KVM: x86: Accept KVM_[GS]ET_TSC_KHZ as a VM ioctl.

This sets the default TSC frequency for subsequently created vCPUs.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20220225145304.36166-2-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Documentation/virt/kvm/api.rst

@@ -1897,22 +1897,25 @@ the future.
 4.55 KVM_SET_TSC_KHZ
 --------------------
 
-:Capability: KVM_CAP_TSC_CONTROL
+:Capability: KVM_CAP_TSC_CONTROL / KVM_CAP_VM_TSC_CONTROL
 :Architectures: x86
-:Type: vcpu ioctl
+:Type: vcpu ioctl / vm 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.
 
+If the KVM_CAP_VM_TSC_CONTROL capability is advertised, this can also
+be used as a vm ioctl to set the initial tsc frequency of subsequently
+created vCPUs.
 
 4.56 KVM_GET_TSC_KHZ
 --------------------
 
-:Capability: KVM_CAP_GET_TSC_KHZ
+:Capability: KVM_CAP_GET_TSC_KHZ / KVM_CAP_VM_TSC_CONTROL
 :Architectures: x86
-:Type: vcpu ioctl
+:Type: vcpu ioctl / vm ioctl
 :Parameters: none
 :Returns: virtual tsc-khz on success, negative value on error
 

arch/x86/include/asm/kvm_host.h

@@ -1126,6 +1126,8 @@ struct kvm_arch {
 	u64 cur_tsc_generation;
 	int nr_vcpus_matched_tsc;
 
+	u32 default_tsc_khz;
+
 	seqcount_raw_spinlock_t pvclock_sc;
 	bool use_master_clock;
 	u64 master_kernel_ns;

arch/x86/kvm/x86.c

@@ -4324,6 +4324,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 		r = boot_cpu_has(X86_FEATURE_XSAVE);
 		break;
 	case KVM_CAP_TSC_CONTROL:
+	case KVM_CAP_VM_TSC_CONTROL:
 		r = kvm_has_tsc_control;
 		break;
 	case KVM_CAP_X2APIC_API:
@@ -6522,6 +6523,28 @@ long kvm_arch_vm_ioctl(struct file *filp,
 	case KVM_GET_CLOCK:
 		r = kvm_vm_ioctl_get_clock(kvm, argp);
 		break;
+	case KVM_SET_TSC_KHZ: {
+		u32 user_tsc_khz;
+
+		r = -EINVAL;
+		user_tsc_khz = (u32)arg;
+
+		if (kvm_has_tsc_control &&
+		    user_tsc_khz >= kvm_max_guest_tsc_khz)
+			goto out;
+
+		if (user_tsc_khz == 0)
+			user_tsc_khz = tsc_khz;
+
+		WRITE_ONCE(kvm->arch.default_tsc_khz, user_tsc_khz);
+		r = 0;
+
+		goto out;
+	}
+	case KVM_GET_TSC_KHZ: {
+		r = READ_ONCE(kvm->arch.default_tsc_khz);
+		goto out;
+	}
 	case KVM_MEMORY_ENCRYPT_OP: {
 		r = -ENOTTY;
 		if (!kvm_x86_ops.mem_enc_ioctl)
@@ -11266,7 +11289,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
 	kvm_xen_init_vcpu(vcpu);
 	kvm_vcpu_mtrr_init(vcpu);
 	vcpu_load(vcpu);
-	kvm_set_tsc_khz(vcpu, max_tsc_khz);
+	kvm_set_tsc_khz(vcpu, vcpu->kvm->arch.default_tsc_khz);
 	kvm_vcpu_reset(vcpu, false);
 	kvm_init_mmu(vcpu);
 	vcpu_put(vcpu);
@@ -11714,6 +11737,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	pvclock_update_vm_gtod_copy(kvm);
 	raw_spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags);
 
+	kvm->arch.default_tsc_khz = max_tsc_khz;
 	kvm->arch.guest_can_read_msr_platform_info = true;
 	kvm->arch.enable_pmu = enable_pmu;
 

include/uapi/linux/kvm.h

@@ -1144,6 +1144,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_S390_MEM_OP_EXTENSION 211
 #define KVM_CAP_PMU_CAPABILITY 212
 #define KVM_CAP_DISABLE_QUIRKS2 213
+#define KVM_CAP_VM_TSC_CONTROL 214
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -1471,7 +1472,8 @@ struct kvm_s390_ucas_mapping {
 #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 */
+/* Available with KVM_CAP_TSC_CONTROL for a vCPU, or with
+*  KVM_CAP_VM_TSC_CONTROL to set defaults for a VM */
 #define KVM_SET_TSC_KHZ           _IO(KVMIO,  0xa2)
 #define KVM_GET_TSC_KHZ           _IO(KVMIO,  0xa3)
 /* Available with KVM_CAP_PCI_2_3 */