Commit 5c73b9a2 authored Jul 20, 2020 by Ahmed S. Darwish Committed by Peter Zijlstra Jul 29, 2020

kvm/eventfd: Use sequence counter with associated spinlock



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

parent 2ca97ac8

include/linux/kvm_irqfd.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -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;

virt/kvm/eventfd.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -303,7 +303,7 @@ kvm_irqfd_assign(struct kvm kvm, struct kvm_irqfd args)
		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) {

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