From 51fd783c09c2268ad82eea223e87e3e64e843180 Mon Sep 17 00:00:00 2001
From: David Woodhouse <dwmw@amazon.co.uk>
Date: Mon, 26 Dec 2022 11:24:40 +0000
Subject: [PATCH] Revert "KVM: x86/xen: Fix SRCU/RCU usage in readers of
 evtchn_ports"

This reverts commit 0ae356e28968715e0d7fb8608e3f6e1caf5e2dad.
---
 arch/x86/kvm/xen.c | 36 +++++++++++-------------------------
 1 file changed, 11 insertions(+), 25 deletions(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 935f845d005ca..d7af402402484 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -1825,23 +1825,20 @@ static int kvm_xen_eventfd_update(struct kvm *kvm,
 {
 	u32 port = data->u.evtchn.send_port;
 	struct evtchnfd *evtchnfd;
-	int ret;
 
 	if (!port || port >= max_evtchn_port(kvm))
 		return -EINVAL;
 
-	/* Protect writes to evtchnfd as well as the idr lookup.  */
 	mutex_lock(&kvm->lock);
 	evtchnfd = idr_find(&kvm->arch.xen.evtchn_ports, port);
+	mutex_unlock(&kvm->lock);
 
-	ret = -ENOENT;
 	if (!evtchnfd)
-		goto out_unlock;
+		return -ENOENT;
 
 	/* For an UPDATE, nothing may change except the priority/vcpu */
-	ret = -EINVAL;
 	if (evtchnfd->type != data->u.evtchn.type)
-		goto out_unlock;
+		return -EINVAL;
 
 	/*
 	 * Port cannot change, and if it's zero that was an eventfd
@@ -1849,21 +1846,20 @@ static int kvm_xen_eventfd_update(struct kvm *kvm,
 	 */
 	if (!evtchnfd->deliver.port.port ||
 	    evtchnfd->deliver.port.port != data->u.evtchn.deliver.port.port)
-		goto out_unlock;
+		return -EINVAL;
 
 	/* We only support 2 level event channels for now */
 	if (data->u.evtchn.deliver.port.priority != KVM_IRQ_ROUTING_XEN_EVTCHN_PRIO_2LEVEL)
-		goto out_unlock;
+		return -EINVAL;
 
+	mutex_lock(&kvm->lock);
 	evtchnfd->deliver.port.priority = data->u.evtchn.deliver.port.priority;
 	if (evtchnfd->deliver.port.vcpu_id != data->u.evtchn.deliver.port.vcpu) {
 		evtchnfd->deliver.port.vcpu_id = data->u.evtchn.deliver.port.vcpu;
 		evtchnfd->deliver.port.vcpu_idx = -1;
 	}
-	ret = 0;
-out_unlock:
 	mutex_unlock(&kvm->lock);
-	return ret;
+	return 0;
 }
 
 /*
@@ -2009,23 +2005,19 @@ static bool kvm_xen_hcall_evtchn_send(struct kvm_vcpu *vcpu, u64 param, u64 *r)
 	gpa_t gpa;
 	int idx;
 
-	/*
-	 * evtchnfd is protected by kvm->srcu; the idr lookup instead
-	 * is protected by RCU.
-	 */
 	idx = srcu_read_lock(&vcpu->kvm->srcu);
 	gpa = kvm_mmu_gva_to_gpa_system(vcpu, param, NULL);
+	srcu_read_unlock(&vcpu->kvm->srcu, idx);
 
 	if (!gpa || kvm_vcpu_read_guest(vcpu, gpa, &send, sizeof(send))) {
 		*r = -EFAULT;
-		goto out_handled;
+		return true;
 	}
 
-	rcu_read_lock();
+	/* The evtchn_ports idr is protected by vcpu->kvm->srcu */
 	evtchnfd = idr_find(&vcpu->kvm->arch.xen.evtchn_ports, send.port);
-	rcu_read_unlock();
 	if (!evtchnfd)
-		goto out_not_handled;
+		return false;
 
 	if (evtchnfd->deliver.port.port) {
 		int ret = kvm_xen_set_evtchn(&evtchnfd->deliver.port, vcpu->kvm);
@@ -2036,13 +2028,7 @@ static bool kvm_xen_hcall_evtchn_send(struct kvm_vcpu *vcpu, u64 param, u64 *r)
 	}
 
 	*r = 0;
-out_handled:
-	srcu_read_unlock(&vcpu->kvm->srcu, idx);
 	return true;
-
-out_not_handled:
-	srcu_read_unlock(&vcpu->kvm->srcu, idx);
-	return false;
 }
 
 void kvm_xen_init_vcpu(struct kvm_vcpu *vcpu)
-- 
2.50.1