Re: [PATCH v4 09/10] KVM: s390: add and wire function gib_alert_irq_handler()

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On Fri, 30 Nov 2018 15:32:14 +0100
Michael Mueller <mimu@xxxxxxxxxxxxx> wrote:

> The patch implements a handler for GIB alert interruptions
> on the host. Its task is to alert storage backed guests that

What is "storage backed" in this context? Aren't all our guests storage
backed?

> interrupts are pending for them.
> 
> A GIB alert interrupt statistic counter is added as well:
> 
> $ cat /proc/interrupts
>           CPU0       CPU1
>   ...
>   GAL:      23         37   [I/O] GIB Alert
>   ...
> 
> Signed-off-by: Michael Mueller <mimu@xxxxxxxxxxxxx>
> ---
>  arch/s390/include/asm/irq.h |  1 +
>  arch/s390/include/asm/isc.h |  1 +
>  arch/s390/kernel/irq.c      |  1 +
>  arch/s390/kvm/interrupt.c   | 66 ++++++++++++++++++++++++++++++++++++++-------
>  arch/s390/kvm/kvm-s390.h    |  5 ++++
>  5 files changed, 65 insertions(+), 9 deletions(-)
> 


> @@ -2953,6 +2965,9 @@ static void __maybe_unused process_gib_alert_list(void)
>  void kvm_s390_gisa_clear(struct kvm *kvm)
>  {
>  	if (kvm->arch.gisa) {
> +		kvm->arch.gisa->iam = 0;
> +		while (in_alert_list(kvm->arch.gisa))
> +			process_gib_alert_list();

I'm a bit confused. Isn't process_gib_alert_list() to continue
processing until millicode stops adding alerts? Why do you need the
outer while loop, then?

>  		nullify_gisa(kvm->arch.gisa);
>  		VM_EVENT(kvm, 3, "gisa 0x%pK cleared", kvm->arch.gisa);
>  	}
> @@ -2964,9 +2979,9 @@ void kvm_s390_gisa_init(struct kvm *kvm)
>  		kvm->arch.gisa = &kvm->arch.sie_page2->gisa;
>  		kvm->arch.iam = 0;
>  		spin_lock_init(&kvm->arch.iam_ref_lock);
> -		VM_EVENT(kvm, 3, "gisa 0x%pK initialized", kvm->arch.gisa);
> -		kvm_s390_gisa_clear(kvm);
> +		nullify_gisa(kvm->arch.gisa);

Why this change? The only difference here is that the unneeded check
for gisa != NULL is not happening, and the dbf event for clearing is
not logged?

>  		kvm->arch.gib_in_use = !!gib;
> +		VM_EVENT(kvm, 3, "gisa 0x%pK initialized", kvm->arch.gisa);
>  	}
>  }
>  
> @@ -2974,6 +2989,10 @@ void kvm_s390_gisa_destroy(struct kvm *kvm)
>  {
>  	if (!kvm->arch.gisa)
>  		return;
> +
> +	kvm->arch.gisa->iam = 0;
> +	while (in_alert_list(kvm->arch.gisa))
> +		process_gib_alert_list();

Same comment as above. I feel like I'm missing something obvious :(

>  	kvm->arch.gisa = NULL;
>  	kvm->arch.iam = 0;
>  }

>  int kvm_s390_gib_init(u8 nisc)
>  {
> +	int rc = 0;
> +
>  	if (!css_general_characteristics.aiv) {
>  		KVM_EVENT(3, "%s", "gib not initialized, no AIV facility");
> -		return 0;
> +		goto out;

Would be easier to read if you had used the 'goto out' pattern from the
beginning :(

>  	}
>  
>  	gib = (struct kvm_s390_gib *)get_zeroed_page(GFP_KERNEL | GFP_DMA);
>  	if (!gib) {
>  		KVM_EVENT(3, "gib 0x%pK memory allocation failed", gib);
> -		return -ENOMEM;
> +		rc = -ENOMEM;
> +		goto out;
> +	}
> +
> +	gib_alert_irq.isc = nisc;
> +	if (register_adapter_interrupt(&gib_alert_irq)) {
> +		KVM_EVENT(3, "gib 0x%pK GAI registration failed", gib);

I think this should be logged to the syslog as well, so you can find
out what went wrong for modular kvm.

> +		rc = -EIO;
> +		goto out_free;
>  	}
>  
>  	gib->nisc = nisc;
>  	if (chsc_sgib((u32)(u64)gib)) {
>  		KVM_EVENT(3, "gib 0x%pK AIV association failed", gib);
> -		free_page((unsigned long)gib);
> -		gib = NULL;
> -		return -EIO;
> +		rc = -EIO;
> +		goto out_unreg;
>  	}
>  
>  	KVM_EVENT(3, "gib 0x%pK (nisc=%d) initialized", gib, gib->nisc);
> -	return 0;
> +	return rc;
> +
> +out_unreg:
> +	unregister_adapter_interrupt(&gib_alert_irq);
> +out_free:
> +	free_page((unsigned long)gib);
> +	gib = NULL;
> +out:
> +	return rc;
>  }



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