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

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Date:   Wed, 27 Sep 2023 12:08:43 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Halil Pasic <pasic@...ux.ibm.com>,
        "Gonglei (Arei)" <arei.gonglei@...wei.com>
Cc:     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 Tue, Sep 26 2023, Halil Pasic <pasic@...ux.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