linux-kernel - [PATCH 03/12] KVM: Initialize irqfd waitqueue callback when adding to the queue

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Message-ID: <20250401204425.904001-4-seanjc@google.com>
Date: Tue,  1 Apr 2025 13:44:15 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Ingo Molnar <mingo@...hat.com>, 
	Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>, 
	Vincent Guittot <vincent.guittot@...aro.org>, Marc Zyngier <maz@...nel.org>, 
	Oliver Upton <oliver.upton@...ux.dev>, Sean Christopherson <seanjc@...gle.com>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Albert Ou <aou@...s.berkeley.edu>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
	linux-riscv@...ts.infradead.org, David Matlack <dmatlack@...gle.com>, 
	Juergen Gross <jgross@...e.com>, Stefano Stabellini <sstabellini@...nel.org>, 
	Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Subject: [PATCH 03/12] KVM: Initialize irqfd waitqueue callback when adding to
 the queue

Initialize the irqfd waitqueue callback immediately prior to inserting the
irqfd into the eventfd's waitqueue.  Pre-initializing the state in a
completely different context is all kinds of confusing, and incorrectly
suggests that the waitqueue function needs to be initialize prior to
vfs_poll().

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 virt/kvm/eventfd.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index e47b7b6df94f..69bf2881635e 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -256,6 +256,13 @@ static void kvm_irqfd_register(struct file *file, wait_queue_head_t *wqh,
 	struct kvm_irqfd_pt *p = container_of(pt, struct kvm_irqfd_pt, pt);
 	struct kvm_kernel_irqfd *irqfd = p->irqfd;
 
+	/*
+	 * Add the irqfd as a priority waiter on the eventfd, with a custom
+	 * wake-up handler, so that KVM *and only KVM* is notified whenever the
+	 * underlying eventfd is signaled.
+	 */
+	init_waitqueue_func_entry(&irqfd->wait, irqfd_wakeup);
+
 	add_wait_queue_priority(wqh, &irqfd->wait);
 }
 
@@ -395,12 +402,6 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
 		mutex_unlock(&kvm->irqfds.resampler_lock);
 	}
 
-	/*
-	 * Install our own custom wake-up handling so we are notified via
-	 * a callback whenever someone signals the underlying eventfd
-	 */
-	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
-- 
2.49.0.504.g3bcea36a83-goog