On 07/02/2018 05:57 AM, Peter Xu wrote: > On Sun, Jul 01, 2018 at 07:19:53PM +0200, Cédric Le Goater wrote: >> When a PCI device is unplugged, the PCI memory regions are deleted >> before the optional ROM RAMBlock is flagged non-migratable. But, when >> this is done, the RAMBlock has already been cleared from the region, >> leading to a segv. >> >> Fix the issue by testing the RAMBlock before flagging it, as it is >> done in qemu_ram_unset_idstr() >> >> Signed-off-by: Cédric Le Goater <c...@kaod.org> >> --- >> >> I caught this bug while deleting a passthrough device from a pseries >> machine. Here is the stack: >> >> #0 qemu_ram_unset_migratable (rb=0x0) at >> /home/legoater/work/qemu/qemu-xive-3.0.git/exec.c:1994 >> #1 0x000000010072def0 in vmstate_unregister_ram (mr=0x101796af0, >> dev=<optimized out>) >> #2 0x0000000100694e5c in pci_del_option_rom (pdev=0x101796330) >> #3 pci_qdev_unrealize (dev=<optimized out>, errp=<optimized out>) >> #4 0x00000001005ff910 in device_set_realized (obj=0x101796330, >> value=<optimized out>, errp=0x0) >> #5 0x00000001007a487c in property_set_bool (obj=0x101796330, >> v=<optimized out>, name=<optimized out>, >> #6 0x00000001007a7878 in object_property_set (obj=0x101796330, >> v=0x7fff70033110, >> #7 0x00000001007aaf1c in object_property_set_qobject (obj=0x101796330, >> value=<optimized out>, >> #8 0x00000001007a7b90 in object_property_set_bool (obj=0x101796330, >> value=<optimized out>, >> #9 0x00000001005fcdd8 in device_unparent (obj=0x101796330) >> #10 0x00000001007a6dd0 in object_finalize_child_property (obj=<optimized >> out>, name=<optimized out>, >> #11 0x00000001007a50c0 in object_property_del_child (obj=0x10111f800, >> child=0x101796330, >> #12 0x0000000100425cc0 in spapr_phb_remove_pci_device_cb (dev=0x101796330) >> #13 0x0000000100427974 in spapr_drc_release (drc=0x1017e2df0) >> #14 0x0000000100429098 in spapr_drc_detach (drc=0x1017e2df0) >> #15 0x00000001004294e0 in drc_isolate_physical (drc=0x1017e2df0) >> #16 0x000000010042a50c in rtas_set_isolation_state (state=0, >> idx=<optimized out>) >> >> May be we should call pci_del_option_rom() before >> pci_unregister_io_regions() ? > > This seems to make more sense to me. > > Meanwhile I assume the name pci_del_option_rom() is a bit misleading - > it's not really deleting the ROM but unregistering the ROM only. > Instead IIUC it's pci_unregister_io_regions() which deleted that. So > maybe we can either rename the function pci_del_option_rom(), or we > can pick the ROM destruction out of pci_unregister_io_regions() and > put it into pci_del_option_rom() to make sure it's done as the last > step?
So it is a little more complex than I thought. The PCI device is a vfio PCI device and the PCI ROM region is initialized in vfio_pci_size_rom() with memory_region_init_io(), which does not allocate the RAMBlock, but has_rom is still set to true. When the device is deleted, pci_del_option_rom() is called and with it, vmstate_unregister_ram() because has_rom is set to true. Leading to the SEGV. I am not sure how to handle this case. It seems that the realize routine of VFIOPCIDevice is hijacking a little the PCIDevice layer. C.