PVINFO        _IOW(KVMIO,  0xa1, struct kvm_ppc_pvinfo)
+/* Available with KVM_CAP_TSC_CONTROL */
+#define KVM_SET_TSC_KHZ           _IO(KVMIO,  0xa2)
+#define KVM_GET_TSC_KHZ           _IO(KVMIO,  0xa3)
 
 /*
  * ioctls for vcpu fds