Virtualization - Sep 2023 - [PATCH] crypto: virtio-crypto: call finalize with bh disabled

On Tue, Sep 26 2023, Halil Pasic <pasic at linux.ibm.com> wrote:
> [..]
>> --- a/drivers/crypto/virtio/virtio_crypto_akcipher_algs.c
>> +++ b/drivers/crypto/virtio/virtio_crypto_akcipher_algs.c
>> @@ -61,8 +61,9 @@ static void virtio_crypto_akcipher_finalize_req(
>>  	vc_akcipher_req->src_buf = NULL;
>>  	vc_akcipher_req->dst_buf = NULL;
>>  	virtcrypto_clear_request(&vc_akcipher_req->base);
>> -
>> +	local_bh_disable();
>>  
crypto_finalize_akcipher_request(vc_akcipher_req->base.dataq->engine, req,
err);
>> +	local_bh_enable();
>
> Thanks Gonglei!
>
> I did this a quick spin, and it does not seem to be sufficient on s390x.
> Which does not come as a surprise to me, because 
>
> #define lockdep_assert_in_softirq()                                     \
> do {                                                                    \
>         WARN_ON_ONCE(__lockdep_enabled                  &&         
\
>                      (!in_softirq() || in_irq() || in_nmi()));          \
> } while (0)
>
> will still warn because  in_irq() still evaluates to true (your patch
> addresses the !in_softirq() part).
>
> I don't have any results on x86 yet. My current understanding is that
the
> virtio-pci transport code disables interrupts locally somewhere in the
> call chain (actually in vp_vring_interrupt() via spin_lock_irqsave())
> and then x86 would be fine. But I will get that verified.
>
> 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.
>
> Copying Conny, as she may have an opinion on this (if I'm not wrong she
> authored that code).
>
> Regards,
> Halil

On Wed, 27 Sep 2023 12:08:43 +0200
Cornelia Huck <cohuck at redhat.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?

Regards,
Halil

Regards,
Halil