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

[Jerry Hoemann]

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@xxxxxxx> 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@xxxxxxx>
> > 
> > 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.

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.)

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?)

Thanks

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Jerry Hoemann                  Software Engineer   Hewlett Packard Enterprise
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