[PATCH v6 12/21] KVM: arm64: Separate guest/host counter offset values

[Andrew Jones]

On Wed, Aug 04, 2021 at 08:58:10AM +0000, Oliver Upton wrote:
> In some instances, a VMM may want to update the guest's counter-timer
> offset in a transparent manner, meaning that changes to the hardware
> value do not affect the synthetic register presented to the guest or the
> VMM through said guest's architectural state. Lay the groundwork to
> separate guest offset register writes from the hardware values utilized
> by KVM.
> 
> Signed-off-by: Oliver Upton <oupton at google.com>
> ---
>  arch/arm64/kvm/arch_timer.c  | 48 ++++++++++++++++++++++++++++++++----
>  include/kvm/arm_arch_timer.h |  3 +++
>  2 files changed, 46 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
> index c0101db75ad4..4c2b763a8849 100644
> --- a/arch/arm64/kvm/arch_timer.c
> +++ b/arch/arm64/kvm/arch_timer.c
> @@ -87,6 +87,18 @@ static u64 timer_get_offset(struct arch_timer_context *ctxt)
>  	struct kvm_vcpu *vcpu = ctxt->vcpu;
>  
>  	switch(arch_timer_ctx_index(ctxt)) {
> +	case TIMER_VTIMER:
> +		return ctxt->host_offset;
> +	default:
> +		return 0;
> +	}
> +}
> +
> +static u64 timer_get_guest_offset(struct arch_timer_context *ctxt)
> +{
> +	struct kvm_vcpu *vcpu = ctxt->vcpu;
> +
> +	switch (arch_timer_ctx_index(ctxt)) {
>  	case TIMER_VTIMER:
>  		return __vcpu_sys_reg(vcpu, CNTVOFF_EL2);
>  	default:
> @@ -132,13 +144,31 @@ static void timer_set_offset(struct arch_timer_context *ctxt, u64 offset)
>  
>  	switch(arch_timer_ctx_index(ctxt)) {
>  	case TIMER_VTIMER:
> -		__vcpu_sys_reg(vcpu, CNTVOFF_EL2) = offset;
> +		ctxt->host_offset = offset;
>  		break;
>  	default:
>  		WARN(offset, "timer %ld\n", arch_timer_ctx_index(ctxt));
>  	}
>  }
>  
> +static void timer_set_guest_offset(struct arch_timer_context *ctxt, u64 offset)
> +{
> +	struct kvm_vcpu *vcpu = ctxt->vcpu;
> +
> +	switch (arch_timer_ctx_index(ctxt)) {
> +	case TIMER_VTIMER: {
> +		u64 host_offset = timer_get_offset(ctxt);
> +
> +		host_offset += offset - __vcpu_sys_reg(vcpu, CNTVOFF_EL2);
> +		__vcpu_sys_reg(vcpu, CNTVOFF_EL2) = offset;
> +		timer_set_offset(ctxt, host_offset);
> +		break;
> +	}
> +	default:
> +		WARN_ONCE(offset, "timer %ld\n", arch_timer_ctx_index(ctxt));
> +	}
> +}
> +
>  u64 kvm_phys_timer_read(void)
>  {
>  	return timecounter->cc->read(timecounter->cc);
> @@ -749,7 +779,8 @@ int kvm_timer_vcpu_reset(struct kvm_vcpu *vcpu)
>  
>  /* Make offset updates for all timer contexts atomic */
>  static void update_timer_offset(struct kvm_vcpu *vcpu,
> -				enum kvm_arch_timers timer, u64 offset)
> +				enum kvm_arch_timers timer, u64 offset,
> +				bool guest_visible)
>  {
>  	int i;
>  	struct kvm *kvm = vcpu->kvm;
> @@ -758,13 +789,20 @@ static void update_timer_offset(struct kvm_vcpu *vcpu,
>  	lockdep_assert_held(&kvm->lock);
>  
>  	kvm_for_each_vcpu(i, tmp, kvm)
> -		timer_set_offset(vcpu_get_timer(tmp, timer), offset);
> +		if (guest_visible)
> +			timer_set_guest_offset(vcpu_get_timer(tmp, timer),
> +					       offset);
> +		else
> +			timer_set_offset(vcpu_get_timer(tmp, timer), offset);
>  
>  	/*
>  	 * When called from the vcpu create path, the CPU being created is not
>  	 * included in the loop above, so we just set it here as well.
>  	 */
> -	timer_set_offset(vcpu_get_timer(vcpu, timer), offset);
> +	if (guest_visible)
> +		timer_set_guest_offset(vcpu_get_timer(vcpu, timer), offset);
> +	else
> +		timer_set_offset(vcpu_get_timer(vcpu, timer), offset);
>  }
>  
>  static void update_vtimer_cntvoff(struct kvm_vcpu *vcpu, u64 cntvoff)
> @@ -772,7 +810,7 @@ static void update_vtimer_cntvoff(struct kvm_vcpu *vcpu, u64 cntvoff)
>  	struct kvm *kvm = vcpu->kvm;
>  
>  	mutex_lock(&kvm->lock);
> -	update_timer_offset(vcpu, TIMER_VTIMER, cntvoff);
> +	update_timer_offset(vcpu, TIMER_VTIMER, cntvoff, true);
>  	mutex_unlock(&kvm->lock);
>  }
>  
> diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h
> index 51c19381108c..9d65d4a29f81 100644
> --- a/include/kvm/arm_arch_timer.h
> +++ b/include/kvm/arm_arch_timer.h
> @@ -42,6 +42,9 @@ struct arch_timer_context {
>  	/* Duplicated state from arch_timer.c for convenience */
>  	u32				host_timer_irq;
>  	u32				host_timer_irq_flags;
> +
> +	/* offset relative to the host's physical counter-timer */
> +	u64				host_offset;
>  };
>  
>  struct timer_map {
> -- 
> 2.32.0.605.g8dce9f2422-goog
>

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