It is useful to be able to do read-only traversal of the list of all the
registered irqfd resamplers without locking the resampler_lock mutex.
In particular, we are going to traverse it to search for a resampler
registered for the given irq of an irqchip, and that will be done with
an irqchip spinlock (ioapic->lock) held, so it is undesirable to lock a
mutex in this context. So turn this list into an RCU list.
For protecting the read side, reuse kvm->irq_srcu which is already used
for protecting a number of irq related things (kvm->irq_routing,
irqfd->resampler->list, kvm->irq_ack_notifier_list,
kvm->arch.mask_notifier_list).
Signed-off-by: Dmytro Maluka <dmy@xxxxxxxxxxxx>
---
include/linux/kvm_host.h | 1 +
include/linux/kvm_irqfd.h | 2 +-
virt/kvm/eventfd.c | 8 ++++++--
3 files changed, 8 insertions(+), 3 deletions(-)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 8ada23756b0e..9f508c8e66e1 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -755,6 +755,7 @@ struct kvm {
struct {
spinlock_t lock;
struct list_head items;
+ /* resampler_list update side is protected by resampler_lock. */
struct list_head resampler_list;
struct mutex resampler_lock;
} irqfds;
diff --git a/include/linux/kvm_irqfd.h b/include/linux/kvm_irqfd.h
index dac047abdba7..8ad43692e3bb 100644
--- a/include/linux/kvm_irqfd.h
+++ b/include/linux/kvm_irqfd.h
@@ -31,7 +31,7 @@ struct kvm_kernel_irqfd_resampler {
/*
* Entry in list of kvm->irqfd.resampler_list. Use for sharing
* resamplers among irqfds on the same gsi.
- * Accessed and modified under kvm->irqfds.resampler_lock
+ * RCU list modified under kvm->irqfds.resampler_lock
*/
struct list_head link;
};
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 2a3ed401ce46..61aea70dd888 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -96,8 +96,12 @@ irqfd_resampler_shutdown(struct kvm_kernel_irqfd *irqfd)
synchronize_srcu(&kvm->irq_srcu);
if (list_empty(&resampler->list)) {
- list_del(&resampler->link);
+ list_del_rcu(&resampler->link);
kvm_unregister_irq_ack_notifier(kvm, &resampler->notifier);
+ /*
+ * synchronize_srcu(&kvm->irq_srcu) already called
+ * in kvm_unregister_irq_ack_notifier().
+ */
kvm_set_irq(kvm, KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID,
resampler->notifier.gsi, 0, false);
kfree(resampler);
@@ -369,7 +373,7 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
resampler->notifier.irq_acked = irqfd_resampler_ack;
INIT_LIST_HEAD(&resampler->link);
- list_add(&resampler->link, &kvm->irqfds.resampler_list);
+ list_add_rcu(&resampler->link, &kvm->irqfds.resampler_list);
kvm_register_irq_ack_notifier(kvm,
&resampler->notifier);
irqfd->resampler = resampler;
--
2.40.0.348.gf938b09366-goog
