Re: [PATCH v4 1/4] s390/crypto: Replace cond_resched() with msleep(1)

[Holger Dengler <dengler@linux.ibm.com>]

On 7/31/26 18:50, Heiko Carstens wrote:
> From: Peter Zijlstra <peterz@infradead.org>
> 
> With [1] cond_resched() is always compiled away and becomes a no-op.
> 
> The comments for all cond_resched() calls in crypto code however indicate
> that the current process should be scheduled away to avoid instant
> re-invocation of a callback. This is not what cond_resched() would do or
> did.
> 
> Instead of just removing the cond_resched() calls, replace them with
> msleep() calls, as suggested by Holger Dengler. This forces the current
> task to be scheduled away (sleeps) like originally intended.
> 
> Holger provided information why this intended [2]:
> "
> Let me give a bit of background here: The protected key can only get
> invalid, if the Linux instance (z/VM or KVM guest) is moved to another
> hypervisor on a different machine (aka life guest relocation). In such a
> case, the crypto accelerator card and the host has to exchange the "real
> key", which is wrapped by the host and handed back to the guest as the
> re-newed protected key. Unfortunately there is no asynchronous trigger
> on completion, you have to re-try (and maybe get another "in progress"
> return).
> 
> And as if that weren't bad enough, if this key exchange between card and
> host is the first one, card and host has to instantiate a secure
> communication channel (including a key exchange for the transport layer).
> "
> 
> [1] commit 7dadeaa6e851 ("sched: Further restrict the preemption modes")
> [2] https://lore.kernel.org/all/39570813-27b0-40f9-89c5-8e2dce05e2f0@linux.ibm.com/
> [3] https://lore.kernel.org/all/20260731084027.GE776954@noisy.programming.kicks-ass.net/
> 
> [hca@linux.ibm.com: took Peter's patch [3] and provided commit message]
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

Reviewed-by: Holger Dengler <dengler@linux.ibm.com>

-- 
Mit freundlichen Grüßen / Kind regards
Holger Dengler