hw/s390x/s390-pci-bus.c | 7 +++++++ 1 file changed, 7 insertions(+)
Hot-unplugging a vfio-pci device on s390x causes a QEMU crash:
qemu-system-s390x: ../softmmu/memory.c:2772:
do_address_space_destroy: Assertion `QTAILQ_EMPTY(&as->listeners)' failed.
In s390, the IOMMU address space is freed during device unplug but the
associated vfio-pci device may not yet be finalized and therefore may
still have a listener registered to the IOMMU address space.
Commit a2166410ad74 ("spapr_pci: Unregister listeners before destroying
the IOMMU address space") previously resolved this issue for spapr_pci.
We are now seeing this in s390x; it would seem the possibility for this
issue was already present but based on a bisect commit 2d24a6466154
("device-core: use RCU for list of children of a bus") has now changed
the timing such that it is now readily reproducible.
Add logic to ensure listeners are removed before destroying the address
space.
Reported-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
Reviewed-by: Pierre Morel <pmorel@linux.ibm.com>
Tested-by: Niklas Schnelle <schnelle@linux.ibm.com>
---
hw/s390x/s390-pci-bus.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
index 48a3be8..e0dc20c 100644
--- a/hw/s390x/s390-pci-bus.c
+++ b/hw/s390x/s390-pci-bus.c
@@ -732,6 +732,13 @@ static void s390_pci_iommu_free(S390pciState *s, PCIBus *bus, int32_t devfn)
table->iommu[PCI_SLOT(devfn)] = NULL;
g_hash_table_destroy(iommu->iotlb);
+ /*
+ * An attached PCI device may have memory listeners, eg. VFIO PCI.
+ * The associated subregion will already have been unmapped in
+ * s390_pci_iommu_disable in response to the guest deconfigure request.
+ * Remove the listeners now before destroying the address space.
+ */
+ address_space_remove_listeners(&iommu->as);
address_space_destroy(&iommu->as);
object_unparent(OBJECT(&iommu->mr));
object_unparent(OBJECT(iommu));
--
1.8.3.1
On 16/11/2020 22.42, Matthew Rosato wrote: > Hot-unplugging a vfio-pci device on s390x causes a QEMU crash: > > qemu-system-s390x: ../softmmu/memory.c:2772: > do_address_space_destroy: Assertion `QTAILQ_EMPTY(&as->listeners)' failed. > > In s390, the IOMMU address space is freed during device unplug but the > associated vfio-pci device may not yet be finalized and therefore may > still have a listener registered to the IOMMU address space. > > Commit a2166410ad74 ("spapr_pci: Unregister listeners before destroying > the IOMMU address space") previously resolved this issue for spapr_pci. > We are now seeing this in s390x; it would seem the possibility for this > issue was already present but based on a bisect commit 2d24a6466154 > ("device-core: use RCU for list of children of a bus") has now changed > the timing such that it is now readily reproducible. > > Add logic to ensure listeners are removed before destroying the address > space. > > Reported-by: Niklas Schnelle <schnelle@linux.ibm.com> > Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com> > Reviewed-by: Pierre Morel <pmorel@linux.ibm.com> > Tested-by: Niklas Schnelle <schnelle@linux.ibm.com> > --- > hw/s390x/s390-pci-bus.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c > index 48a3be8..e0dc20c 100644 > --- a/hw/s390x/s390-pci-bus.c > +++ b/hw/s390x/s390-pci-bus.c > @@ -732,6 +732,13 @@ static void s390_pci_iommu_free(S390pciState *s, PCIBus *bus, int32_t devfn) > > table->iommu[PCI_SLOT(devfn)] = NULL; > g_hash_table_destroy(iommu->iotlb); > + /* > + * An attached PCI device may have memory listeners, eg. VFIO PCI. > + * The associated subregion will already have been unmapped in > + * s390_pci_iommu_disable in response to the guest deconfigure request. > + * Remove the listeners now before destroying the address space. > + */ > + address_space_remove_listeners(&iommu->as); > address_space_destroy(&iommu->as); > object_unparent(OBJECT(&iommu->mr)); > object_unparent(OBJECT(iommu)); > Looks reasonable to me. Reviewed-by: Thomas Huth <thuth@redhat.com>
On Mon, 16 Nov 2020 16:42:35 -0500 Matthew Rosato <mjrosato@linux.ibm.com> wrote: > Hot-unplugging a vfio-pci device on s390x causes a QEMU crash: > > qemu-system-s390x: ../softmmu/memory.c:2772: > do_address_space_destroy: Assertion `QTAILQ_EMPTY(&as->listeners)' failed. > > In s390, the IOMMU address space is freed during device unplug but the > associated vfio-pci device may not yet be finalized and therefore may > still have a listener registered to the IOMMU address space. > > Commit a2166410ad74 ("spapr_pci: Unregister listeners before destroying > the IOMMU address space") previously resolved this issue for spapr_pci. > We are now seeing this in s390x; it would seem the possibility for this > issue was already present but based on a bisect commit 2d24a6466154 > ("device-core: use RCU for list of children of a bus") has now changed > the timing such that it is now readily reproducible. > > Add logic to ensure listeners are removed before destroying the address > space. > > Reported-by: Niklas Schnelle <schnelle@linux.ibm.com> > Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com> > Reviewed-by: Pierre Morel <pmorel@linux.ibm.com> > Tested-by: Niklas Schnelle <schnelle@linux.ibm.com> > --- > hw/s390x/s390-pci-bus.c | 7 +++++++ > 1 file changed, 7 insertions(+) Thanks, queued to s390-fixes.
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