[Qemu-devel] [PATCH] vfio/pci: do not set the PCIDevice 'has_rom' attribute

[Cédric Le Goater]

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 <address@hidden>
---

 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