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Fri, 3 Jul 2020 10:07:43 +0000 (UTC) Received: from localhost (ovpn-113-54.ams2.redhat.com [10.36.113.54]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 48B1B7BD56; Fri, 3 Jul 2020 10:07:43 +0000 (UTC) From: Cornelia Huck To: Peter Maydell Subject: [PULL 14/14] s390x/pci: fix set_ind_atomic Date: Fri, 3 Jul 2020 12:06:50 +0200 Message-Id: <20200703100650.621212-15-cohuck@redhat.com> In-Reply-To: <20200703100650.621212-1-cohuck@redhat.com> References: <20200703100650.621212-1-cohuck@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=cohuck@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Received-SPF: pass client-ip=205.139.110.61; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/03 03:17:33 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Halil Pasic , Christian Borntraeger , qemu-s390x@nongnu.org, Cornelia Huck , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" From: Halil Pasic 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. Let us use volatile to force the rules of the abstract machine for accesses to *ind_addr. Let us also rewrite the loop so, we that the new old is used to compute the new desired value if the xchg part is not performed. Fixes: 8cba80c3a0 ("s390: Add PCI bus support") Reported-by: Christian Borntraeger Signed-off-by: Halil Pasic Reviewed-by: Christian Borntraeger Message-Id: <20200616045035.51641-3-pasic@linux.ibm.com> Signed-off-by: Cornelia Huck --- hw/s390x/s390-pci-bus.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c index 142e52a8ffdd..736965c9287f 100644 --- a/hw/s390x/s390-pci-bus.c +++ b/hw/s390x/s390-pci-bus.c @@ -637,22 +637,24 @@ static AddressSpace *s390_pci_dma_iommu(PCIBus *bus, void *opaque, int devfn) static uint8_t set_ind_atomic(uint64_t ind_loc, uint8_t to_be_set) { - uint8_t ind_old, ind_new; + uint8_t expected, actual; hwaddr len = 1; - uint8_t *ind_addr; + /* avoid multiple fetches */ + uint8_t volatile *ind_addr; ind_addr = cpu_physical_memory_map(ind_loc, &len, true); if (!ind_addr) { s390_pci_generate_error_event(ERR_EVENT_AIRERR, 0, 0, 0, 0); return -1; } + actual = *ind_addr; do { - ind_old = *ind_addr; - ind_new = ind_old | to_be_set; - } while (atomic_cmpxchg(ind_addr, ind_old, ind_new) != ind_old); - cpu_physical_memory_unmap(ind_addr, len, 1, len); + expected = actual; + actual = atomic_cmpxchg(ind_addr, expected, expected | to_be_set); + } while (actual != expected); + cpu_physical_memory_unmap((void *)ind_addr, len, 1, len); - return ind_old; + return actual; } static void s390_msi_ctrl_write(void *opaque, hwaddr addr, uint64_t data,