[PATCH v3 08/12] KVM: arm64: Allow userspace to configure a vCPU's virtual offset

[Andrew Jones]

On Mon, Jul 19, 2021 at 06:49:45PM +0000, Oliver Upton wrote:
> 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.
> 
> 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;
>  	}
>  
> -- 
> 2.32.0.402.g57bb445576-goog
> 
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>

 
Reviewed-by: Andrew Jones <drjones at redhat.com>