[PATCH v4 09/13] KVM: arm64: Allow userspace to configure a vCPU's virtual offset

[Oliver Upton]

Add a new vCPU attribute that allows userspace to directly manipulate
the virtual counter-timer offset. Exposing such an interface allows for
the precise migration of guest virtual counter-timers, as it is an
indepotent interface.

Uphold the existing behavior of writes to CNTVOFF_EL2 for this new
interface, wherein a write to a single vCPU is broadcasted to all vCPUs
within a VM.

Reviewed-by: Andrew Jones <drjones at redhat.com>
Signed-off-by: Oliver Upton <oupton at google.com>
---
 Documentation/virt/kvm/devices/vcpu.rst | 22 ++++++++
 arch/arm64/include/uapi/asm/kvm.h       |  1 +
 arch/arm64/kvm/arch_timer.c             | 68 ++++++++++++++++++++++++-
 3 files changed, 89 insertions(+), 2 deletions(-)

diff --git a/Documentation/virt/kvm/devices/vcpu.rst b/Documentation/virt/kvm/devices/vcpu.rst
index b46d5f742e69..7b57cba3416a 100644
--- a/Documentation/virt/kvm/devices/vcpu.rst
+++ b/Documentation/virt/kvm/devices/vcpu.rst
@@ -139,6 +139,28 @@ configured values on other VCPUs.  Userspace should configure the interrupt
 numbers on at least one VCPU after creating all VCPUs and before running any
 VCPUs.
 
+2.2. ATTRIBUTE: KVM_ARM_VCPU_TIMER_OFFSET_VTIMER
+------------------------------------------------
+
+:Parameters: Pointer to a 64-bit unsigned counter-timer offset.
+
+Returns:
+
+	 ======= ======================================
+	 -EFAULT Error reading/writing the provided
+	 	 parameter address
+	 -ENXIO  Attribute not supported
+	 ======= ======================================
+
+Specifies the guest's virtual counter-timer offset from the host's
+virtual counter. The guest's virtual counter is then derived by
+the following equation:
+
+  guest_cntvct = host_cntvct - KVM_ARM_VCPU_TIMER_OFFSET_VTIMER
+
+KVM does not allow the use of varying offset values for different vCPUs;
+the last written offset value will be broadcasted to all vCPUs in a VM.
+
 3. GROUP: KVM_ARM_VCPU_PVTIME_CTRL
 ==================================
 
diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index b3edde68bc3e..008d0518d2b1 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -365,6 +365,7 @@ struct kvm_arm_copy_mte_tags {
 #define KVM_ARM_VCPU_TIMER_CTRL		1
 #define   KVM_ARM_VCPU_TIMER_IRQ_VTIMER		0
 #define   KVM_ARM_VCPU_TIMER_IRQ_PTIMER		1
+#define   KVM_ARM_VCPU_TIMER_OFFSET_VTIMER	2
 #define KVM_ARM_VCPU_PVTIME_CTRL	2
 #define   KVM_ARM_VCPU_PVTIME_IPA	0
 
diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
index 3df67c127489..d2b1b13af658 100644
--- a/arch/arm64/kvm/arch_timer.c
+++ b/arch/arm64/kvm/arch_timer.c
@@ -1305,7 +1305,7 @@ static void set_timer_irqs(struct kvm *kvm, int vtimer_irq, int ptimer_irq)
 	}
 }
 
-int kvm_arm_timer_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
+int kvm_arm_timer_set_attr_irq(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 {
 	int __user *uaddr = (int __user *)(long)attr->addr;
 	struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
@@ -1338,7 +1338,39 @@ int kvm_arm_timer_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 	return 0;
 }
 
-int kvm_arm_timer_get_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
+int kvm_arm_timer_set_attr_offset(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
+{
+	u64 __user *uaddr = (u64 __user *)(long)attr->addr;
+	u64 offset;
+
+	if (get_user(offset, uaddr))
+		return -EFAULT;
+
+	switch (attr->attr) {
+	case KVM_ARM_VCPU_TIMER_OFFSET_VTIMER:
+		update_vtimer_cntvoff(vcpu, offset);
+		break;
+	default:
+		return -ENXIO;
+	}
+
+	return 0;
+}
+
+int kvm_arm_timer_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
+{
+	switch (attr->attr) {
+	case KVM_ARM_VCPU_TIMER_IRQ_VTIMER:
+	case KVM_ARM_VCPU_TIMER_IRQ_PTIMER:
+		return kvm_arm_timer_set_attr_irq(vcpu, attr);
+	case KVM_ARM_VCPU_TIMER_OFFSET_VTIMER:
+		return kvm_arm_timer_set_attr_offset(vcpu, attr);
+	}
+
+	return -ENXIO;
+}
+
+int kvm_arm_timer_get_attr_irq(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 {
 	int __user *uaddr = (int __user *)(long)attr->addr;
 	struct arch_timer_context *timer;
@@ -1359,11 +1391,43 @@ int kvm_arm_timer_get_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 	return put_user(irq, uaddr);
 }
 
+int kvm_arm_timer_get_attr_offset(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
+{
+	u64 __user *uaddr = (u64 __user *)(long)attr->addr;
+	struct arch_timer_context *timer;
+	u64 offset;
+
+	switch (attr->attr) {
+	case KVM_ARM_VCPU_TIMER_OFFSET_VTIMER:
+		timer = vcpu_vtimer(vcpu);
+		break;
+	default:
+		return -ENXIO;
+	}
+
+	offset = timer_get_offset(timer);
+	return put_user(offset, uaddr);
+}
+
+int kvm_arm_timer_get_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
+{
+	switch (attr->attr) {
+	case KVM_ARM_VCPU_TIMER_IRQ_VTIMER:
+	case KVM_ARM_VCPU_TIMER_IRQ_PTIMER:
+		return kvm_arm_timer_get_attr_irq(vcpu, attr);
+	case KVM_ARM_VCPU_TIMER_OFFSET_VTIMER:
+		return kvm_arm_timer_get_attr_offset(vcpu, attr);
+	}
+
+	return -ENXIO;
+}
+
 int kvm_arm_timer_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 {
 	switch (attr->attr) {
 	case KVM_ARM_VCPU_TIMER_IRQ_VTIMER:
 	case KVM_ARM_VCPU_TIMER_IRQ_PTIMER:
+	case KVM_ARM_VCPU_TIMER_OFFSET_VTIMER:
 		return 0;
 	}
 
-- 
2.32.0.432.gabb21c7263-goog