KVM: s390: Remove unneeded srcu lock

JIRA: https://issues.redhat.com/browse/RHEL-113452

commit 7e42ad6
Author: Claudio Imbrenda <imbrenda@linux.ibm.com>
Date:   Wed May 28 11:55:00 2025 +0200

    KVM: s390: Remove unneeded srcu lock

    All paths leading to handle_essa() already hold the kvm->srcu.
    Remove unneeded srcu locking from handle_essa().
    Add lockdep assertion to make sure we will always be holding kvm->srcu
    when entering handle_essa().

    Reviewed-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
    Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
    Reviewed-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
    Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
    Link: https://lore.kernel.org/r/20250528095502.226213-3-imbrenda@linux.ibm.com
    Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
    Message-ID: <20250528095502.226213-3-imbrenda@linux.ibm.com>

Signed-off-by: Thomas Huth <thuth@redhat.com>

Author: huth

arch/s390/kvm/priv.c

@@ -1248,6 +1248,8 @@ static inline int __do_essa(struct kvm_vcpu *vcpu, const int orc)
 
 static int handle_essa(struct kvm_vcpu *vcpu)
 {
+	lockdep_assert_held(&vcpu->kvm->srcu);
+
 	/* entries expected to be 1FF */
 	int entries = (vcpu->arch.sie_block->cbrlo & ~PAGE_MASK) >> 3;
 	unsigned long *cbrlo;
@@ -1297,12 +1299,8 @@ 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;