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From: Christian Borntraeger <borntraeger@de.ibm.com>
To: "Michael S. Tsirkin" <mst@redhat.com>, Halil Pasic <pasic@linux.ibm.com>
Cc: Thomas Huth <thuth@redhat.com>,
	Matthew Rosato <mjrosato@linux.ibm.com>,
	David Hildenbrand <david@redhat.com>,
	Cornelia Huck <cohuck@redhat.com>,
	qemu-devel@nongnu.org, qemu-s390x@nongnu.org,
	Richard Henderson <rth@twiddle.net>
Subject: Re: [PATCH 1/2] virtio-ccw: fix virtio_set_ind_atomic
Date: Mon, 6 Jul 2020 07:44:59 +0200
Message-ID: <94c5c857-c3bc-3829-7d8e-e99405b83061@de.ibm.com> (raw)
In-Reply-To: <20200704143126-mutt-send-email-mst@kernel.org>



On 04.07.20 20:34, Michael S. Tsirkin wrote:
> On Tue, Jun 16, 2020 at 06:50:34AM +0200, Halil Pasic wrote:
>> The atomic_cmpxchg() loop is broken because we occasionally end up with
>> old and _old having different values (a legit compiler can generate code
>> that accessed *ind_addr again to pick up a value for _old instead of
>> using the value of old that was already fetched according to the
>> rules of the abstract machine). This means the underlying CS instruction
>> may use a different old (_old) than the one we intended to use if
>> atomic_cmpxchg() performed the xchg part.
> 
> And was this ever observed in the field? Or is this a theoretical issue?
> commit log should probably say ...

It was observed in the field when the xml specified qemu instead of vhost.


  reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-16  4:50 [PATCH 0/2] two atomic_cmpxchg() related fixes Halil Pasic
2020-06-16  4:50 ` [PATCH 1/2] virtio-ccw: fix virtio_set_ind_atomic Halil Pasic
2020-06-16  5:58   ` Christian Borntraeger
2020-06-16  6:33     ` Cornelia Huck
2020-06-16  6:45       ` Christian Borntraeger
2020-06-19  7:14         ` Cornelia Huck
2020-06-17 23:56       ` Halil Pasic
2020-06-19  7:33         ` David Hildenbrand
2020-06-19  8:17           ` Halil Pasic
2020-06-16  9:31     ` Halil Pasic
2020-07-01 13:13   ` Christian Borntraeger
2020-07-04 18:34   ` Michael S. Tsirkin
2020-07-06  5:44     ` Christian Borntraeger [this message]
2020-07-06 11:19     ` Halil Pasic
2020-06-16  4:50 ` [PATCH 2/2] s390x/pci: fix set_ind_atomic Halil Pasic
2020-07-01 13:14   ` Christian Borntraeger
2020-07-01 12:01 ` [PATCH 0/2] two atomic_cmpxchg() related fixes Cornelia Huck
2020-07-01 12:06   ` Christian Borntraeger
2020-07-01 13:10     ` Cornelia Huck
2020-07-03 13:37     ` Halil Pasic
2020-07-03 14:03       ` Cornelia Huck
2020-07-02 11:18 ` Cornelia Huck

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