linux-kernel - [PATCH 1/3] KVM: x86: Accept KVM_[GS]ET_TSC

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Date:   Fri, 25 Feb 2022 14:53:02 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org,
        Suleiman Souhlal <suleiman@...gle.com>,
        Anton Romanov <romanton@...gle.com>
Subject: [PATCH 1/3] KVM: x86: Accept KVM_[GS]ET_TSC_KHZ as a VM ioctl.

From: David Woodhouse <dwmw@...zon.co.uk>

This sets the default TSC frequency for subsequently created vCPUs.

Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
---
 Documentation/virt/kvm/api.rst  | 11 +++++++----
 arch/x86/include/asm/kvm_host.h |  2 ++
 arch/x86/kvm/x86.c              | 26 +++++++++++++++++++++++++-
 include/uapi/linux/kvm.h        |  4 +++-
 4 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 046b386f6ce3..982fcdf8cfa8 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -1903,22 +1903,25 @@ 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
 
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index a3385db39d3e..e4696a578f41 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1119,6 +1119,8 @@ 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;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 83accd3e7502..bb3e9916229a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4308,6 +4308,7 @@ 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:
@@ -6483,6 +6484,28 @@ 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)
@@ -11165,7 +11188,7 @@ 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);
@@ -11614,6 +11637,7 @@ 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;
 
 #if IS_ENABLED(CONFIG_HYPERV)
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 22a1aa98fa9e..01ae8b0e90f8 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1134,6 +1134,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_VM_GPA_BITS 207
 #define KVM_CAP_XSAVE2 208
 #define KVM_CAP_SYS_ATTRIBUTES 209
+#define KVM_CAP_VM_TSC_CONTROL 210
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -1461,7 +1462,8 @@ 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 */
-- 
2.33.1