Re: [PATCH v5 13/15] KVM: s390: add function process_gib_alert_list()

[Pierre Morel]

On 09/01/2019 14:10, Halil Pasic wrote:
> On Wed, 9 Jan 2019 13:14:17 +0100
> Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:
>
> > On 08/01/2019 16:21, Michael Mueller wrote:
> > > On 08.01.19 13:59, Halil Pasic wrote:
> > > > On Wed, 19 Dec 2018 20:17:54 +0100
> > > > Michael Mueller <mimu@xxxxxxxxxxxxx> wrote:
> > > >
> > > > > This function processes the Gib Alert List (GAL). It is required
> > > > > to run when either a gib alert interruption has been received or
> > > > > a gisa that is in the alert list is cleared or dropped.
> > > > >
> > > > > The GAL is build up by millicode, when the respective ISC bit is
> > > > > set in the Interruption Alert Mask (IAM) and an interruption of
> > > > > that class is observed.
> > > > >
> > > > > Signed-off-by: Michael Mueller <mimu@xxxxxxxxxxxxx>
> > > > > ---
> > > > >  Â arch/s390/kvm/interrupt.c | 140
> > > > > ++++++++++++++++++++++++++++++++++++++++++++++
> > > > >  Â 1 file changed, 140 insertions(+)
> > > > >
> > > > > diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
> > > > > index 48a93f5e5333..03e7ba4f215a 100644
> > > > > --- a/arch/s390/kvm/interrupt.c
> > > > > +++ b/arch/s390/kvm/interrupt.c
> > > > > @@ -2941,6 +2941,146 @@ int kvm_s390_get_irq_state(struct kvm_vcpu
> > > > > *vcpu, __u8 __user *buf, int len)
> > > > >  ÂÂÂÂÂ return n;
> > > > >  Â }
> > > > > +static int __try_airqs_kick(struct kvm *kvm, u8 ipm)
> > > > > +{
> > > > > +ÂÂÂ struct kvm_s390_float_interrupt *fi = &kvm->arch.float_int;
> > > > > +ÂÂÂ struct kvm_vcpu *vcpu = NULL, *kick_vcpu[MAX_ISC + 1];
> > > > > +ÂÂÂ int online_vcpus = atomic_read(&kvm->online_vcpus);
> > > > > +ÂÂÂ u8 ioint_mask, isc_mask, kick_mask = 0x00;
> > > > > +ÂÂÂ int vcpu_id, kicked = 0;
> > > > > +
> > > > > +ÂÂÂ /* Loop over vcpus in WAIT state. */
> > > > > +ÂÂÂ for (vcpu_id = find_first_bit(fi->idle_mask, online_vcpus);
> > > > > +ÂÂÂÂÂÂÂÂ /* Until all pending ISCs have a vcpu open for airqs. */
> > > > > +ÂÂÂÂÂÂÂÂ (~kick_mask & ipm) && vcpu_id < online_vcpus;
> > > > > +ÂÂÂÂÂÂÂÂ vcpu_id = find_next_bit(fi->idle_mask, online_vcpus,
> > > > > vcpu_id)) {
> > > > > +ÂÂÂÂÂÂÂ vcpu = kvm_get_vcpu(kvm, vcpu_id);
> > > > > +ÂÂÂÂÂÂÂ if (psw_ioint_disabled(vcpu))
> > > > > +ÂÂÂÂÂÂÂÂÂÂÂ continue;
> > > > > +ÂÂÂÂÂÂÂ ioint_mask = (u8)(vcpu->arch.sie_block->gcr[6] >> 24);
> > > > > +ÂÂÂÂÂÂÂ for (isc_mask = 0x80; isc_mask; isc_mask >>= 1) {
> > > > > +ÂÂÂÂÂÂÂÂÂÂÂ /* ISC pending in IPM ? */
> > > > > +ÂÂÂÂÂÂÂÂÂÂÂ if (!(ipm & isc_mask))
> > > > > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ continue;
> > > > > +ÂÂÂÂÂÂÂÂÂÂÂ /* vcpu for this ISC already found ? */
> > > > > +ÂÂÂÂÂÂÂÂÂÂÂ if (kick_mask & isc_mask)
> > > > > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ continue;
> > > > > +ÂÂÂÂÂÂÂÂÂÂÂ /* vcpu open for airq of this ISC ? */
> > > > > +ÂÂÂÂÂÂÂÂÂÂÂ if (!(ioint_mask & isc_mask))
> > > > > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ continue;
> > > > > +ÂÂÂÂÂÂÂÂÂÂÂ /* use this vcpu (for all ISCs in ioint_mask) */
> > > > > +ÂÂÂÂÂÂÂÂÂÂÂ kick_mask |= ioint_mask;
> > > > > +ÂÂÂÂÂÂÂÂÂÂÂ kick_vcpu[kicked++] = vcpu;
> > > >
> > > > Assuming that the vcpu can/will take all ISCs it's currently open for
> > > > does not seem right. We kind of rely on this assumption here, or?
> >
> > why does it not seem right?
>
> When an interrupt is delivered a psw-swap takes place. The new-psw
> may fence IO interrupts. Thus for example if we have the vcpu open for
> all ISCs and 0, 1 and 2 pending, we may end up only delivering 0, if the
> psw-swap corresponding to delivering 0 closes the vcpu for IO
> interrupts. After guest has control, we don't have control over the rest
> of the story.

OK I think I understand your concern, waking up a single waiting vCPU 
per ISC is not enough.
We must wake all vCPU in wait state having at least one matching ISC bit.

Regards,
Pierre


--
Pierre Morel
Linux/KVM/QEMU in BÃblingen - Germany