From: Tony Krowiak <akrowiak@linux.ibm.com>
Date: Mon, 23 Aug 2021 17:20:47 -0400
Subject: s390/vfio-ap: replace open coded locks for VFIO_GROUP_NOTIFY_SET_KVM
notification
Git-commit: 86956e70761b3292156d668e87126844334dd71b
Patch-mainline: v5.15-rc1
References: bsc#1205701
It was pointed out during an unrelated patch review that locks should not
be open coded - i.e., writing the algorithm of a standard lock in a
function instead of using a lock from the standard library. The setting and
testing of a busy flag and sleeping on a wait_event is the same thing
a lock does. The open coded locks are invisible to lockdep, so potential
locking problems are not detected.
This patch removes the open coded locks used during
VFIO_GROUP_NOTIFY_SET_KVM notification. The busy flag
and wait queue were introduced to resolve a possible circular locking
dependency reported by lockdep when starting a secure execution guest
configured with AP adapters and domains. Reversing the order in which
the kvm->lock mutex and matrix_dev->lock mutex are locked resolves the
issue reported by lockdep, thus enabling the removal of the open coded
locks.
Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
Acked-by: Halil Pasic <pasic@linux.ibm.com>
Link: https://lore.kernel.org/r/20210823212047.1476436-3-akrowiak@linux.ibm.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Acked-by: Joerg Roedel <jroedel@suse.de>
---
arch/s390/kvm/kvm-s390.c | 31 ++++++-
drivers/s390/crypto/vfio_ap_ops.c | 132 ++++++++++------------------------
drivers/s390/crypto/vfio_ap_private.h | 2
3 files changed, 67 insertions(+), 98 deletions(-)
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -2559,12 +2559,26 @@ static void kvm_s390_set_crycb_format(st
kvm->arch.crypto.crycbd |= CRYCB_FORMAT1;
}
+/*
+ * kvm_arch_crypto_set_masks
+ *
+ * @kvm: pointer to the target guest's KVM struct containing the crypto masks
+ * to be set.
+ * @apm: the mask identifying the accessible AP adapters
+ * @aqm: the mask identifying the accessible AP domains
+ * @adm: the mask identifying the accessible AP control domains
+ *
+ * Set the masks that identify the adapters, domains and control domains to
+ * which the KVM guest is granted access.
+ *
+ * Note: The kvm->lock mutex must be locked by the caller before invoking this
+ * function.
+ */
void kvm_arch_crypto_set_masks(struct kvm *kvm, unsigned long *apm,
unsigned long *aqm, unsigned long *adm)
{
struct kvm_s390_crypto_cb *crycb = kvm->arch.crypto.crycb;
- mutex_lock(&kvm->lock);
kvm_s390_vcpu_block_all(kvm);
switch (kvm->arch.crypto.crycbd & CRYCB_FORMAT_MASK) {
@@ -2595,13 +2609,23 @@ void kvm_arch_crypto_set_masks(struct kv
/* recreate the shadow crycb for each vcpu */
kvm_s390_sync_request_broadcast(kvm, KVM_REQ_VSIE_RESTART);
kvm_s390_vcpu_unblock_all(kvm);
- mutex_unlock(&kvm->lock);
}
EXPORT_SYMBOL_GPL(kvm_arch_crypto_set_masks);
+/*
+ * kvm_arch_crypto_clear_masks
+ *
+ * @kvm: pointer to the target guest's KVM struct containing the crypto masks
+ * to be cleared.
+ *
+ * Clear the masks that identify the adapters, domains and control domains to
+ * which the KVM guest is granted access.
+ *
+ * Note: The kvm->lock mutex must be locked by the caller before invoking this
+ * function.
+ */
void kvm_arch_crypto_clear_masks(struct kvm *kvm)
{
- mutex_lock(&kvm->lock);
kvm_s390_vcpu_block_all(kvm);
memset(&kvm->arch.crypto.crycb->apcb0, 0,
@@ -2613,7 +2637,6 @@ void kvm_arch_crypto_clear_masks(struct
/* recreate the shadow crycb for each vcpu */
kvm_s390_sync_request_broadcast(kvm, KVM_REQ_VSIE_RESTART);
kvm_s390_vcpu_unblock_all(kvm);
- mutex_unlock(&kvm->lock);
}
EXPORT_SYMBOL_GPL(kvm_arch_crypto_clear_masks);
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -295,15 +295,6 @@ static int handle_pqap(struct kvm_vcpu *
matrix_mdev = container_of(vcpu->kvm->arch.crypto.pqap_hook,
struct ap_matrix_mdev, pqap_hook);
- /*
- * If the KVM pointer is in the process of being set, wait until the
- * process has completed.
- */
- wait_event_cmd(matrix_mdev->wait_for_kvm,
- !matrix_mdev->kvm_busy,
- mutex_unlock(&matrix_dev->lock),
- mutex_lock(&matrix_dev->lock));
-
/* If the there is no guest using the mdev, there is nothing to do */
if (!matrix_mdev->kvm)
goto out_unlock;
@@ -351,7 +342,6 @@ static int vfio_ap_mdev_create(struct md
matrix_mdev->mdev = mdev;
vfio_ap_matrix_init(&matrix_dev->info, &matrix_mdev->matrix);
- init_waitqueue_head(&matrix_mdev->wait_for_kvm);
mdev_set_drvdata(mdev, matrix_mdev);
matrix_mdev->pqap_hook = handle_pqap;
mutex_lock(&matrix_dev->lock);
@@ -618,11 +608,8 @@ static ssize_t assign_adapter_store(stru
mutex_lock(&matrix_dev->lock);
- /*
- * If the KVM pointer is in flux or the guest is running, disallow
- * un-assignment of adapter
- */
- if (matrix_mdev->kvm_busy || matrix_mdev->kvm) {
+ /* If the KVM guest is running, disallow assignment of adapter */
+ if (matrix_mdev->kvm) {
ret = -EBUSY;
goto done;
}
@@ -689,11 +676,8 @@ static ssize_t unassign_adapter_store(st
mutex_lock(&matrix_dev->lock);
- /*
- * If the KVM pointer is in flux or the guest is running, disallow
- * un-assignment of adapter
- */
- if (matrix_mdev->kvm_busy || matrix_mdev->kvm) {
+ /* If the KVM guest is running, disallow unassignment of adapter */
+ if (matrix_mdev->kvm) {
ret = -EBUSY;
goto done;
}
@@ -778,11 +762,8 @@ static ssize_t assign_domain_store(struc
mutex_lock(&matrix_dev->lock);
- /*
- * If the KVM pointer is in flux or the guest is running, disallow
- * assignment of domain
- */
- if (matrix_mdev->kvm_busy || matrix_mdev->kvm) {
+ /* If the KVM guest is running, disallow assignment of domain */
+ if (matrix_mdev->kvm) {
ret = -EBUSY;
goto done;
}
@@ -844,11 +825,8 @@ static ssize_t unassign_domain_store(str
mutex_lock(&matrix_dev->lock);
- /*
- * If the KVM pointer is in flux or the guest is running, disallow
- * un-assignment of domain
- */
- if (matrix_mdev->kvm_busy || matrix_mdev->kvm) {
+ /* If the KVM guest is running, disallow unassignment of domain */
+ if (matrix_mdev->kvm) {
ret = -EBUSY;
goto done;
}
@@ -897,11 +875,8 @@ static ssize_t assign_control_domain_sto
mutex_lock(&matrix_dev->lock);
- /*
- * If the KVM pointer is in flux or the guest is running, disallow
- * assignment of control domain.
- */
- if (matrix_mdev->kvm_busy || matrix_mdev->kvm) {
+ /* If the KVM guest is running, disallow assignment of control domain */
+ if (matrix_mdev->kvm) {
ret = -EBUSY;
goto done;
}
@@ -954,11 +929,8 @@ static ssize_t unassign_control_domain_s
mutex_lock(&matrix_dev->lock);
- /*
- * If the KVM pointer is in flux or the guest is running, disallow
- * un-assignment of control domain.
- */
- if (matrix_mdev->kvm_busy || matrix_mdev->kvm) {
+ /* If a KVM guest is running, disallow unassignment of control domain */
+ if (matrix_mdev->kvm) {
ret = -EBUSY;
goto done;
}
@@ -1097,28 +1069,30 @@ static int vfio_ap_mdev_set_kvm(struct a
struct ap_matrix_mdev *m;
if (kvm->arch.crypto.crycbd) {
+ down_write(&kvm->arch.crypto.pqap_hook_rwsem);
+ kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
+ up_write(&kvm->arch.crypto.pqap_hook_rwsem);
+
+ mutex_lock(&kvm->lock);
+ mutex_lock(&matrix_dev->lock);
+
list_for_each_entry(m, &matrix_dev->mdev_list, node) {
- if (m != matrix_mdev && m->kvm == kvm)
+ if (m != matrix_mdev && m->kvm == kvm) {
+ mutex_unlock(&kvm->lock);
+ mutex_unlock(&matrix_dev->lock);
return -EPERM;
+ }
}
kvm_get_kvm(kvm);
matrix_mdev->kvm = kvm;
- matrix_mdev->kvm_busy = true;
- mutex_unlock(&matrix_dev->lock);
-
- down_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem);
- kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
- up_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem);
-
kvm_arch_crypto_set_masks(kvm,
matrix_mdev->matrix.apm,
matrix_mdev->matrix.aqm,
matrix_mdev->matrix.adm);
- mutex_lock(&matrix_dev->lock);
- matrix_mdev->kvm_busy = false;
- wake_up_all(&matrix_mdev->wait_for_kvm);
+ mutex_unlock(&kvm->lock);
+ mutex_unlock(&matrix_dev->lock);
}
return 0;
@@ -1167,35 +1141,24 @@ static int vfio_ap_mdev_iommu_notifier(s
* certain circumstances, will result in a circular lock dependency if this is
* done under the @matrix_mdev->lock.
*/
-static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev)
+static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev,
+ struct kvm *kvm)
{
- /*
- * If the KVM pointer is in the process of being set, wait until the
- * process has completed.
- */
- wait_event_cmd(matrix_mdev->wait_for_kvm,
- !matrix_mdev->kvm_busy,
- mutex_unlock(&matrix_dev->lock),
- mutex_lock(&matrix_dev->lock));
-
- if (matrix_mdev->kvm) {
- matrix_mdev->kvm_busy = true;
- mutex_unlock(&matrix_dev->lock);
-
- if (matrix_mdev->kvm->arch.crypto.crycbd) {
- down_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem);
- matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
- up_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem);
-
- kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
- }
+ if (kvm && kvm->arch.crypto.crycbd) {
+ down_write(&kvm->arch.crypto.pqap_hook_rwsem);
+ kvm->arch.crypto.pqap_hook = NULL;
+ up_write(&kvm->arch.crypto.pqap_hook_rwsem);
+ mutex_lock(&kvm->lock);
mutex_lock(&matrix_dev->lock);
+
+ kvm_arch_crypto_clear_masks(kvm);
vfio_ap_mdev_reset_queues(matrix_mdev->mdev);
- kvm_put_kvm(matrix_mdev->kvm);
+ kvm_put_kvm(kvm);
matrix_mdev->kvm = NULL;
- matrix_mdev->kvm_busy = false;
- wake_up_all(&matrix_mdev->wait_for_kvm);
+
+ mutex_unlock(&kvm->lock);
+ mutex_unlock(&matrix_dev->lock);
}
}
@@ -1208,16 +1171,13 @@ static int vfio_ap_mdev_group_notifier(s
if (action != VFIO_GROUP_NOTIFY_SET_KVM)
return NOTIFY_OK;
- mutex_lock(&matrix_dev->lock);
matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier);
if (!data)
- vfio_ap_mdev_unset_kvm(matrix_mdev);
+ vfio_ap_mdev_unset_kvm(matrix_mdev, matrix_mdev->kvm);
else if (vfio_ap_mdev_set_kvm(matrix_mdev, data))
notify_rc = NOTIFY_DONE;
- mutex_unlock(&matrix_dev->lock);
-
return notify_rc;
}
@@ -1351,14 +1311,11 @@ static void vfio_ap_mdev_close_device(st
{
struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
- mutex_lock(&matrix_dev->lock);
- vfio_ap_mdev_unset_kvm(matrix_mdev);
- mutex_unlock(&matrix_dev->lock);
-
vfio_unregister_notifier(mdev_dev(mdev), VFIO_IOMMU_NOTIFY,
&matrix_mdev->iommu_notifier);
vfio_unregister_notifier(mdev_dev(mdev), VFIO_GROUP_NOTIFY,
&matrix_mdev->group_notifier);
+ vfio_ap_mdev_unset_kvm(matrix_mdev, matrix_mdev->kvm);
module_put(THIS_MODULE);
}
@@ -1400,15 +1357,6 @@ static ssize_t vfio_ap_mdev_ioctl(struct
break;
}
- /*
- * If the KVM pointer is in the process of being set, wait until
- * the process has completed.
- */
- wait_event_cmd(matrix_mdev->wait_for_kvm,
- !matrix_mdev->kvm_busy,
- mutex_unlock(&matrix_dev->lock),
- mutex_lock(&matrix_dev->lock));
-
ret = vfio_ap_mdev_reset_queues(mdev);
break;
default:
--- a/drivers/s390/crypto/vfio_ap_private.h
+++ b/drivers/s390/crypto/vfio_ap_private.h
@@ -83,8 +83,6 @@ struct ap_matrix_mdev {
struct ap_matrix matrix;
struct notifier_block group_notifier;
struct notifier_block iommu_notifier;
- bool kvm_busy;
- wait_queue_head_t wait_for_kvm;
struct kvm *kvm;
crypto_hook pqap_hook;
struct mdev_device *mdev;