linux-kernel - [PATCH 01/12] KVM: Use a local struct to do the initial vfs

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Message-ID: <20250401204425.904001-2-seanjc@google.com>
Date: Tue,  1 Apr 2025 13:44:13 -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 01/12] KVM: Use a local struct to do the initial vfs_poll() on
 an irqfd

Use a function-local struct for the poll_table passted to vfs_poll(), as
nothing in the vfs_poll() callchain grabs a long-term reference to the
structure, i.e. its lifetime doesn't need to be tied to the irqfd.  Using
a local structure will also allow propagating failures out of the polling
callback without further polluting kvm_kernel_irqfd.

Opportunstically rename irqfd_ptable_queue_proc() to kvm_irqfd_register()
to capture what it actually does.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 include/linux/kvm_irqfd.h |  1 -
 virt/kvm/eventfd.c        | 26 +++++++++++++++++---------
 2 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/include/linux/kvm_irqfd.h b/include/linux/kvm_irqfd.h
index 8ad43692e3bb..44fd2a20b09e 100644
--- a/include/linux/kvm_irqfd.h
+++ b/include/linux/kvm_irqfd.h
@@ -55,7 +55,6 @@ struct kvm_kernel_irqfd {
 	/* Used for setup/shutdown */
 	struct eventfd_ctx *eventfd;
 	struct list_head list;
-	poll_table pt;
 	struct work_struct shutdown;
 	struct irq_bypass_consumer consumer;
 	struct irq_bypass_producer *producer;
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 249ba5b72e9b..01c6eb4dceb8 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -245,12 +245,17 @@ irqfd_wakeup(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
 	return ret;
 }
 
-static void
-irqfd_ptable_queue_proc(struct file *file, wait_queue_head_t *wqh,
-			poll_table *pt)
+struct kvm_irqfd_pt {
+	struct kvm_kernel_irqfd *irqfd;
+	poll_table pt;
+};
+
+static void kvm_irqfd_register(struct file *file, wait_queue_head_t *wqh,
+			       poll_table *pt)
 {
-	struct kvm_kernel_irqfd *irqfd =
-		container_of(pt, struct kvm_kernel_irqfd, pt);
+	struct kvm_irqfd_pt *p = container_of(pt, struct kvm_irqfd_pt, pt);
+	struct kvm_kernel_irqfd *irqfd = p->irqfd;
+
 	add_wait_queue_priority(wqh, &irqfd->wait);
 }
 
@@ -305,6 +310,7 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
 {
 	struct kvm_kernel_irqfd *irqfd, *tmp;
 	struct eventfd_ctx *eventfd = NULL, *resamplefd = NULL;
+	struct kvm_irqfd_pt irqfd_pt;
 	int ret;
 	__poll_t events;
 	int idx;
@@ -394,7 +400,6 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
 	 * a callback whenever someone signals the underlying eventfd
 	 */
 	init_waitqueue_func_entry(&irqfd->wait, irqfd_wakeup);
-	init_poll_funcptr(&irqfd->pt, irqfd_ptable_queue_proc);
 
 	spin_lock_irq(&kvm->irqfds.lock);
 
@@ -416,11 +421,14 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
 	spin_unlock_irq(&kvm->irqfds.lock);
 
 	/*
-	 * Check if there was an event already pending on the eventfd
-	 * before we registered, and trigger it as if we didn't miss it.
+	 * Register the irqfd with the eventfd by polling on the eventfd.  If
+	 * there was en event pending on the eventfd prior to registering,
+	 * manually trigger IRQ injection.
 	 */
-	events = vfs_poll(fd_file(f), &irqfd->pt);
+	irqfd_pt.irqfd = irqfd;
+	init_poll_funcptr(&irqfd_pt.pt, kvm_irqfd_register);
 
+	events = vfs_poll(fd_file(f), &irqfd_pt.pt);
 	if (events & EPOLLIN)
 		schedule_work(&irqfd->inject);
 
-- 
2.49.0.504.g3bcea36a83-goog