linux-kernel - [tip: locking/core] kvm/eventfd: Use sequence counter with associated spinlock

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Date:   Wed, 29 Jul 2020 14:33:27 -0000
From:   "tip-bot2 for Ahmed S. Darwish" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: locking/core] kvm/eventfd: Use sequence counter with associated
 spinlock

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     5c73b9a2b1b4ecc809a914aa64970157b3d8c936
Gitweb:        https://git.kernel.org/tip/5c73b9a2b1b4ecc809a914aa64970157b3d8c936
Author:        Ahmed S. Darwish <a.darwish@...utronix.de>
AuthorDate:    Mon, 20 Jul 2020 17:55:29 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 29 Jul 2020 16:14:29 +02:00

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

diff --git a/include/linux/kvm_irqfd.h b/include/linux/kvm_irqfd.h
index dc1da02..dac047a 100644
--- 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;
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index ef7ed91..d6408bb 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -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) {