linux-kernel - Re: [PATCH] crypto: virtio-crypto: call finalize with bh disabled

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Date:   Wed, 27 Sep 2023 14:12:19 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Halil Pasic <pasic@...ux.ibm.com>
Cc:     "Gonglei (Arei)" <arei.gonglei@...wei.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        Marc Hartmayer <mhartmay@...ux.ibm.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "pizhenwei@...edance.com" <pizhenwei@...edance.com>,
        Halil Pasic <pasic@...ux.ibm.com>
Subject: Re: [PATCH] crypto: virtio-crypto: call finalize with bh disabled

On Wed, Sep 27 2023, Halil Pasic <pasic@...ux.ibm.com> wrote:

> On Wed, 27 Sep 2023 12:08:43 +0200
> Cornelia Huck <cohuck@...hat.com> wrote:
>
>> > On the other hand virtio_airq_handler() calls vring_interrupt() with
>> > interrupts enabled. (While vring_interrupt() is called in a (read)
>> > critical section in virtio_airq_handler() we use read_lock() and
>> > not read_lock_irqsave() to grab the lock. Whether that is correct in
>> > it self (i.e. disregarding the crypto problem) or not I'm not sure right
>> > now. Will think some more about it tomorrow.) If the way to go forward
>> > is disabling interrupts in virtio-ccw before vring_interrupt() is
>> > called, I would be glad to spin a patch for that.  
>> 
>> virtio_airq_handler() is supposed to be an interrupt handler for an
>> adapter interrupt -- as such I would expect it to always run with
>> interrupts disabled (and I'd expect vring_interrupt() to be called
>> with interrupts disabled as well; if that's not the case, I think it
>> would need to run asynchronously.) At least that was my understanding at
>> the time I wrote the code.
>
> Thanks Connie! I don't quite understand what do you mean by "run with
> interrupts disabled" in this context.
>
> Do you mean that if I were to add the following warning:
>
> diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
> index ac67576301bf..2a9c73f5964f 100644
> --- a/drivers/s390/virtio/virtio_ccw.c
> +++ b/drivers/s390/virtio/virtio_ccw.c
> @@ -211,6 +211,8 @@ static void virtio_airq_handler(struct airq_struct *airq,
>         struct airq_info *info = container_of(airq, struct airq_info, airq);
>         unsigned long ai;
>  
> +       WARN_ONCE(in_irq(), "irqs are ought to be disabled but are not\n");
> +
>         inc_irq_stat(IRQIO_VAI);
>
> it would/should never trigger, or do you mean something different?
>
> If yes, does that mean that you would expect the common airq code (i.e. something
> like do_airq_interrupt()) to disable interrupts, or call virtio_airq_handler()?
> asynchronously sort of as a bottom half (my understanding of bottom halves is currently
> not complete).
>
> If no what do you actually mean?

My understanding (at the time) was that we're coming from the low-level
interrupt handler (which disables interrupts via the NEW PSW);
interrupts will be re-enabled once the basic processing is done. This
might no longer be the case, but I currently don't have the time to dig
into the code -- it has been some time.