linux-kernel - [PATCH 2/2] KVM: s390: pci: use asyncronous kvm put

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Message-Id: <20230109201037.33051-3-mjrosato@linux.ibm.com>
Date:   Mon,  9 Jan 2023 15:10:37 -0500
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     alex.williamson@...hat.com, pbonzini@...hat.com
Cc:     jgg@...dia.com, cohuck@...hat.com, farman@...ux.ibm.com,
        pmorel@...ux.ibm.com, borntraeger@...ux.ibm.com,
        frankja@...ux.ibm.com, imbrenda@...ux.ibm.com, david@...hat.com,
        akrowiak@...ux.ibm.com, jjherne@...ux.ibm.com, pasic@...ux.ibm.com,
        zhenyuw@...ux.intel.com, zhi.a.wang@...el.com,
        linux-s390@...r.kernel.org, kvm@...r.kernel.org,
        intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] KVM: s390: pci: use asyncronous kvm put

It's possible that the kvm refcount will reach 0 at this point while the
associated device is still in kvm device list - this would result in a
deadlock on the vfio group lock.  Avoid this possibility by using
kvm_put_kvm_async to do the kvm_destroy_vm asynchronously.

Fixes: 09340b2fca00 ("KVM: s390: pci: add routines to start/stop interpretive execution")
Signed-off-by: Matthew Rosato <mjrosato@...ux.ibm.com>
---
 arch/s390/kvm/pci.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
index ec51e810e381..d1d528438138 100644
--- a/arch/s390/kvm/pci.c
+++ b/arch/s390/kvm/pci.c
@@ -509,7 +509,7 @@ static int kvm_s390_pci_register_kvm(void *opaque, struct kvm *kvm)
 		kvm_s390_pci_dev_release(zdev);
 	mutex_unlock(&kvm->lock);
 	mutex_unlock(&zdev->kzdev_lock);
-	kvm_put_kvm(kvm);
+	kvm_put_kvm_async(kvm);
 	return rc;
 }
 
@@ -567,7 +567,11 @@ static void kvm_s390_pci_unregister_kvm(void *opaque)
 	mutex_unlock(&kvm->lock);
 	mutex_unlock(&zdev->kzdev_lock);
 
-	kvm_put_kvm(kvm);
+	/*
+	 * Avoid possible deadlock on any currently-held vfio lock by
+	 * ensuring the potential kvm_destroy_vm call is done asynchronously
+	 */
+	kvm_put_kvm_async(kvm);
 }
 
 void kvm_s390_pci_init_list(struct kvm *kvm)
-- 
2.39.0