[KVM timekeeping 30/35] IOCTL for setting TSC rate

[Zachary Amsden]

Add an IOCTL for setting the TSC rate for a VM, intended to
be used to migrate non-kvmclock based VMs which rely on TSC
rate staying stable across host migration.

Signed-off-by: Zachary Amsden <zamsden@xxxxxxxxxx>
---
 arch/x86/kvm/x86.c  |   36 ++++++++++++++++++++++++++++++++++++
 include/linux/kvm.h |    4 ++++
 2 files changed, 40 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 887e30f..e618265 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1017,6 +1017,10 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
 			kvm_x86_ops->adjust_tsc_offset(v, tsc-tsc_timestamp);
 		local_irq_restore(flags);
 
+		/* hw_tsc_khz unknown at creation time, check for overrun */
+		if (this_tsc_khz > v->kvm->arch.virtual_tsc_khz)
+			vcpu->tsc_overrun = 1;
+
 		/* Now, see if we need to switch into trap mode */
 		if (vcpu->tsc_overrun && !vcpu->tsc_trapping)
 			kvm_x86_ops->set_tsc_trap(v, 1);
@@ -1846,6 +1850,7 @@ int kvm_dev_ioctl_check_extension(long ext)
 	case KVM_CAP_DEBUGREGS:
 	case KVM_CAP_X86_ROBUST_SINGLESTEP:
 	case KVM_CAP_XSAVE:
+	case KVM_CAP_SET_TSC_RATE:
 		r = 1;
 		break;
 	case KVM_CAP_COALESCED_MMIO:
@@ -3413,6 +3418,37 @@ long kvm_arch_vm_ioctl(struct file *filp,
 		r = 0;
 		break;
 	}
+	case KVM_X86_GET_TSC_RATE: {
+		u32 rate = kvm->arch.virtual_tsc_khz;
+		r = -EFAULT;
+		if (copy_to_user(argp, &rate, sizeof(rate)))
+			goto out;
+		r = 0;
+		break;
+	}
+	case KVM_X86_SET_TSC_RATE: {
+		u32 rate;
+		int i;
+		struct kvm_vcpu *vcpu;
+		r = -EFAULT;
+		if (copy_from_user(&rate, argp, sizeof rate))
+			goto out;
+		if (rate == 0 || rate > (1ULL << 40)) {
+			r = -EINVAL;
+			break;
+		}
+		/*
+		 * This is intended to be called once, during VM creation.
+		 * Calling this with running VCPUs to dynamically change
+		 * speed is risky; there is no synchronization with the
+		 * compensation loop, so computations using virtual_tsc_khz
+		 * conversions may go haywire.  Use at your own risk.
+		 */
+		kvm_arch_set_tsc_khz(kvm, rate);
+		kvm_for_each_vcpu(i, vcpu, kvm)
+			kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
+		break;
+	}
 
 	default:
 		;
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 3707704..22d27f2 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -539,6 +539,7 @@ struct kvm_ppc_pvinfo {
 #define KVM_CAP_XCRS 56
 #endif
 #define KVM_CAP_PPC_GET_PVINFO 57
+#define KVM_CAP_SET_TSC_RATE 58
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -675,6 +676,9 @@ 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_SET_TSC_RATE */
+#define KVM_X86_GET_TSC_RATE      _IOR(KVMIO,  0xa2, __u32)
+#define KVM_X86_SET_TSC_RATE      _IOW(KVMIO,  0xa3, __u32)
 
 /*
  * ioctls for vcpu fds
-- 
1.7.1

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