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.
Reviewed-by: Christian Borntraeger <borntraeger@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 |
>
