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SubjectRe: [PATCH v6 11/13] KVM: s390: add functions to (un)register GISC with GISA
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On 29.01.19 14:09, Cornelia Huck wrote:
> On Thu, 24 Jan 2019 13:59:37 +0100
> Michael Mueller <mimu@linux.ibm.com> wrote:
>
>> Add the Interruption Alert Mask (IAM) to the architecture specific
>> kvm struct. This mask in the GISA is used to define for which ISC
>> a GIB alert will be issued.
>>
>> The functions kvm_s390_gisc_register() and kvm_s390_gisc_unregister()
>> are used to (un)register a GISC (guest ISC) with a virtual machine and
>> its GISA.
>>
>> Upon successful completion, kvm_s390_gisc_register() returns the
>> ISC to be used for GIB alert interruptions. A negative return code
>> indicates an error during registration.
>>
>> Theses functions will be used by other adapter types like AP and PCI to
>> request pass-through interruption support.
>>
>> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
>> ---
>> arch/s390/include/asm/kvm_host.h | 13 +++++
>> arch/s390/kvm/interrupt.c | 117 +++++++++++++++++++++++++++++++++++++++
>> 2 files changed, 130 insertions(+)
>>
>
>> +int kvm_s390_gisc_register(struct kvm *kvm, u32 gisc)
>> +{
>> + struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
>> + u8 alert_mask;
>> +
>> + if (!gi->origin)
>> + return -ENODEV;
>> + if (gisc > MAX_ISC)
>> + return -ERANGE;
>> +
>> + spin_lock(&gi->alert.ref_lock);
>> + if (gi->alert.ref_count[gisc] == 0) {
>
> If the ref_count is 0 here...
>
>> + alert_mask = gi->alert.mask | 0x80 >> gisc;
>> + WRITE_ONCE(gi->alert.mask, alert_mask);
>> + }
>> + gi->alert.ref_count[gisc]++;
>> + if (gi->alert.ref_count[gisc] == 1)
>
> ...it will certainly be 1 here, won't it?

Sure, the increment is unconditional and can be done right away.
Thus it is logically the same and now symmetric to the unregister
function:

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index ba314da746b7..f37dfb01c63c 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -2976,11 +2976,11 @@ int kvm_s390_gisc_register(struct kvm *kvm, u32
gisc)
return -ERANGE;

spin_lock(&gi->alert.ref_lock);
- if (gi->alert.ref_count[gisc] == 0)
- gi->alert.mask |= 0x80 >> gisc;
gi->alert.ref_count[gisc]++;
- if (gi->alert.ref_count[gisc] == 1)
+ if (gi->alert.ref_count[gisc] == 1) {
+ gi->alert.mask |= 0x80 >> gisc;
gisa_set_iam(gi->origin, gi->alert.mask);
+ }
spin_unlock(&gi->alert.ref_lock);

return gib->nisc;

>
> Can you do all of the manipulations in a single if branch?
>
>> + gisa_set_iam(gi->origin, alert_mask);
>> + spin_unlock(&gi->alert.ref_lock);
>> +
>> + return gib->nisc;
>> +}
>

Thanks,
Michael

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