linux-kernel - [RFC] KVM: s390: pci: register pci hooks without interpretation

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Message-Id: <20220920192739.135174-1-mjrosato@linux.ibm.com>
Date:   Tue, 20 Sep 2022 15:27:39 -0400
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     linux-s390@...r.kernel.org
Cc:     farman@...ux.ibm.com, schnelle@...ux.ibm.com, pmorel@...ux.ibm.com,
        borntraeger@...ux.ibm.com, frankja@...ux.ibm.com,
        imbrenda@...ux.ibm.com, david@...hat.com, hca@...ux.ibm.com,
        gor@...ux.ibm.com, agordeev@...ux.ibm.com, svens@...ux.ibm.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC] KVM: s390: pci: register pci hooks without interpretation

The kvm registration hooks must be registered even if the facilities
necessary for zPCI interpretation are unavailable, as vfio-pci-zdev will
expect to use the hooks regardless.
This fixes an issue where vfio-pci-zdev will fail its open function
because of a missing kvm_register when running on hardware that does not
support zPCI interpretation.

Fixes: ca922fecda6c ("KVM: s390: pci: Hook to access KVM lowlevel from VFIO")
Signed-off-by: Matthew Rosato <mjrosato@...ux.ibm.com>
---
 arch/s390/kvm/kvm-s390.c |  4 ++--
 arch/s390/kvm/pci.c      | 14 +++++++++++---
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index e20e126944aa..5c7f5f97ea09 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -510,7 +510,7 @@ int kvm_arch_init(void *opaque)
 		goto out;
 	}
 
-	if (kvm_s390_pci_interp_allowed()) {
+	if (IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM)) {
 		rc = kvm_s390_pci_init();
 		if (rc) {
 			pr_err("Unable to allocate AIFT for PCI\n");
@@ -532,7 +532,7 @@ int kvm_arch_init(void *opaque)
 void kvm_arch_exit(void)
 {
 	kvm_s390_gib_destroy();
-	if (kvm_s390_pci_interp_allowed())
+	if (IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM))
 		kvm_s390_pci_exit();
 	debug_unregister(kvm_s390_dbf);
 	debug_unregister(kvm_s390_dbf_uv);
diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
index 3c12637ce08c..81457dfeae91 100644
--- a/arch/s390/kvm/pci.c
+++ b/arch/s390/kvm/pci.c
@@ -672,23 +672,31 @@ int kvm_s390_pci_zpci_op(struct kvm *kvm, struct kvm_s390_zpci_op *args)
 
 int kvm_s390_pci_init(void)
 {
+	zpci_kvm_hook.kvm_register = kvm_s390_pci_register_kvm;
+	zpci_kvm_hook.kvm_unregister = kvm_s390_pci_unregister_kvm;
+
+	if (!kvm_s390_pci_interp_allowed())
+		return 0;
+
 	aift = kzalloc(sizeof(struct zpci_aift), GFP_KERNEL);
 	if (!aift)
 		return -ENOMEM;
 
 	spin_lock_init(&aift->gait_lock);
 	mutex_init(&aift->aift_lock);
-	zpci_kvm_hook.kvm_register = kvm_s390_pci_register_kvm;
-	zpci_kvm_hook.kvm_unregister = kvm_s390_pci_unregister_kvm;
 
 	return 0;
 }
 
 void kvm_s390_pci_exit(void)
 {
-	mutex_destroy(&aift->aift_lock);
 	zpci_kvm_hook.kvm_register = NULL;
 	zpci_kvm_hook.kvm_unregister = NULL;
 
+	if (!kvm_s390_pci_interp_allowed())
+		return;
+
+	mutex_destroy(&aift->aift_lock);
+
 	kfree(aift);
 }
-- 
2.37.3