[PATCH 1/2] KVM: x86: implement KVM_SET_TSC_PRECISE/KVM_GET_TSC_PRECISE

[Maxim Levitsky <mlevitsk@redhat.com>]

These two new ioctls allow to more precisly capture and
restore guest's TSC state.

Both ioctls are meant to be used to accurately migrate guest TSC
even when there is a significant downtime during the migration.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
 Documentation/virt/kvm/api.rst | 56 +++++++++++++++++++++++++++
 arch/x86/kvm/x86.c             | 69 ++++++++++++++++++++++++++++++++++
 include/uapi/linux/kvm.h       | 14 +++++++
 3 files changed, 139 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 70254eaa5229f..2f04aa8ecf119 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -4826,6 +4826,62 @@ If a vCPU is in running state while this ioctl is invoked, the vCPU may
 experience inconsistent filtering behavior on MSR accesses.
 
 
+4.127 KVM_GET_TSC_STATE
+----------------------------
+
+:Capability: KVM_CAP_PRECISE_TSC
+:Architectures: x86
+:Type: vcpu ioctl
+:Parameters: struct kvm_tsc_info
+:Returns: 0 on success, < 0 on error
+
+::
+
+  #define KVM_TSC_INFO_TSC_ADJUST_VALID 1
+  struct kvm_tsc_info {
+	__u32 flags;
+	__u64 nsec;
+	__u64 tsc;
+	__u64 tsc_adjust;
+  };
+
+flags values for ``struct kvm_tsc_info``:
+
+``KVM_TSC_INFO_TSC_ADJUST_VALID``
+
+  ``tsc_adjust`` contains valid IA32_TSC_ADJUST value
+
+This ioctl allows user space to read guest's IA32_TSC, IA32_TSC_ADJUST,
+and the current value of host CLOCK_REALTIME clock in nanoseconds since unix
+epoch.
+
+
+4.128 KVM_SET_TSC_STATE
+----------------------------
+
+:Capability: KVM_CAP_PRECISE_TSC
+:Architectures: x86
+:Type: vcpu ioctl
+:Parameters: struct kvm_tsc_info
+:Returns: 0 on success, < 0 on error
+
+::
+
+This ioctl allows to reconstruct the guest's IA32_TSC and TSC_ADJUST value
+from the state obtained in the past by KVM_GET_TSC_STATE on the same vCPU.
+
+KVM will adjust the guest TSC value by the time that passed between
+CLOCK_REALTIME timestamp saved in the struct and current value of
+CLOCK_REALTIME, and set guest's TSC to the new value.
+
+TSC_ADJUST is restored as is if KVM_TSC_INFO_TSC_ADJUST_VALID is set.
+
+It is assumed that either both ioctls will be run on the same machine,
+or that source and destination machines have synchronized clocks.
+
+As a special case, it is allowed to leave the timestamp in the struct to zero,
+in which case it will be ignored and the TSC will be restored exactly.
+
 5. The kvm_run structure
 ========================
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a3fdc16cfd6f3..4f0ae9cb14b8a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2438,6 +2438,21 @@ static bool kvm_get_walltime_and_clockread(struct timespec64 *ts,
 
 	return gtod_is_based_on_tsc(do_realtime(ts, tsc_timestamp));
 }
+
+
+static void kvm_get_walltime(u64 *walltime_ns, u64 *host_tsc)
+{
+	struct timespec64 ts;
+
+	if (kvm_get_walltime_and_clockread(&ts, host_tsc)) {
+		*walltime_ns = timespec64_to_ns(&ts);
+		return;
+	}
+
+	*host_tsc = rdtsc();
+	*walltime_ns = ktime_get_real_ns();
+}
+
 #endif
 
 /*
@@ -3757,6 +3772,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_X86_USER_SPACE_MSR:
 	case KVM_CAP_X86_MSR_FILTER:
 	case KVM_CAP_ENFORCE_PV_FEATURE_CPUID:
+#ifdef CONFIG_X86_64
+	case KVM_CAP_PRECISE_TSC:
+#endif
 		r = 1;
 		break;
 	case KVM_CAP_SYNC_REGS:
@@ -4999,6 +5017,57 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 	case KVM_GET_SUPPORTED_HV_CPUID:
 		r = kvm_ioctl_get_supported_hv_cpuid(vcpu, argp);
 		break;
+#ifdef CONFIG_X86_64
+	case KVM_GET_TSC_STATE: {
+		struct kvm_tsc_state __user *user_tsc_state = argp;
+		struct kvm_tsc_state tsc_state;
+		u64 host_tsc;
+
+		memset(&tsc_state, 0, sizeof(tsc_state));
+
+		kvm_get_walltime(&tsc_state.nsec, &host_tsc);
+		tsc_state.tsc = kvm_read_l1_tsc(vcpu, host_tsc);
+
+		if (guest_cpuid_has(vcpu, X86_FEATURE_TSC_ADJUST)) {
+			tsc_state.tsc_adjust = vcpu->arch.ia32_tsc_adjust_msr;
+			tsc_state.flags |= KVM_TSC_STATE_TSC_ADJUST_VALID;
+		}
+
+		r = -EFAULT;
+		if (copy_to_user(user_tsc_state, &tsc_state, sizeof(tsc_state)))
+			goto out;
+		r = 0;
+		break;
+	}
+	case KVM_SET_TSC_STATE: {
+		struct kvm_tsc_state __user *user_tsc_state = argp;
+		struct kvm_tsc_state tsc_state;
+
+		u64 host_tsc, wall_nsec;
+		s64 diff;
+		u64 new_guest_tsc, new_guest_tsc_offset;
+
+		r = -EFAULT;
+		if (copy_from_user(&tsc_state, user_tsc_state, sizeof(tsc_state)))
+			goto out;
+
+		kvm_get_walltime(&wall_nsec, &host_tsc);
+		diff = wall_nsec - tsc_state.nsec;
+
+		if (diff < 0 || tsc_state.nsec == 0)
+			diff = 0;
+
+		new_guest_tsc = tsc_state.tsc + nsec_to_cycles(vcpu, diff);
+		new_guest_tsc_offset = new_guest_tsc - kvm_scale_tsc(vcpu, host_tsc);
+		kvm_vcpu_write_tsc_offset(vcpu, new_guest_tsc_offset);
+
+		if (tsc_state.flags & KVM_TSC_STATE_TSC_ADJUST_VALID)
+			if (guest_cpuid_has(vcpu, X86_FEATURE_TSC_ADJUST))
+				vcpu->arch.ia32_tsc_adjust_msr = tsc_state.tsc_adjust;
+		r = 0;
+		break;
+	}
+#endif
 	default:
 		r = -EINVAL;
 	}
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 886802b8ffba3..ee1bd5e7da964 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1056,6 +1056,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_ENFORCE_PV_FEATURE_CPUID 190
 #define KVM_CAP_SYS_HYPERV_CPUID 191
 #define KVM_CAP_DIRTY_LOG_RING 192
+#define KVM_CAP_PRECISE_TSC 193
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -1169,6 +1170,15 @@ struct kvm_clock_data {
 	__u32 pad[9];
 };
 
+
+#define KVM_TSC_STATE_TSC_ADJUST_VALID 1
+struct kvm_tsc_state {
+	__u32 flags;
+	__u64 nsec;
+	__u64 tsc;
+	__u64 tsc_adjust;
+};
+
 /* For KVM_CAP_SW_TLB */
 
 #define KVM_MMU_FSL_BOOKE_NOHV		0
@@ -1563,6 +1573,10 @@ struct kvm_pv_cmd {
 /* Available with KVM_CAP_DIRTY_LOG_RING */
 #define KVM_RESET_DIRTY_RINGS		_IO(KVMIO, 0xc7)
 
+/* Available with KVM_CAP_PRECISE_TSC*/
+#define KVM_SET_TSC_STATE          _IOW(KVMIO,  0xc8, struct kvm_tsc_state)
+#define KVM_GET_TSC_STATE          _IOR(KVMIO,  0xc9, struct kvm_tsc_state)
+
 /* Secure Encrypted Virtualization command */
 enum sev_cmd_id {
 	/* Guest initialization commands */
-- 
2.26.2