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Tsirkin" , Markus Armbruster , qemu-devel@nongnu.org, Greg Kurz , qemu-ppc@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" David Gibson writes: > On Thu, Jul 09, 2020 at 07:12:47PM +0200, Greg Kurz wrote: >> Some recent error handling cleanups unveiled issues with our support of >> PCI bridges: >> >> 1) QEMU aborts when using non-standard PCI bridge types, >> unveiled by commit 7ef1553dac "spapr_pci: Drop some dead error handling" >> >> $ qemu-system-ppc64 -M pseries -device pcie-pci-bridge >> Unexpected error in object_property_find() at qom/object.c:1240: >> qemu-system-ppc64: -device pcie-pci-bridge: Property '.chassis_nr' not found >> Aborted (core dumped) > > Oops, I thought we had a check that we actually had a "pci-bridge" > device before continuing with the hotplug, but I guess not. > >> This happens because we assume all PCI bridge types to have a "chassis_nr" >> property. This property only exists with the standard PCI bridge type >> "pci-bridge" actually. We could possibly revert 7ef1553dac but it seems >> much simpler to check the presence of "chassis_nr" earlier. > > Hrm, right, 7ef1553dac was not really correct since add_drcs() really > can fail. Right. I failed to see that we can run into a bridge without a "chassis_nr" here. >> 2) QEMU abort if same "chassis_nr" value is used several times, >> unveiled by commit d2623129a7de "qom: Drop parameter @errp of >> object_property_add() & friends" >> >> $ qemu-system-ppc64 -M pseries -device pci-bridge,chassis_nr=1 \ >> -device pci-bridge,chassis_nr=1 >> Unexpected error in object_property_try_add() at qom/object.c:1167: >> qemu-system-ppc64: -device pci-bridge,chassis_nr=1: attempt to add duplicate property '40000100' to object (type 'container') >> Aborted (core dumped) Before d2623129a7de, the error got *ignored* in spapr_dr_connector_new(): SpaprDrc *spapr_dr_connector_new(Object *owner, const char *type, uint32_t id) { SpaprDrc *drc = SPAPR_DR_CONNECTOR(object_new(type)); char *prop_name; drc->id = id; drc->owner = owner; prop_name = g_strdup_printf("dr-connector[%"PRIu32"]", spapr_drc_index(drc)); object_property_add_child(owner, prop_name, OBJECT(drc), &error_abort); object_unref(OBJECT(drc)); ---> object_property_set_bool(OBJECT(drc), true, "realized", NULL); g_free(prop_name); return drc; } I doubt that's healthy. >> This happens because we assume that "chassis_nr" values are unique, but >> nobody enforces that and we end up generating duplicate DRC ids. The PCI >> code doesn't really care for duplicate "chassis_nr" properties since it >> is only used to initialize the "Chassis Number Register" of the bridge, >> with no functional impact on QEMU. So, even if passing the same value >> several times might look weird, it never broke anything before, so >> I guess we don't necessarily want to enforce strict checking in the PCI >> code now. > > Yeah, I guess. I'm pretty sure that the chassis number of bridges is > supposed to be system-unique (well, unique within the PCI domain at > least, I guess) as part of the hardware spec. So specifying multiple > chassis ids the same is a user error, but we need a better failure > mode. > >> Workaround both issues in the PAPR code: check that the bridge has a >> unique and non null "chassis_nr" when plugging it into its parent bus. >> >> Fixes: 05929a6c5dfe ("spapr: Don't use bus number for building DRC ids") > > Arguably, it's really fixing 7ef1553dac. I agree 7ef1553dac broke the "use a bridge that doesn't have property 'chassis_nr' case. I suspect the "duplicate chassis_nr" case has always been broken, and d2623129a7de merely uncovered it. If we can trigger the abort with hot-plug, then d2623129a7de made things materially worse (new way to accidentally kill your guest and maybe lose data), and I'd add a Fixes: blaming it. >> Reported-by: Thomas Huth >> Signed-off-by: Greg Kurz > > I had a few misgivings about the details of this, but I think I've > convinced myself they're fine. There's a couple of things I'd like to > polish, but I'll do that as a follow up.