[PATCH v3] PCI: Fix crash during pci_dev hot-unplug on pseries KVM guest

[Michael Ellerman]

Amit Machhiwal <amachhiw at linux.ibm.com> writes:
> On 2024/08/15 01:20 PM, Michael Ellerman wrote:
>> Bjorn Helgaas <helgaas at kernel.org> writes:
>> > On Sat, Aug 03, 2024 at 12:03:25AM +0530, Amit Machhiwal wrote:
>> >> With CONFIG_PCI_DYNAMIC_OF_NODES [1], a hot-plug and hot-unplug sequence
>> >> of a PCI device attached to a PCI-bridge causes following kernel Oops on
>> >> a pseries KVM guest:
>> >
>> > What is unique about pseries here?  There's nothing specific to
>> > pseries in the patch, so I would expect this to be a generic problem
>> > on any arch.
>> >
>> >>  RTAS: event: 2, Type: Hotplug Event (229), Severity: 1
>> >>  Kernel attempted to read user page (10ec00000048) - exploit attempt? (uid: 0)
>> >>  BUG: Unable to handle kernel data access on read at 0x10ec00000048
>> >
>> > Weird address.  I would expect NULL or something.  Where did this
>> > non-NULL pointer come from?
>> 
>> It originally comes from np->data, which is supposed to be an
>> of_changeset.
>> 
>> The powerpc code also uses np->data for the struct pci_dn pointer, see
>> pci_add_device_node_info().
>> 
>> I wonder if that's why it's non-NULL?
>
> I'm also looking into the code to figure out where's that value coming from. I
> will update as soon as I get there.

Thanks.
 
>> Amit, do we have exact steps to reproduce this? I poked around a bit but
>> couldn't get it to trigger.
>
> Sure, below are the steps:
>
> 1. Set CONFIG_PCI_DYNAMIC_OF_NODES=y in the kernel config and compile (Fedora
>    has it disabled in it's distro config, Ubuntu has it enabled but will have it
>    disabled in the next update)
>
> 2. If you are using Fedora cloud images, make sure you've these packages
>    installed:
>     $ rpm -qa | grep -e 'ppc64-diag\|powerpc-utils'
>     powerpc-utils-core-1.3.11-6.fc40.ppc64le
>     powerpc-utils-1.3.11-6.fc40.ppc64le
>     ppc64-diag-rtas-2.7.9-6.fc40.ppc64le
>     ppc64-diag-2.7.9-6.fc40.ppc64le
>
> 3. Hotplug a pci device as follows:
>     virsh attach-interface <domain_name> bridge --source virbr0

I don't use virsh :)

Any idea how to do it with just qemu monitor commands?

cheers