powerpc/powernv: Invoke opal_cec_reboot2() on unrecoverable machine check errors.

On non-recoverable MCE errors in kernel space, Linux kernel panics
and system reboots. On BMC based system opal-prd runs as a daemon
in the host. Hence, kernel crash may prevent opal-prd to detect and
analyze this MCE error. This may land us in a situation where the faulty
memory never gets de-configured and Linux would keep hitting same MCE error
again and again. If this happens in early stage of kernel initialization,
then Linux will keep crashing and rebooting in a loop.

This patch fixes this issue by invoking new opal_cec_reboot2() call with
reboot type OPAL_REBOOT_PLATFORM_ERROR to inform BMC/OCC about this
error, so that BMC can collect relevant data for error analysis and
decide what component to de-configure before rebooting.

This patch is dependent on OPAL patchset posted on skiboot mailing list
at https://lists.ozlabs.org/pipermail/skiboot/2015-July/001771.html that
introduces opal_cec_reboot2() opal call.
Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/opal-api.h

@@ -154,7 +154,8 @@
 #define OPAL_FLASH_WRITE			111
 #define OPAL_FLASH_ERASE			112
 #define OPAL_PRD_MSG				113
-#define OPAL_LAST				113
+#define OPAL_CEC_REBOOT2			116
+#define OPAL_LAST				116
 
 /* Device tree flags */
 
@@ -857,6 +858,12 @@ enum OpalSysCooling {
 	OPAL_SYSCOOL_INSF	= 0x0001, /* System insufficient cooling */
 };
 
+/* Argument to OPAL_CEC_REBOOT2() */
+enum {
+	OPAL_REBOOT_NORMAL		= 0,
+	OPAL_REBOOT_PLATFORM_ERROR	= 1,
+};
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __OPAL_API_H */

arch/powerpc/include/asm/opal.h

@@ -44,6 +44,7 @@ int64_t opal_tpo_write(uint64_t token, uint32_t year_mon_day,
 		       uint32_t hour_min);
 int64_t opal_cec_power_down(uint64_t request);
 int64_t opal_cec_reboot(void);
+int64_t opal_cec_reboot2(uint32_t reboot_type, char *diag);
 int64_t opal_read_nvram(uint64_t buffer, uint64_t size, uint64_t offset);
 int64_t opal_write_nvram(uint64_t buffer, uint64_t size, uint64_t offset);
 int64_t opal_handle_interrupt(uint64_t isn, __be64 *outstanding_event_mask);

arch/powerpc/platforms/powernv/opal-wrappers.S

@@ -202,6 +202,7 @@ OPAL_CALL(opal_rtc_read,			OPAL_RTC_READ);
 OPAL_CALL(opal_rtc_write,			OPAL_RTC_WRITE);
 OPAL_CALL(opal_cec_power_down,			OPAL_CEC_POWER_DOWN);
 OPAL_CALL(opal_cec_reboot,			OPAL_CEC_REBOOT);
+OPAL_CALL(opal_cec_reboot2,			OPAL_CEC_REBOOT2);
 OPAL_CALL(opal_read_nvram,			OPAL_READ_NVRAM);
 OPAL_CALL(opal_write_nvram,			OPAL_WRITE_NVRAM);
 OPAL_CALL(opal_handle_interrupt,		OPAL_HANDLE_INTERRUPT);

arch/powerpc/platforms/powernv/opal.c

@@ -441,6 +441,7 @@ static int opal_recover_mce(struct pt_regs *regs,
 int opal_machine_check(struct pt_regs *regs)
 {
 	struct machine_check_event evt;
+	int ret;
 
 	if (!get_mce_event(&evt, MCE_EVENT_RELEASE))
 		return 0;
@@ -455,6 +456,40 @@ int opal_machine_check(struct pt_regs *regs)
 
 	if (opal_recover_mce(regs, &evt))
 		return 1;
+
+	/*
+	 * Unrecovered machine check, we are heading to panic path.
+	 *
+	 * We may have hit this MCE in very early stage of kernel
+	 * initialization even before opal-prd has started running. If
+	 * this is the case then this MCE error may go un-noticed or
+	 * un-analyzed if we go down panic path. We need to inform
+	 * BMC/OCC about this error so that they can collect relevant
+	 * data for error analysis before rebooting.
+	 * Use opal_cec_reboot2(OPAL_REBOOT_PLATFORM_ERROR) to do so.
+	 * This function may not return on BMC based system.
+	 */
+	ret = opal_cec_reboot2(OPAL_REBOOT_PLATFORM_ERROR,
+			"Unrecoverable Machine Check exception");
+	if (ret == OPAL_UNSUPPORTED) {
+		pr_emerg("Reboot type %d not supported\n",
+					OPAL_REBOOT_PLATFORM_ERROR);
+	}
+
+	/*
+	 * We reached here. There can be three possibilities:
+	 * 1. We are running on a firmware level that do not support
+	 *    opal_cec_reboot2()
+	 * 2. We are running on a firmware level that do not support
+	 *    OPAL_REBOOT_PLATFORM_ERROR reboot type.
+	 * 3. We are running on FSP based system that does not need opal
+	 *    to trigger checkstop explicitly for error analysis. The FSP
+	 *    PRD component would have already got notified about this
+	 *    error through other channels.
+	 *
+	 * In any case, let us just fall through. We anyway heading
+	 * down to panic path.
+	 */
 	return 0;
 }