Re: [PATCH v1 2/5] KVM: s390: remove unneeded srcu lock

[Nina Schoetterl-Glausch]

On Wed, 2025-05-14 at 18:38 +0200, Claudio Imbrenda wrote:
> All paths leading to handle_essa() already hold the kvm->srcu.
> Remove unneeded srcu locking from handle_essa().
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>

Reviewed-by: Nina Schoetterl-Glausch <nsg@xxxxxxxxxxxxx>

Why are you removing it tho?
It should be very low cost and it makes the code more robust,
since handle_essa itself ensures that it has the lock.
It is also easier to understand which synchronization the function does.
You could of course add a comment stating that the kvm srcu read side needs
to be held. I think this would be good to have if you really don't want the
srcu_read_lock here.
But then you might also want that documented up the call chain.

> ---
>  arch/s390/kvm/priv.c | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
> index 1a49b89706f8..758cefb5bac7 100644
> --- a/arch/s390/kvm/priv.c
> +++ b/arch/s390/kvm/priv.c
> @@ -1297,12 +1297,8 @@ static int handle_essa(struct kvm_vcpu *vcpu)
>  		/* Retry the ESSA instruction */
>  		kvm_s390_retry_instr(vcpu);
>  	} else {
> -		int srcu_idx;
> -
>  		mmap_read_lock(vcpu->kvm->mm);
> -		srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
>  		i = __do_essa(vcpu, orc);
> -		srcu_read_unlock(&vcpu->kvm->srcu, srcu_idx);
>  		mmap_read_unlock(vcpu->kvm->mm);
>  		if (i < 0)
>  			return i;

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