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

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