diff options
| author | Sean Christopherson <seanjc@google.com> | 2025-05-22 16:52:12 -0700 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2025-06-23 09:50:54 -0700 |
| commit | 140768a7bf03df2a746cdbd4b6dc938d80caad8d (patch) | |
| tree | 67469cd2a2f41f34b019397d60e1addb317b123a | |
| parent | 283ed5001d6852f85c09ed2522331b2b197ba937 (diff) | |
KVM: Acquire SCRU lock outside of irqfds.lock during assignment
Acquire SRCU outside of irqfds.lock so that the locking is symmetrical,
and add a comment explaining why on earth KVM holds SRCU for so long.
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250522235223.3178519-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
| -rw-r--r-- | virt/kvm/eventfd.c | 19 |
1 files changed, 16 insertions, 3 deletions
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c index 0b655376734e..614f81cd37c1 100644 --- a/virt/kvm/eventfd.c +++ b/virt/kvm/eventfd.c @@ -394,6 +394,18 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) */ init_waitqueue_func_entry(&irqfd->wait, irqfd_wakeup); + /* + * Set the irqfd routing and add it to KVM's list before registering + * the irqfd with the eventfd, so that the routing information is valid + * and stays valid, e.g. if there are GSI routing changes, prior to + * making the irqfd visible, i.e. before it might be signaled. + * + * Note, holding SRCU ensures a stable read of routing information, and + * also prevents irqfd_shutdown() from freeing the irqfd before it's + * fully initialized. + */ + idx = srcu_read_lock(&kvm->irq_srcu); + spin_lock_irq(&kvm->irqfds.lock); ret = 0; @@ -402,11 +414,9 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) continue; /* This fd is used for another irq already. */ ret = -EBUSY; - spin_unlock_irq(&kvm->irqfds.lock); - goto fail; + goto fail_duplicate; } - idx = srcu_read_lock(&kvm->irq_srcu); irqfd_update(kvm, irqfd); list_add_tail(&irqfd->list, &kvm->irqfds.items); @@ -441,6 +451,9 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) srcu_read_unlock(&kvm->irq_srcu, idx); return 0; +fail_duplicate: + spin_unlock_irq(&kvm->irqfds.lock); + srcu_read_unlock(&kvm->irq_srcu, idx); fail: if (irqfd->resampler) irqfd_resampler_shutdown(irqfd); |