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

[Bjorn Helgaas <bhelgaas@xxxxxxxxxx>]

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?

Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>

> ---
>  arch/ia64/pci/pci.c |   13 ++++++++++---
>  arch/x86/pci/acpi.c |   13 ++++++++++---
>  2 files changed, 20 insertions(+), 6 deletions(-)
> 
> Index: linux-pm/arch/x86/pci/acpi.c
> ===================================================================
> --- linux-pm.orig/arch/x86/pci/acpi.c
> +++ linux-pm/arch/x86/pci/acpi.c
> @@ -482,9 +482,16 @@ struct pci_bus *pci_acpi_scan_root(struc
>  
>  int pcibios_root_bridge_prepare(struct pci_host_bridge *bridge)
>  {
> -     struct pci_sysdata *sd = bridge->bus->sysdata;
> -
> -     ACPI_COMPANION_SET(&bridge->dev, sd->companion);
> +     /*
> +      * We pass NULL as parent to pci_create_root_bus(), so if it is not NULL
> +      * here, pci_create_root_bus() has been called by someone else and
> +      * sysdata is likely to be different from what we expect.  Let it go in
> +      * that case.
> +      */
> +     if (!bridge->dev.parent) {
> +             struct pci_sysdata *sd = bridge->bus->sysdata;
> +             ACPI_COMPANION_SET(&bridge->dev, sd->companion);
> +     }
>       return 0;
>  }
>  
> Index: linux-pm/arch/ia64/pci/pci.c
> ===================================================================
> --- linux-pm.orig/arch/ia64/pci/pci.c
> +++ linux-pm/arch/ia64/pci/pci.c
> @@ -478,9 +478,16 @@ struct pci_bus *pci_acpi_scan_root(struc
>  
>  int pcibios_root_bridge_prepare(struct pci_host_bridge *bridge)
>  {
> -     struct pci_controller *controller = bridge->bus->sysdata;
> -
> -     ACPI_COMPANION_SET(&bridge->dev, controller->companion);
> +     /*
> +      * We pass NULL as parent to pci_create_root_bus(), so if it is not NULL
> +      * here, pci_create_root_bus() has been called by someone else and
> +      * sysdata is likely to be different from what we expect.  Let it go in
> +      * that case.
> +      */
> +     if (!bridge->dev.parent) {
> +             struct pci_controller *controller = bridge->bus->sysdata;
> +             ACPI_COMPANION_SET(&bridge->dev, controller->companion);
> +     }
>       return 0;
>  }
>  
> 

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