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| author | Halil Pasic | 2020-06-16 06:50:35 +0200 |
|---|---|---|
| committer | Cornelia Huck | 2020-07-03 11:15:59 +0200 |
| commit | 45175361f1bfc2d3ccdcb4b22570c2352f3de754 (patch) | |
| tree | 411f7e555d907b421add6a2d3458e50f5319d3df /hw/s390x | |
| parent | virtio-ccw: fix virtio_set_ind_atomic (diff) | |
| download | qemu-45175361f1bfc2d3ccdcb4b22570c2352f3de754.tar.gz qemu-45175361f1bfc2d3ccdcb4b22570c2352f3de754.tar.xz qemu-45175361f1bfc2d3ccdcb4b22570c2352f3de754.zip | |
s390x/pci: fix set_ind_atomic
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 <borntraeger@de.ibm.com>
Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Message-Id: <20200616045035.51641-3-pasic@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Diffstat (limited to 'hw/s390x')
| -rw-r--r-- | hw/s390x/s390-pci-bus.c | 16 |
1 files changed, 9 insertions, 7 deletions
diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c index 142e52a8ff..736965c928 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, |