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authorDmytro Maluka <dmy@semihalf.com>2023-03-22 21:43:43 +0100
committerPaolo Bonzini <pbonzini@redhat.com>2023-03-27 10:13:28 -0400
commitd583fbd7066a2dea43050521a95d9770f7d7593e (patch)
tree4ced8cc1d8e18a2af60394d1f9bd7274e9d4d2c3
parente5c972c1fadacc858b6a564d056f177275238040 (diff)
KVM: irqfd: Make resampler_list an RCU list
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@semihalf.com> Message-Id: <20230322204344.50138-2-dmy@semihalf.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
-rw-r--r--include/linux/kvm_host.h1
-rw-r--r--include/linux/kvm_irqfd.h2
-rw-r--r--virt/kvm/eventfd.c8
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;