ACK: [PATCH Wily/Xenial SRU] UBUNTU: SAUCE: powerpc/eeh: Validate arch in eeh_add_device_early()

[Chris J Arges]

On 01/11/2016 11:11 AM, tim.gardner at canonical.com wrote:
> From: "Guilherme G. Piccoli" <gpiccoli at linux.vnet.ibm.com>
> 
> BugLink: http://bugs.launchpad.net/bugs/1486180
> 
> Commit 89a51df5ab1d ("powerpc/eeh: Fix crash in eeh_add_device_early() on Cell")
> added a check on function eeh_add_device_early(): since in Cell arch eeh_ops
> is NULL, that code used to crash on Cell. The commit's approach was validate
> if EEH was available by checking the result of function eeh_enabled().
> 
> Since the function eeh_add_device_early() is used to perform EEH
> initialization in devices added later on the system, like in hotplug/DLPAR
> scenarios, we might reach a case in which no PCI devices are present on boot
> and so EEH is not initialized. Then, if a device is added via DLPAR for
> example, eeh_add_device_early() fails because eeh_enabled() is false.
> 
> We can hit a kernel oops on pSeries arch if eeh_add_device_early() fails:
> if we have no PCI devices on machine at boot time, and then we add a PCI device
> via DLPAR operation, the function query_ddw() triggers the oops on NULL pointer
> dereference in the line "cfg_addr = edev->config_addr;". It happens because
> config_addr in edev is NULL, since the function eeh_add_device_early() was not
> completed successfully.
> 
> This patch just changes the way the arch checking is done in function
> eeh_add_device_early(): we use no more eeh_enabled(), but instead we check the
> running architecture by using the macro machine_is(). If we are running on
> pSeries or PowerNV, the EEH mechanism can be enabled; otherwise, we bail out
> the function. This way, we don't enable EEH on Cell and we don't hit the oops
> on DLPAR either.
> 
> Fixes: 89a51df5ab1d ("powerpc/eeh: Fix crash in eeh_add_device_early() on Cell")
> Signed-off-by: Guilherme G. Piccoli <gpiccoli at linux.vnet.ibm.com>
> Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
> ---
>  arch/powerpc/kernel/eeh.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/eeh.c b/arch/powerpc/kernel/eeh.c
> index 01c961d..3203895 100644
> --- a/arch/powerpc/kernel/eeh.c
> +++ b/arch/powerpc/kernel/eeh.c
> @@ -1071,7 +1071,13 @@ void eeh_add_device_early(struct pci_dn *pdn)
>  	struct pci_controller *phb;
>  	struct eeh_dev *edev = pdn_to_eeh_dev(pdn);
>  
> -	if (!edev || !eeh_enabled())
> +	if (!edev)
> +		return;
> +
> +	/* Some platforms (like Cell) don't have EEH capabilities, so we
> +	 * need to abort here. In case of pseries or powernv, we have EEH
> +	 * so we can continue. */
> +	if (!machine_is(pseries) && !machine_is(powernv))
>  		return;
>  
>  	if (!eeh_has_flag(EEH_PROBE_MODE_DEVTREE))
>