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

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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>

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This commit is contained in:

Michael Mueller 2017-06-29 18:39:27 +02:00 • committed by Christian Borntraeger

parent 8d5fb0dc4e

commit c7901a6ebe

2 changed files with 33 additions and 33 deletions

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54

arch/s390/include/asm/kvm_host.h

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12

arch/s390/kvm/interrupt.c

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