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SubjectRe: [PATCH v6 11/13] KVM: s390: add functions to (un)register GISC with GISA
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?

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;
> +}

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