On Thu, 16 Apr 2020 08:17:21 +0200
Christian Borntraeger <borntraeger@xxxxxxxxxx> wrote:
> On 15.04.20 21:03, Eric Farman wrote:
> > The diag 0x44 handler, which handles a directed yield, goes into a
> > a codepath that does a kvm_for_each_vcpu() and ultimately
> > deliverable_irqs(). The new check for kvm_s390_pv_cpu_is_protected()
> > contains an assertion that the vcpu->mutex is held, which isn't going
> > to be the case in this scenario.
> >
> > The result is a plethora of these messages if the lock debugging
> > is enabled, and thus an implication that we have a problem.
> >
> > WARNING: CPU: 9 PID: 16167 at arch/s390/kvm/kvm-s390.h:239 deliverable_irqs+0x1c6/0x1d0 [kvm]
> > ...snip...
> > Call Trace:
> > [<000003ff80429bf2>] deliverable_irqs+0x1ca/0x1d0 [kvm]
> > ([<000003ff80429b34>] deliverable_irqs+0x10c/0x1d0 [kvm])
> > [<000003ff8042ba82>] kvm_s390_vcpu_has_irq+0x2a/0xa8 [kvm]
> > [<000003ff804101e2>] kvm_arch_dy_runnable+0x22/0x38 [kvm]
> > [<000003ff80410284>] kvm_vcpu_on_spin+0x8c/0x1d0 [kvm]
> > [<000003ff80436888>] kvm_s390_handle_diag+0x3b0/0x768 [kvm]
> > [<000003ff80425af4>] kvm_handle_sie_intercept+0x1cc/0xcd0 [kvm]
> > [<000003ff80422bb0>] __vcpu_run+0x7b8/0xfd0 [kvm]
> > [<000003ff80423de6>] kvm_arch_vcpu_ioctl_run+0xee/0x3e0 [kvm]
> > [<000003ff8040ccd8>] kvm_vcpu_ioctl+0x2c8/0x8d0 [kvm]
> > [<00000001504ced06>] ksys_ioctl+0xae/0xe8
> > [<00000001504cedaa>] __s390x_sys_ioctl+0x2a/0x38
> > [<0000000150cb9034>] system_call+0xd8/0x2d8
> > 2 locks held by CPU 2/KVM/16167:
> > #0: 00000001951980c0 (&vcpu->mutex){+.+.}, at: kvm_vcpu_ioctl+0x90/0x8d0 [kvm]
> > #1: 000000019599c0f0 (&kvm->srcu){....}, at: __vcpu_run+0x4bc/0xfd0 [kvm]
> > Last Breaking-Event-Address:
> > [<000003ff80429b34>] deliverable_irqs+0x10c/0x1d0 [kvm]
> > irq event stamp: 11967
> > hardirqs last enabled at (11975): [<00000001502992f2>] console_unlock+0x4ca/0x650
> > hardirqs last disabled at (11982): [<0000000150298ee8>] console_unlock+0xc0/0x650
> > softirqs last enabled at (7940): [<0000000150cba6ca>] __do_softirq+0x422/0x4d8
> > softirqs last disabled at (7929): [<00000001501cd688>] do_softirq_own_stack+0x70/0x80
> >
> > Considering what's being done here, let's fix this by removing the
> > mutex assertion rather than acquiring the mutex for every other vcpu.
> >
> > Fixes: 201ae986ead7 ("KVM: s390: protvirt: Implement interrupt injection")
>
> Yes, when adding that check I missed that path. We do have other places that use
> kvm_s390_pv_cpu_get_handle instead of kvm_s390_pv_cpu_is_protected when we know
> that this place has cases without the mutex being hold. And yes kvm_vcpu_on_spin
> is such a place.
>
> The alternative would be to copy kvm_s390_vcpu_has_irq into a newly create
> s390 version of kvm_arch_dy_runnable with a private copy of kvm_s390_vcpu_has_irq.
> I think your patch is preferrable as it avoids code duplication with just tiny
> difference. After all it is just a sanity check.
I agree, calling kvm_s390_pv_cpu_get_handle() in that code path without
the mutex is fine, and I don't think we would benefit a lot from
keeping the check in the general case and using a special case for the
directed yield check.
>
> Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Reviewed-by: Cornelia Huck <cohuck@xxxxxxxxxx>
>
> > Signed-off-by: Eric Farman <farman@xxxxxxxxxxxxx>
> > ---
> > arch/s390/kvm/interrupt.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
> > index 8191106bf7b9..bfb481134994 100644
> > --- a/arch/s390/kvm/interrupt.c
> > +++ b/arch/s390/kvm/interrupt.c
> > @@ -393,7 +393,7 @@ static unsigned long deliverable_irqs(struct kvm_vcpu *vcpu)
> > if (psw_mchk_disabled(vcpu))
> > active_mask &= ~IRQ_PEND_MCHK_MASK;
> > /* PV guest cpus can have a single interruption injected at a time. */
> > - if (kvm_s390_pv_cpu_is_protected(vcpu) &&
> > + if (kvm_s390_pv_cpu_get_handle(vcpu) &&
> > vcpu->arch.sie_block->iictl != IICTL_CODE_NONE)
> > active_mask &= ~(IRQ_PEND_EXT_II_MASK |
> > IRQ_PEND_IO_MASK |
> >
>
