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From: Jason Wang <jasowang@redhat.com>
To: mst@redhat.com, jasowang@redhat.com, kvm@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, jgg@ziepe.ca
Subject: [PATCH V2 6/9] vhost: don't do synchronize_rcu() in vhost_uninit_vq_maps()
Date: Wed, 31 Jul 2019 04:46:52 -0400	[thread overview]
Message-ID: <20190731084655.7024-7-jasowang@redhat.com> (raw)
In-Reply-To: <20190731084655.7024-1-jasowang@redhat.com>

There's no need for RCU synchronization in vhost_uninit_vq_maps()
since we've already serialized with readers (memory accessors). This
also avoid the possible userspace DOS through ioctl() because of the
possible high latency caused by synchronize_rcu().

Reported-by: Michael S. Tsirkin <mst@redhat.com>
Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual address")
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 drivers/vhost/vhost.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index c12cdadb0855..cfc11f9ed9c9 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -333,7 +333,9 @@ static void vhost_uninit_vq_maps(struct vhost_virtqueue *vq)
 	}
 	spin_unlock(&vq->mmu_lock);
 
-	synchronize_rcu();
+	/* No need for synchronize_rcu() or kfree_rcu() since we are
+	 * serialized with memory accessors (e.g vq mutex held).
+	 */
 
 	for (i = 0; i < VHOST_NUM_ADDRS; i++)
 		if (map[i])
-- 
2.18.1


  parent reply	other threads:[~2019-07-31  8:47 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-31  8:46 [PATCH V2 0/9] Fixes for metadata accelreation Jason Wang
2019-07-31  8:46 ` [PATCH V2 1/9] vhost: don't set uaddr for invalid address Jason Wang
2019-07-31  8:46 ` [PATCH V2 2/9] vhost: validate MMU notifier registration Jason Wang
2019-07-31  8:46 ` [PATCH V2 3/9] vhost: fix vhost map leak Jason Wang
2019-07-31  8:46 ` [PATCH V2 4/9] vhost: reset invalidate_count in vhost_set_vring_num_addr() Jason Wang
2019-07-31 12:41   ` Jason Gunthorpe
2019-07-31 13:29     ` Jason Wang
2019-07-31 19:32       ` Jason Gunthorpe
2019-07-31 19:37         ` Michael S. Tsirkin
2019-08-01  5:03         ` Jason Wang
2019-07-31  8:46 ` [PATCH V2 5/9] vhost: mark dirty pages during map uninit Jason Wang
2019-07-31  8:46 ` Jason Wang [this message]
2019-07-31  8:46 ` [PATCH V2 7/9] vhost: do not use RCU to synchronize MMU notifier with worker Jason Wang
2019-07-31  8:50   ` Jason Wang
2019-07-31 12:39   ` Jason Gunthorpe
2019-07-31 13:28     ` Jason Wang
2019-07-31 19:30       ` Jason Gunthorpe
2019-08-01  5:02         ` Jason Wang
2019-08-01 14:15           ` Jason Gunthorpe
2019-08-02  9:40             ` Jason Wang
2019-08-02 12:46               ` Jason Gunthorpe
2019-08-02 14:27                 ` Michael S. Tsirkin
2019-08-02 17:24                   ` Jason Gunthorpe
2019-08-03 21:36                     ` Michael S. Tsirkin
2019-08-04  0:14                       ` Jason Gunthorpe
2019-08-04  8:07                         ` Michael S. Tsirkin
2019-08-05  4:39                           ` Jason Wang
2019-08-06 11:53                           ` Jason Gunthorpe
2019-08-06 13:36                             ` Michael S. Tsirkin
2019-08-06 13:40                               ` Jason Gunthorpe
2019-08-05  4:36                   ` Jason Wang
2019-08-05  4:41                     ` Jason Wang
2019-08-05  6:40                       ` Michael S. Tsirkin
2019-08-05  8:24                         ` Jason Wang
2019-08-05  6:30                     ` Michael S. Tsirkin
2019-08-05  8:22                       ` Jason Wang
2019-08-05  4:20                 ` Jason Wang
2019-08-06 12:04                   ` Jason Gunthorpe
2019-08-07  6:49                     ` Jason Wang
2019-08-02 14:03               ` Michael S. Tsirkin
2019-08-05  4:33                 ` Jason Wang
2019-08-05  6:28                   ` Michael S. Tsirkin
2019-08-05  8:21                     ` Jason Wang
2019-07-31 18:29   ` Michael S. Tsirkin
2019-08-01  8:06     ` Jason Wang
2019-08-03 21:54       ` Michael S. Tsirkin
2019-08-05  8:18         ` Jason Wang
2019-07-31  8:46 ` [PATCH V2 8/9] vhost: correctly set dirty pages in MMU notifiers callback Jason Wang
2019-07-31  8:46 ` [PATCH V2 9/9] vhost: do not return -EAGIAN for non blocking invalidation too early Jason Wang
2019-07-31  9:59   ` Stefano Garzarella
2019-07-31 10:05     ` Jason Wang

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