Re: [PATCH RFC 1/6] KVM: s390: take care of clock-comparator sign control

["Collin L. Walling" <walling@linux.vnet.ibm.com>]

On 02/07/2018 06:46 AM, David Hildenbrand wrote:
> Missed when enabling the Multiple-epoch facility. If the facility is
> installed and the control is set, a sign based comaprison has to be
> performed.
>
> Right now we would inject wrong interrupts and ignore interrupt
> conditions. Also the sleep time is calculated in a wrong way.
>
> Signed-off-by: David Hildenbrand<david@redhat.com>
> ---
>   arch/s390/kvm/interrupt.c | 25 +++++++++++++++++++------
>   1 file changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
> index 3ea9cfa31b16..a616e9b65f91 100644
> --- a/arch/s390/kvm/interrupt.c
> +++ b/arch/s390/kvm/interrupt.c
> @@ -169,8 +169,15 @@ static int ckc_interrupts_enabled(struct kvm_vcpu *vcpu)
>
>   static int ckc_irq_pending(struct kvm_vcpu *vcpu)
>   {
> -	if (vcpu->arch.sie_block->ckc >= kvm_s390_get_tod_clock_fast(vcpu->kvm))
> +	const u64 now = kvm_s390_get_tod_clock_fast(vcpu->kvm);
> +	const u64 ckc = vcpu->arch.sie_block->ckc;
> +
> +	if (vcpu->arch.sie_block->gcr[0] & 0x0020000000000000ul) {
> +		if ((s64)ckc >= (s64)now)
> +			return 0;
> +	} else if (ckc >= now) {
>   		return 0;
> +	}
>   	return ckc_interrupts_enabled(vcpu);
>   }
>
> @@ -1042,13 +1049,19 @@ int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu)
>
>   static u64 __calculate_sltime(struct kvm_vcpu *vcpu)
>   {
> -	u64 now, cputm, sltime = 0;
> +	const u64 now = kvm_s390_get_tod_clock_fast(vcpu->kvm);
> +	const u64 ckc = vcpu->arch.sie_block->ckc;
> +	u64 cputm, sltime = 0;
>
>   	if (ckc_interrupts_enabled(vcpu)) {
> -		now = kvm_s390_get_tod_clock_fast(vcpu->kvm);
> -		sltime = tod_to_ns(vcpu->arch.sie_block->ckc - now);
> -		/* already expired or overflow? */
> -		if (!sltime || vcpu->arch.sie_block->ckc <= now)
> +		if (vcpu->arch.sie_block->gcr[0] & 0x0020000000000000ul) {
> +			if ((s64)now < (s64)ckc)
> +				sltime = tod_to_ns((s64)ckc - (s64)now);
> +		} else if (now < ckc) {
> +			sltime = tod_to_ns(ckc - now);
> +		}
> +		/* already expired */
> +		if (!sltime)
>   			return 0;
>   		if (cpu_timer_interrupts_enabled(vcpu)) {
>   			cputm = kvm_s390_get_cpu_timer(vcpu);
I think it would assist with readability if you defined the sign 
comparison bit. Seeing
something that yells "SIGNED" would make sense as to what's going on here.

Other than that, I don't see anything wrong.

I'll get to reviewing the rest of these patches throughout the day. I 
have to revisit
the docs :)

-- 
- Collin L Walling