Re: [PATCH 01/12] KVM: s390: reverse bit ordering of irqs in pending mask

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On 16.01.2018 21:02, Christian Borntraeger wrote:
> From: Michael Mueller <mimu@xxxxxxxxxxxxxxxxxx>
> 
> This patch prepares a simplification of bit operations between the irq
> pending mask for emulated interrupts and the Interruption Pending Mask
> (IPM) which is part of the Guest Interruption State Area (GISA), a feature
> that allows interrupt delivery to guests by means of the SIE instruction.
> 
> Without that change, a bit-wise *or* operation on parts of these two masks
> would either require a look-up table of size 256 bytes to map the IPM
> to the emulated irq pending mask bit orientation (all bits mirrored at half
> byte) or a sequence of up to 8 condidional branches to perform tests of
> single bit positions. Both options are to reject either by performance or
> space utilization reasons.
> 
> Beyond that this change will be transparent.
> 
> Signed-off-by: Michael Mueller <mimu@xxxxxxxxxxxxxxxxxx>
> Reviewed-by: Halil Pasic <pasic@xxxxxxxxxxxxxxxxxx>
> Reviewed-by: Pierre Morel <pmorel@xxxxxxxxxxxxxxxxxx>
> Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> ---
>  arch/s390/include/asm/kvm_host.h | 54 ++++++++++++++++++++--------------------
>  arch/s390/kvm/interrupt.c        | 10 ++++----
>  2 files changed, 32 insertions(+), 32 deletions(-)
> 
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index e16a9f2a44ad..9981721f258f 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -409,35 +409,35 @@ struct kvm_vcpu_stat {
>  #define PGM_PER				0x80
>  #define PGM_CRYPTO_OPERATION		0x119
>  
> -/* irq types in order of priority */
> +/* irq types in ascend order of priorities */
>  enum irq_types {
> -	IRQ_PEND_MCHK_EX = 0,
> -	IRQ_PEND_SVC,
> -	IRQ_PEND_PROG,
> -	IRQ_PEND_MCHK_REP,
> -	IRQ_PEND_EXT_IRQ_KEY,
> -	IRQ_PEND_EXT_MALFUNC,
> -	IRQ_PEND_EXT_EMERGENCY,
> -	IRQ_PEND_EXT_EXTERNAL,
> -	IRQ_PEND_EXT_CLOCK_COMP,
> -	IRQ_PEND_EXT_CPU_TIMER,
> -	IRQ_PEND_EXT_TIMING,
> -	IRQ_PEND_EXT_SERVICE,
> -	IRQ_PEND_EXT_HOST,
> -	IRQ_PEND_PFAULT_INIT,
> -	IRQ_PEND_PFAULT_DONE,
> -	IRQ_PEND_VIRTIO,
> -	IRQ_PEND_IO_ISC_0,
> -	IRQ_PEND_IO_ISC_1,
> -	IRQ_PEND_IO_ISC_2,
> -	IRQ_PEND_IO_ISC_3,
> -	IRQ_PEND_IO_ISC_4,
> -	IRQ_PEND_IO_ISC_5,
> -	IRQ_PEND_IO_ISC_6,
> -	IRQ_PEND_IO_ISC_7,
> -	IRQ_PEND_SIGP_STOP,
> +	IRQ_PEND_SET_PREFIX = 0,
>  	IRQ_PEND_RESTART,
> -	IRQ_PEND_SET_PREFIX,
> +	IRQ_PEND_SIGP_STOP,
> +	IRQ_PEND_IO_ISC_7,
> +	IRQ_PEND_IO_ISC_6,
> +	IRQ_PEND_IO_ISC_5,
> +	IRQ_PEND_IO_ISC_4,
> +	IRQ_PEND_IO_ISC_3,
> +	IRQ_PEND_IO_ISC_2,
> +	IRQ_PEND_IO_ISC_1,
> +	IRQ_PEND_IO_ISC_0,
> +	IRQ_PEND_VIRTIO,
> +	IRQ_PEND_PFAULT_DONE,
> +	IRQ_PEND_PFAULT_INIT,
> +	IRQ_PEND_EXT_HOST,
> +	IRQ_PEND_EXT_SERVICE,
> +	IRQ_PEND_EXT_TIMING,
> +	IRQ_PEND_EXT_CPU_TIMER,
> +	IRQ_PEND_EXT_CLOCK_COMP,
> +	IRQ_PEND_EXT_EXTERNAL,
> +	IRQ_PEND_EXT_EMERGENCY,
> +	IRQ_PEND_EXT_MALFUNC,
> +	IRQ_PEND_EXT_IRQ_KEY,
> +	IRQ_PEND_MCHK_REP,
> +	IRQ_PEND_PROG,
> +	IRQ_PEND_SVC,
> +	IRQ_PEND_MCHK_EX,
>  	IRQ_PEND_COUNT

We have to touch all because of irq priority, right?

>  };
>  
> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
> index f8eb2cfa763a..b94173560dcf 100644
> --- a/arch/s390/kvm/interrupt.c
> +++ b/arch/s390/kvm/interrupt.c
> @@ -189,8 +189,8 @@ static int cpu_timer_irq_pending(struct kvm_vcpu *vcpu)
>  
>  static inline int is_ioirq(unsigned long irq_type)
>  {
> -	return ((irq_type >= IRQ_PEND_IO_ISC_0) &&
> -		(irq_type <= IRQ_PEND_IO_ISC_7));
> +	return ((irq_type >= IRQ_PEND_IO_ISC_7) &&
> +		(irq_type <= IRQ_PEND_IO_ISC_0));
>  }
>  
>  static uint64_t isc_to_isc_bits(int isc)
> @@ -211,12 +211,12 @@ static inline unsigned long pending_irqs(struct kvm_vcpu *vcpu)
>  
>  static inline int isc_to_irq_type(unsigned long isc)
>  {
> -	return IRQ_PEND_IO_ISC_0 + isc;
> +	return IRQ_PEND_IO_ISC_0 - isc;
>  }
>  
>  static inline int irq_type_to_isc(unsigned long irq_type)
>  {
> -	return irq_type - IRQ_PEND_IO_ISC_0;
> +	return IRQ_PEND_IO_ISC_0 - irq_type;
>  }
>  
>  static unsigned long disable_iscs(struct kvm_vcpu *vcpu,
> @@ -1155,7 +1155,7 @@ int __must_check kvm_s390_deliver_pending_interrupts(struct kvm_vcpu *vcpu)
>  
>  	while ((irqs = deliverable_irqs(vcpu)) && !rc) {
>  		/* bits are in the order of interrupt priority */

this comment should now be "reversed order"

> -		irq_type = find_first_bit(&irqs, IRQ_PEND_COUNT);
> +		irq_type = find_last_bit(&irqs, IRQ_PEND_COUNT);
>  		if (is_ioirq(irq_type)) {
>  			rc = __deliver_io(vcpu, irq_type);
>  		} else {
> 

Looks sane to me on the first sight.

-- 

Thanks,

David / dhildenb
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