From: Paolo Bonzini <pbonzini@redhat.com>
Date: Mon, 7 May 2018 19:24:34 +0200
Patch-mainline: v4.17-rc6
Subject: KVM: hyperv: idr_find needs RCU protection
Git-commit: 452a68d0ef341c4d544757e02154788227b2a08b
References: fate#323887

Even though the eventfd is released after the KVM SRCU grace period
elapses, the conn_to_evt data structure itself is not; it uses RCU
internally, instead.  Fix the read-side critical section to happen
under rcu_read_lock/unlock; the result is still protected by
vcpu->kvm->srcu.

Reviewed-by: Roman Kagan <rkagan@virtuozzo.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Olaf Hering <ohering@suse.de>
---
 arch/x86/kvm/hyperv.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1296,8 +1296,10 @@ static u16 kvm_hvcall_signal_event(struct kvm_vcpu *vcpu, bool fast, u64 param)
 	if (param & ~KVM_HYPERV_CONN_ID_MASK)
 		return HV_STATUS_INVALID_HYPERCALL_INPUT;
 
-	/* conn_to_evt is protected by vcpu->kvm->srcu */
+	/* the eventfd is protected by vcpu->kvm->srcu, but conn_to_evt isn't */
+	rcu_read_lock();
 	eventfd = idr_find(&vcpu->kvm->arch.hyperv.conn_to_evt, param);
+	rcu_read_unlock();
 	if (!eventfd)
 		return HV_STATUS_INVALID_PORT_ID;