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Re: [Qemu-devel] [PATCH] vfio/pci: do not set the PCIDevice 'has_rom' at
From: |
Alex Williamson |
Subject: |
Re: [Qemu-devel] [PATCH] vfio/pci: do not set the PCIDevice 'has_rom' attribute |
Date: |
Mon, 9 Jul 2018 08:30:38 -0600 |
On Mon, 9 Jul 2018 09:04:47 +0200
Cédric Le Goater <address@hidden> wrote:
> On 07/06/2018 07:16 PM, Alex Williamson wrote:
> > On Fri, 6 Jul 2018 18:36:14 +0200
> > Cédric Le Goater <address@hidden> 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 <address@hidden>
> >
> > I think the segfault can be attributed to:
> >
> > fa53a0e53efd ("memory: drop find_ram_block()")
> >
> > Prior to that vmstate_unregister_ram() called
> > memory_region_get_ram_addr() which would have resulted in
> > RAM_ADDR_INVALID. This would have been passed to
> > qemu_ram_unset_idstr() which would have used find_ram_block() to lookup
> > the RAMBlock, which would be NULL for the invalid address, safely
> > avoiding any sort of segfault.
>
> Yes, but since, commit b895de502717 ("migration: discard non-migratable
> RAMBlocks") added :
>
> void vmstate_unregister_ram(MemoryRegion *mr, DeviceState *dev)
> {
> qemu_ram_unset_idstr(mr->ram_block);
> + qemu_ram_unset_migratable(mr->ram_block);
> }
>
> and qemu_ram_unset_migratable() does not check the block validity.
Ok, yes I see that qemu_ram_unset_idstr() does avoid the NULL pointer
dereference, so I'll make the fixes tag reference to b895de502717.
Thanks,
Alex
> >> ---
> >>
> >> 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;
> >> }
> >>
> >
>