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

[Guenter Roeck]

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.

Guenter