Re: [PATCH v5 2/9] watchdog/hpwdt: Remove legacy NMI sourcing.

[Guenter Roeck <linux@roeck-us.net>]

On 02/28/2018 11:45 AM, Jerry Hoemann wrote:
> On Mon, Feb 26, 2018 at 05:29:55PM -0800, Guenter Roeck wrote:
>> On 02/26/2018 05:02 PM, Jerry Hoemann wrote:
>>> On Mon, Feb 26, 2018 at 06:32:30AM -0800, Guenter Roeck wrote:
>>>> On 02/26/2018 06:11 AM, Arnd Bergmann wrote:
>>>>> On Mon, Feb 26, 2018 at 4:22 AM, Jerry Hoemann <jerry.hoemann@hpe.com> wrote:
>>>>>> Gen8 and prior Proliant systems supported the "CRU" interface
>>>>>> to firmware.  This interfaces allows linux to "call back" into firmware
>>>>>> to source the cause of an NMI.  This feature isn't fully utilized
>>>>>> as the actual source of the NMI isn't printed, the driver only
>>>>>> indicates that the source couldn't be determined when the call
>>>>>> fails.
>>>>>>
>>>>>> With the advent of Gen9, iCRU replaces the CRU. The call back
>>>>>> feature is no longer available in firmware.  To be compatible and
>>>>>> not attempt to call back into firmware on system not supporting CRU,
>>>>>> the SMBIOS table is consulted to determine if it is safe to
>>>>>> make the call back or not.
>>>>>>
>>>>>> This results in about half of the driver code being devoted
>>>>>> to either making CRU calls or determing if it is safe to make
>>>>>> CRU calls.  As noted, the driver isn't really using the results of
>>>>>> the CRU calls.
>>>>>>
>>>>>> Furthermore, as a consequence of the Spectre security issue, the
>>>>>> BIOS/EFI calls are being wrapped into Spectre-disabling section.
>>>>>> Removing the call back in hpwdt_pretimeout assists in this effort.
>>>>>>
>>>>>> As the CRU sourcing of the NMI isn't required for handling the
>>>>>> NMI and there are security concerns with making the call back, remove
>>>>>> the legacy (pre Gen9) NMI sourcing and the DMI code to determine if
>>>>>> the system had the CRU interface.
>>>>>>
>>>>>> Signed-off-by: Jerry Hoemann <jerry.hoemann@hpe.com>
>>>>>
>>>>> This avoids a warning in mainline kernels, so that's great:
>>>>>
>>>>> drivers/watchdog/hpwdt.o: warning: objtool: .text+0x24: indirect call
>>>>> found in RETPOLINE build
>>>>>
>>>>> I wonder what we do about stable kernels. Are both this patch and the patch
>>>>> that added the objtool warning message candidates for backports to
>>>>> stable kernels?
>>>>>
>>>>
>>>> Makes sense to me, but it is really a bit more than a bug fix, so I'll
>>>> leave it up to Jerry/HPE to make the call in respect to hpwdt.
>>>>
>>>
>>> Generally speaking, HPE customers who run linux do so through a distro
>>> vendor and pick up patches from them.  But I'm sure there are some
>>> customers who do things differently.
>>>
>>> The distro vendor's have their own repos and we'll work with them
>>> to back port patches to their code base.  So, I typically don't do a lot
>>> of kernel.org stable branch work.
>>>
>>> Looks like objtool has been enhanced to find Spectre vulnerable code.
>>> Are the other kernel patches related to Spectre being back ported
>>> to stable release lines?  If yes, it probably make sense to do
>>> the hpwdt change as well.
>>>
>>
>> Spectre has been backported to v4.4 and later. I don't know about earlier kernels.
>>
>>> Is just the patch removing the firmware call back wanted/needed? Or the
>>> whole driver rewrite?  (The older baseline don't have all the watchdog
>>> features that the patch set uses.)
>>>
>>
>> We would only want to backport this patch. The rest is really out of scope.
>>
>>> Which stable baseline(s) would need to be patched?  Priority?
>>>
>>> Who does it?  (i.e. do you want me to submit patches to the stable baseline?)
>>>
>> We would tag the patch for stable (and submit it into v4.16-rc). Greg would
>> take care of the rest unless there are conflicts, in which case we get a note
>> telling us that a backport is needed.
>>
> 
> Guenter,
> 
> Are you waiting for anything more from me on this patch, or are we
> good for now until the back ports to v.15 etc.,?
> 

We are good. I'll need to ask Wim to send a pull request to Linus.

Guenter