MIPS: KVM: Add count frequency KVM register

Expose the KVM guest CP0_Count frequency to userland via a new
KVM_REG_MIPS_COUNT_HZ register accessible with the KVM_{GET,SET}_ONE_REG
ioctls.

When the frequency is altered the bias is adjusted such that the guest
CP0_Count doesn't jump discontinuously or lose any timer interrupts.
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: kvm@vger.kernel.org
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: David Daney <david.daney@cavium.com>
Cc: Sanjay Lal <sanjayl@kymasys.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/mips/include/asm/kvm_host.h

@@ -720,6 +720,7 @@ void kvm_mips_write_compare(struct kvm_vcpu *vcpu, uint32_t compare);
 void kvm_mips_init_count(struct kvm_vcpu *vcpu);
 int kvm_mips_set_count_ctl(struct kvm_vcpu *vcpu, s64 count_ctl);
 int kvm_mips_set_count_resume(struct kvm_vcpu *vcpu, s64 count_resume);
+int kvm_mips_set_count_hz(struct kvm_vcpu *vcpu, s64 count_hz);
 void kvm_mips_count_enable_cause(struct kvm_vcpu *vcpu);
 void kvm_mips_count_disable_cause(struct kvm_vcpu *vcpu);
 enum hrtimer_restart kvm_mips_count_timeout(struct kvm_vcpu *vcpu);

arch/mips/include/uapi/asm/kvm.h

@@ -133,6 +133,13 @@ struct kvm_fpu {
  */
 #define KVM_REG_MIPS_COUNT_RESUME	(KVM_REG_MIPS | KVM_REG_SIZE_U64 | \
 					 0x20000 | 1)
+/*
+ * CP0_Count rate in Hz
+ * Specifies the rate of the CP0_Count timer in Hz. Modifications occur without
+ * discontinuities in CP0_Count.
+ */
+#define KVM_REG_MIPS_COUNT_HZ		(KVM_REG_MIPS | KVM_REG_SIZE_U64 | \
+					 0x20000 | 2)
 
 /*
  * KVM MIPS specific structures and definitions

arch/mips/kvm/kvm_mips.c

@@ -546,6 +546,7 @@ static u64 kvm_mips_get_one_regs[] = {
 
 	KVM_REG_MIPS_COUNT_CTL,
 	KVM_REG_MIPS_COUNT_RESUME,
+	KVM_REG_MIPS_COUNT_HZ,
 };
 
 static int kvm_mips_get_reg(struct kvm_vcpu *vcpu,
@@ -627,6 +628,7 @@ static int kvm_mips_get_reg(struct kvm_vcpu *vcpu,
 	case KVM_REG_MIPS_CP0_COUNT:
 	case KVM_REG_MIPS_COUNT_CTL:
 	case KVM_REG_MIPS_COUNT_RESUME:
+	case KVM_REG_MIPS_COUNT_HZ:
 		ret = kvm_mips_callbacks->get_one_reg(vcpu, reg, &v);
 		if (ret)
 			return ret;
@@ -724,6 +726,7 @@ static int kvm_mips_set_reg(struct kvm_vcpu *vcpu,
 	case KVM_REG_MIPS_CP0_CAUSE:
 	case KVM_REG_MIPS_COUNT_CTL:
 	case KVM_REG_MIPS_COUNT_RESUME:
+	case KVM_REG_MIPS_COUNT_HZ:
 		return kvm_mips_callbacks->set_one_reg(vcpu, reg, v);
 	default:
 		return -EINVAL;

arch/mips/kvm/kvm_mips_emul.c

@@ -497,6 +497,54 @@ void kvm_mips_init_count(struct kvm_vcpu *vcpu)
 	kvm_mips_write_count(vcpu, 0);
 }
 
+/**
+ * kvm_mips_set_count_hz() - Update the frequency of the timer.
+ * @vcpu:	Virtual CPU.
+ * @count_hz:	Frequency of CP0_Count timer in Hz.
+ *
+ * Change the frequency of the CP0_Count timer. This is done atomically so that
+ * CP0_Count is continuous and no timer interrupt is lost.
+ *
+ * Returns:	-EINVAL if @count_hz is out of range.
+ *		0 on success.
+ */
+int kvm_mips_set_count_hz(struct kvm_vcpu *vcpu, s64 count_hz)
+{
+	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	int dc;
+	ktime_t now;
+	u32 count;
+
+	/* ensure the frequency is in a sensible range... */
+	if (count_hz <= 0 || count_hz > NSEC_PER_SEC)
+		return -EINVAL;
+	/* ... and has actually changed */
+	if (vcpu->arch.count_hz == count_hz)
+		return 0;
+
+	/* Safely freeze timer so we can keep it continuous */
+	dc = kvm_mips_count_disabled(vcpu);
+	if (dc) {
+		now = kvm_mips_count_time(vcpu);
+		count = kvm_read_c0_guest_count(cop0);
+	} else {
+		now = kvm_mips_freeze_hrtimer(vcpu, &count);
+	}
+
+	/* Update the frequency */
+	vcpu->arch.count_hz = count_hz;
+	vcpu->arch.count_period = div_u64((u64)NSEC_PER_SEC << 32, count_hz);
+	vcpu->arch.count_dyn_bias = 0;
+
+	/* Calculate adjusted bias so dynamic count is unchanged */
+	vcpu->arch.count_bias = count - kvm_mips_ktime_to_count(vcpu, now);
+
+	/* Update and resume hrtimer */
+	if (!dc)
+		kvm_mips_resume_hrtimer(vcpu, now, count);
+	return 0;
+}
+
 /**
  * kvm_mips_write_compare() - Modify compare and update timer.
  * @vcpu:	Virtual CPU.

arch/mips/kvm/kvm_trap_emul.c

@@ -415,6 +415,9 @@ static int kvm_trap_emul_get_one_reg(struct kvm_vcpu *vcpu,
 	case KVM_REG_MIPS_COUNT_RESUME:
 		*v = ktime_to_ns(vcpu->arch.count_resume);
 		break;
+	case KVM_REG_MIPS_COUNT_HZ:
+		*v = vcpu->arch.count_hz;
+		break;
 	default:
 		return -EINVAL;
 	}
@@ -461,6 +464,9 @@ static int kvm_trap_emul_set_one_reg(struct kvm_vcpu *vcpu,
 	case KVM_REG_MIPS_COUNT_RESUME:
 		ret = kvm_mips_set_count_resume(vcpu, v);
 		break;
+	case KVM_REG_MIPS_COUNT_HZ:
+		ret = kvm_mips_set_count_hz(vcpu, v);
+		break;
 	default:
 		return -EINVAL;
 	}