From: "Ahmed S. Darwish" <a.darwish@linutronix.de>
Date: Mon, 20 Jul 2020 17:55:29 +0200
Subject: kvm/eventfd: Use sequence counter with associated spinlock
Patch-mainline: v5.9-rc1
Git-commit: 5c73b9a2b1b4ecc809a914aa64970157b3d8c936
References: bsc#1176564 bsc#1162702

A sequence counter write side critical section must be protected by some
form of locking to serialize writers. A plain seqcount_t does not
contain the information of which lock must be held when entering a write
side critical section.

Use the new seqcount_spinlock_t data type, which allows to associate a
spinlock with the sequence counter. This enables lockdep to verify that
the spinlock used for writer serialization is held when the write side
critical section is entered.

If lockdep is disabled this lock association is compiled out and has
neither storage size nor runtime overhead.

Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lkml.kernel.org/r/20200720155530.1173732-24-a.darwish@linutronix.de
Acked-by: Daniel Wagner <dwagner@suse.de>
---
 include/linux/kvm_irqfd.h |    2 +-
 virt/kvm/eventfd.c        |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

--- a/include/linux/kvm_irqfd.h
+++ b/include/linux/kvm_irqfd.h
@@ -42,7 +42,7 @@ struct kvm_kernel_irqfd {
 	wait_queue_entry_t wait;
 	/* Update side is protected by irqfds.lock */
 	struct kvm_kernel_irq_routing_entry irq_entry;
-	seqcount_t irq_entry_sc;
+	seqcount_spinlock_t irq_entry_sc;
 	/* Used for level IRQ fast-path */
 	int gsi;
 	struct work_struct inject;
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -303,7 +303,7 @@ kvm_irqfd_assign(struct kvm *kvm, struct
 	INIT_LIST_HEAD(&irqfd->list);
 	INIT_WORK(&irqfd->inject, irqfd_inject);
 	INIT_WORK(&irqfd->shutdown, irqfd_shutdown);
-	seqcount_init(&irqfd->irq_entry_sc);
+	seqcount_spinlock_init(&irqfd->irq_entry_sc, &kvm->irqfds.lock);
 
 	f = fdget(args->fd);
 	if (!f.file) {