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bh=YfVEVmjau3G6Kev/27aLeUkr71n8IWpHubQtmPsf6WQ=; b=Vv2Zrnq3PcgObNtwskWJDLIQWgoZebrQebTF2tXH+m5e8DOQmh3GgUlMWsYd9KGzBK4QOa pn3GclqVSok6AWLUzpTbMdQm/2q7tEAZ/6D7y3xp4BeO4QtT/7gMJc63OWzfMDeJ2bYqoF FFefD2tEhZ04JL6D1mzgebaquBOXFCY= X-MC-Unique: TEqoii_7NXytrLAvgyd-7g-1 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 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; 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charset="utf-8" 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) =20 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 =3D 1; - uint8_t *ind_addr; + /* avoid multiple fetches */ + uint8_t volatile *ind_addr; =20 ind_addr =3D 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 =3D *ind_addr; do { - ind_old =3D *ind_addr; - ind_new =3D ind_old | to_be_set; - } while (atomic_cmpxchg(ind_addr, ind_old, ind_new) !=3D ind_old); - cpu_physical_memory_unmap(ind_addr, len, 1, len); + expected =3D actual; + actual =3D atomic_cmpxchg(ind_addr, expected, expected | to_be_set= ); + } while (actual !=3D expected); + cpu_physical_memory_unmap((void *)ind_addr, len, 1, len); =20 - return ind_old; + return actual; } =20 static void s390_msi_ctrl_write(void *opaque, hwaddr addr, uint64_t data, --=20 2.25.4