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To: Arnd Bergmann , Jerry Hoemann Cc: Wim Van Sebroeck , linux-watchdog@vger.kernel.org, Linux Kernel Mailing List , rwright@hpe.com, maurice.a.saldivar@hpe.com, Ingo Molnar , marcus.folkesson@gmail.com, Josh Poimboeuf , stable References: <20180226032227.14615-1-jerry.hoemann@hpe.com> <20180226032227.14615-3-jerry.hoemann@hpe.com> From: Guenter Roeck Message-ID: <03b13d44-9ce3-ead8-020d-4b1b8114079d@roeck-us.net> Date: Mon, 26 Feb 2018 06:32:30 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On 02/26/2018 06:11 AM, Arnd Bergmann wrote: > On Mon, Feb 26, 2018 at 4:22 AM, Jerry Hoemann 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 > > 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