Re: [PATCH 3/3] PCI/AER: Covertly inject errors with ftrace hooks

[Keith Busch <keith.busch@intel.com>]

On Thu, Oct 11, 2018 at 12:08:26PM -0500, Bjorn Helgaas wrote:
> On Thu, Oct 11, 2018 at 10:52:07AM -0600, Keith Busch wrote:
> > The aer_inject module had been intercepting config requests by overwriting
> > the config accessor operations in the pci_bus ops.  This has several
> > issues.
> > 
> > First, the module was tracking kernel objects unbeknownst to the drivers
> > that own them.  The kernel may free those devices, leaving the AER inject
> > module holding stale references and no way to know that happened.
> > 
> > Second, the PCI enumeration has child devices inherit pci_bus ops from
> > the parent bus.  Since errors may lead to link resets that trigger
> > re-enumeration, the child devices would inherit operations that don't
> > know about the devices using them, causing kernel crashes.
> > 
> > Finally, CONFIG_PCI_LOCKLESS_CONFIG doesn't block accessing the pci_bus
> > ops, so it's racing with potential in-flight config requests.
> > 
> > This patch uses a different error injection approach leveraging ftrace
> > to thunk the config space functions.  If the kernel and architecture
> > are capable, the ftrace hook will overwrite the processor's function
> > call address with the address of the error injecting function. This way
> > doesn't modify or track driver structures, fixing the issues with the
> > current method.
> > 
> > If either the kernel config or platform arch do not support the necessary
> > ftrace capabilities, the aer_inject module will fallback to the older
> > way so that it may continue to be used as before.
> > 
> > Signed-off-by: Keith Busch <keith.busch@intel.com>
> > ---
> >  drivers/pci/pcie/aer_inject.c | 218 ++++++++++++++++++++++++++++++++++++------
> >  1 file changed, 189 insertions(+), 29 deletions(-)
> > 
> > diff --git a/drivers/pci/pcie/aer_inject.c b/drivers/pci/pcie/aer_inject.c
> > index 726987f8d53c..4825fa465b60 100644
> > --- a/drivers/pci/pcie/aer_inject.c
> > +++ b/drivers/pci/pcie/aer_inject.c
> 
> > +static int aer_inj_legacy_read(struct pci_bus *bus, unsigned int devfn,
> > +			       int where, int size, u32 *val)
> > +{
> > +	struct pci_ops *ops, *my_ops;
> > +	int rv;
> > +
> > +	ops = __find_pci_bus_ops(bus);
> > +	if (!ops)
> > +		return -1;
> > +
> > +	my_ops = bus->ops;
> > +	bus->ops = ops;
> > +	rv = ops->read(bus, devfn, where, size, val);
> > +	bus->ops = my_ops;
> > +
> > +	return rv;
> > +}
> > +
> > +static int aer_inj_legacy_write(struct pci_bus *bus, unsigned int devfn,
> > +				int where, int size, u32 val)
> > +{
> > +	struct pci_ops *ops, *my_ops;
> > +	int rv;
> > +
> > +	ops = __find_pci_bus_ops(bus);
> > +	if (!ops)
> > +		return -1;
> > +
> > +	my_ops = bus->ops;
> > +	bus->ops = ops;
> > +	rv = ops->write(bus, devfn, where, size, val);
> > +	bus->ops = my_ops;
> > +
> > +	return rv;
> > +}
> 
> Is there any chance you could split this into two (or more) patches?
> 
> The part above looks like pretty straightforward code movement without
> any functional change.  It would be nice to get that part out of the way,
> then have a smaller patch that adds the fancy ftrace stuff.

No problem, will do.