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KVM: irqfd: Make resampler_list an RCU list

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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>
This commit is contained in:
Dmytro Maluka 2023-03-22 21:43:43 +01:00 committed by Paolo Bonzini
parent e5c972c1fa
commit d583fbd706
3 changed files with 8 additions and 3 deletions
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1
include/linux/kvm_host.h
View File

@ -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;

2
include/linux/kvm_irqfd.h
View File

@ -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;
};

8
virt/kvm/eventfd.c
View File

@ -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;