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SubjectRe: [Xen-devel] Regression due to "device property: Make it possible to use secondary firmware nodes" Re: Xen-unstable + linux 4.1-mergewindow: problems with PV guest pci passthrough: pcifront pci-0: pciback not responding!!!
Date
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().

---
drivers/base/core.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

Index: linux-pm/drivers/base/core.c
===================================================================
--- linux-pm.orig/drivers/base/core.c
+++ linux-pm/drivers/base/core.c
@@ -2167,7 +2167,9 @@ void set_primary_fwnode(struct device *d
if (fwnode_is_primary(fn))
fn = fn->secondary;

- fwnode->secondary = fn;
+ if (fn)
+ fwnode->secondary = fn;
+
dev->fwnode = fwnode;
} else {
dev->fwnode = fwnode_is_primary(dev->fwnode) ?


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