Re: [Xen-devel] [PATCH] PCI / ACPI: Do not set ACPI companions for host bridges with parents

["Rafael J. Wysocki" <rafael@xxxxxxxxxx>]

On Thu, May 28, 2015 at 12:58 AM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote:
> On Tue, May 26, 2015 at 04:17:05AM +0200, Rafael J. Wysocki wrote:
>> On Tuesday, May 26, 2015 03:08:17 AM Rafael J. Wysocki wrote:
>> > On Tuesday, May 26, 2015 01:42:16 AM Rafael J. Wysocki wrote:
>> > > On Tuesday, May 26, 2015 01:22:12 AM Rafael J. Wysocki wrote:
>> > > > On Friday, May 22, 2015 09:53:37 PM Boris Ostrovsky wrote:
>> > > > > On 05/22/2015 04:11 AM, Sander Eikelenboom wrote:
>> > > > > > Hello Sander,
>> > > > > >
>> > >
>> > > [cut]
>> > >
>> > > > > (+Rafael again)
>> > > > >
>> > > > > So the immediate cause of those errors is that pdev->evtchn is 0.
>> > > > > Backend is not notified and things not go well then.
>> > > > >
>> > > > > And it is indeed caused by 97badf873ab60e841243b66133ff9eff2a46ef29:
>> > > > >
>> > > > > We allocate pcifront_sd in pcifront_scan_root() and then pass it to
>> > > > > pci_scan_bus_parented() as sysdata. Eventually this sysdata is used 
>> > > > > in
>> > > > > pcibios_root_bridge_prepare() as pci_sysdata. It is dereferenced as
>> > > > > pci_sysdata->companion (which I believe is aliased to 
>> > > > > pcifront_sd->pdev)
>> > >
>> > > Well, there is an int node field between them, so I'm not sure.
>> > >
>> > > > > and then set_primary_fwnode() writes it, thus corrupting
>> > > > > pcifront_sd->pdev (and I think this is what sets evtchn to zero).
>> > >
>> > > So the corruption happens when set_primary_fwnode() writes NULL to the
>> > > 'secondary' field of object pointed to by 'fwnode'.
>> > >
>> > > This isn't strictly necessary and we might avoid the crash by only
>> > > writing to fwnode->secondary if fn is not NULL.
>> > >
>> > > So, Sander please test the patch below too if possible.
>> > >
>> > > Of course, that doesn't solve a problem of passing an incorrect pointer
>> > > to ACPI_COMPANION_SET() in pcibios_root_bridge_prepare().
>> >
>> > And here's one more thing to test.
>>
>> And the below is how I'd fix it, so you can simply test this patch and skip 
>> the
>> previous ones.
>>
>> ---
>> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>> Subject: PCI / ACPI: Do not set ACPI companions for host bridges with parents
>>
>> Commit 97badf873ab6 (device property: Make it possible to use
>> secondary firmware nodes) uncovered a bug in the x86 (and ia64) PCI
>> host bridge initialization code that assumes bridge->bus->sysdata
>> to always point to a struct pci_sysdata object which need not be
>> the case (in particular, the Xen PCI frontend driver sets it to point
>> to a different data type).  If it is not the case, an incorrect
>> pointer (or a piece of data that is not a pointer at all) will be
>> passed to ACPI_COMPANION_SET() and that may cause interesting
>> breakage to happen going forward.
>>
>> To work around this problem use the observation that the ACPI
>> host bridge initialization always passes NULL as parent to
>> pci_create_root_bus(), so if pcibios_root_bridge_prepare() sees
>> a non-NULL parent of the bridge, it should not attempt to set
>> an ACPI companion for it, because that means that
>> pci_create_root_bus() has been called by someone else.
>>
>> Reported-by: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>
> Do you want to merge this, Rafael?

I can do that.

> Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>

Thanks!

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