On Fri, Jul 06, 2018 at 06:36:14PM +0200, Cédric Le Goater wrote:
> PCI devices needing a ROM allocate an optional MemoryRegion with
> pci_add_option_rom(). pci_del_option_rom() does the cleanup when the
> device is destroyed. The only action taken by this routine is to call
> vmstate_unregister_ram() which clears the id string of the optional
> ROM RAMBlock and now, also flags the RAMBlock as non-migratable. This
> was recently added by commit b895de502717 ("migration: discard
> non-migratable RAMBlocks"), .
>
> VFIO devices do their own loading of the PCI option ROM in
> vfio_pci_size_rom(). The memory region is switched to an I/O region
> and the PCI attribute 'has_rom' is set but the RAMBlock of the ROM
> region is not allocated. When the associated PCI device is deleted,
> pci_del_option_rom() calls vmstate_unregister_ram() which tries to
> flag a NULL RAMBlock, leading to a SEGV.
>
> It seems that 'has_rom' was set to have memory_region_destroy()
> called, but since commit 469b046ead06 ("memory: remove
> memory_region_destroy") this is not necessary anymore as the
> MemoryRegion is freed automagically.
>
> Remove the PCIDevice 'has_rom' attribute setting in vfio.
>
> Signed-off-by: Cédric Le Goater <c...@kaod.org>
Reviewed-by: Michael S. Tsirkin <m...@redhat.com>
> ---
>
> Tested on a KVM POWER9 pseries machine and a Mellanox MT27710
> Ethernet controller. Performed a couple of plug/unplug, migrated, and
> did a couple more unplug/plug before powering off.
>
> The same tests were done with the previous patches which were
> addressing the issue at a different level :
>
> 1. [PATCH] exec.c: check RAMBlock validity before changing its flag
> https://lists.gnu.org/archive/html/qemu-devel/2018-07/msg00009.html
>
> 2. [PATCH] pci: remove pci_del_option_rom()
> https://lists.gnu.org/archive/html/qemu-devel/2018-07/msg01651.html
>
> Do we still want to remove pci_del_option_rom() ?
>
> 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>)
>
> hw/vfio/pci.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index a1577dea7fdb..6cbb8fa0549d 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -990,7 +990,6 @@ static void vfio_pci_size_rom(VFIOPCIDevice *vdev)
> pci_register_bar(&vdev->pdev, PCI_ROM_SLOT,
> PCI_BASE_ADDRESS_SPACE_MEMORY, &vdev->pdev.rom);
>
> - vdev->pdev.has_rom = true;
> vdev->rom_read_failed = false;
> }
>
> --
> 2.17.1
