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

David Hildenbrand
2018-01-16T20:18:58Z

On 16.01.2018 21:02, Christian Borntraeger wrote:
> From: Michael Mueller <mimu@linux.vnet.ibm.com>
>
> 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@linux.vnet.ibm.com>
> Reviewed-by: Halil Pasic <pasic@linux.vnet.ibm.com>
> Reviewed-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> ---
> 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