KVM: s390: reverse bit ordering of irqs in pending mask

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 be rejected 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>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

arch/s390/include/asm/kvm_host.h

@@ -422,35 +422,35 @@ 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
 };
 

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,
@@ -1149,8 +1149,8 @@ int __must_check kvm_s390_deliver_pending_interrupts(struct kvm_vcpu *vcpu)
 		set_bit(IRQ_PEND_EXT_CPU_TIMER, &li->pending_irqs);
 
 	while ((irqs = deliverable_irqs(vcpu)) && !rc) {
-		/* bits are in the order of interrupt priority */
-		irq_type = find_first_bit(&irqs, IRQ_PEND_COUNT);
+		/* bits are in the reverse order of interrupt priority */
+		irq_type = find_last_bit(&irqs, IRQ_PEND_COUNT);
 		if (is_ioirq(irq_type)) {
 			rc = __deliver_io(vcpu, irq_type);
 		} else {