powerpc/powernv: Flush console before platform error reboot

Unrecovered MCE and HMI errors are sent through a special restart OPAL
call to log the platform error. The downside is that they don't go
through normal Linux crash paths, so they don't give much information
to the Linux console.

Change this by providing a special crash function which does some of
the console flushing from the panic() path before calling firmware to
reboot.

The downside of this is a little more code to execute before reaching
the firmware reboot. However in practice, it's critical to get the
Linux console messages output in order to debug a problem. So this is
a desirable tradeoff.

Note on the implementation: It is difficult to plumb a custom reboot
handler into the panic path, because panic does a little bit too much
work. For example, it will try to delay with the timebase, but that
may be corrupted in some cases resulting in a hang without reaching
the platform reboot. Another problem is that panic can invoke the
crash dump code which is not what we want in the case of a hardware
platform error. Long-term the best solution will be to rework the
panic path so it can be suitable for this kind of panic, but for now
we just duplicate a bit of the code.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 51 insertions, 38 deletions

diff --git a/arch/powerpc/platforms/powernv/opal.c b/arch/powerpc/platforms/powernv/opal.c
index 4448e458a797..d246f919cba2 100644
--- a/arch/powerpc/platforms/powernv/opal.c
+++ b/arch/powerpc/platforms/powernv/opal.c
@@ -26,6 +26,10 @@
 #include <linux/memblock.h>
 #include <linux/kthread.h>
 #include <linux/freezer.h>
+#include <linux/printk.h>
+#include <linux/kmsg_dump.h>
+#include <linux/console.h>
+#include <linux/sched/debug.h>
 
 #include <asm/machdep.h>
 #include <asm/opal.h>
@@ -435,10 +439,55 @@ static int opal_recover_mce(struct pt_regs *regs,
 	return recovered;
 }
 
+void pnv_platform_error_reboot(struct pt_regs *regs, const char *msg)
+{
+	/*
+	 * This is mostly taken from kernel/panic.c, but tries to do
+	 * relatively minimal work. Don't use delay functions (TB may
+	 * be broken), don't crash dump (need to set a firmware log),
+	 * don't run notifiers. We do want to get some information to
+	 * Linux console.
+	 */
+	console_verbose();
+	bust_spinlocks(1);
+	pr_emerg("Hardware platform error: %s\n", msg);
+	if (regs)
+		show_regs(regs);
+	smp_send_stop();
+	printk_safe_flush_on_panic();
+	kmsg_dump(KMSG_DUMP_PANIC);
+	bust_spinlocks(0);
+	debug_locks_off();
+	console_flush_on_panic();
+
+	/*
+	 * Don't bother to shut things down because this will
+	 * xstop the system.
+	 */
+	if (opal_cec_reboot2(OPAL_REBOOT_PLATFORM_ERROR, msg)
+						== OPAL_UNSUPPORTED) {
+		pr_emerg("Reboot type %d not supported for %s\n",
+				OPAL_REBOOT_PLATFORM_ERROR, msg);
+	}
+
+	/*
+	 * 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.
+	 */
+
+	ppc_md.restart(NULL);
+}
+
 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;
@@ -454,43 +503,7 @@ 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.
-	 *
-	 * If hardware marked this as an unrecoverable MCE, we are
-	 * going to panic anyway. Even if it didn't, it's not safe to
-	 * continue at this point, so we should explicitly panic.
-	 */
-
-	panic("PowerNV Unrecovered Machine Check");
-	return 0;
+	pnv_platform_error_reboot(regs, "Unrecoverable Machine Check exception");
 }
 
 /* Early hmi handler called in real mode. */