Subject: [PATCH v2] powerpc/kdump: Ignore failure in enabling big endian exception during crash

From: Hari Bathini <[email-masked]>
Date: Thu, 18 Dec 2014 23:36:55 +0530

In LE kernel, we currently have a hack for kexec that resets the exception
endian before starting a new kernel as the kernel that is loaded could be a
big endian or a little endian kernel. In kdump case, resetting exception
endian fails when one or more cpus is disabled. But we can ignore the failure
and still go ahead, as in most cases crashkernel will be of same endianess
as primary kernel and reseting endianess is not even needed in those cases.
This patch adds a new inline function to say if this is kdump path. This
function is used at places where such a check is needed.

Changes from v1:
Instead of skipping, ignore failure in enabling big endian exception
during crash

Signed-off-by: Hari Bathini <[email-masked]>
---
 arch/powerpc/include/asm/kexec.h       |   10 ++++++++++
 arch/powerpc/kernel/machine_kexec_64.c |    2 +-
 arch/powerpc/platforms/pseries/lpar.c  |   10 +++++++++-
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/kexec.h b/arch/powerpc/include/asm/kexec.h
index 19c36cb..0d96d4d 100644
--- a/arch/powerpc/include/asm/kexec.h
+++ b/arch/powerpc/include/asm/kexec.h
@@ -86,6 +86,11 @@ extern int overlaps_crashkernel(unsigned long start, unsigned long size);
 extern void reserve_crashkernel(void);
 extern void machine_kexec_mask_interrupts(void);
 
+static inline int is_kdump_path(void)
+{
+	return (crashing_cpu >= 0) ? 1 : 0;
+}
+
 #else /* !CONFIG_KEXEC */
 static inline void crash_kexec_secondary(struct pt_regs *regs) { }
 
@@ -106,6 +111,11 @@ static inline int crash_shutdown_unregister(crash_shutdown_t handler)
 	return 0;
 }
 
+static inline int is_kdump_path(void)
+{
+	return 0;
+}
+
 #endif /* CONFIG_KEXEC */
 #endif /* ! __ASSEMBLY__ */
 #endif /* __KERNEL__ */
diff --git a/arch/powerpc/kernel/machine_kexec_64.c b/arch/powerpc/kernel/machine_kexec_64.c
index 879b3aa..b4fe804 100644
--- a/arch/powerpc/kernel/machine_kexec_64.c
+++ b/arch/powerpc/kernel/machine_kexec_64.c
@@ -330,7 +330,7 @@ void default_machine_kexec(struct kimage *image)
         * using debugger IPI.
         */
 
-	if (crashing_cpu == -1)
+	if (!is_kdump_path())
 		kexec_prepare_cpus();
 
 	pr_debug("kexec: Starting switchover sequence.\n");
diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index 469751d..63214fa 100644
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -43,6 +43,7 @@
 #include <asm/trace.h>
 #include <asm/firmware.h>
 #include <asm/plpar_wrappers.h>
+#include <asm/kexec.h>
 #include <asm/fadump.h>
 
 #include "pseries.h"
@@ -257,6 +258,7 @@ static void pSeries_lpar_hptab_clear(void)
 	 *
 	 * This is also called on boot when a fadump happens. In that case we
 	 * must not change the exception endian mode.
+	 *
 	 */
 	if (firmware_has_feature(FW_FEATURE_SET_MODE) && !is_fadump_active()) {
 		long rc;
@@ -267,8 +269,14 @@ static void pSeries_lpar_hptab_clear(void)
 		 * out to the user, but at least this will stop us from
 		 * continuing on further and creating an even more
 		 * difficult to debug situation.
+		 *
+		 * But if we reaching here after a crash, no point panicking.
+		 * Also, in kdump path, resetting endianess may not be needed
+		 * as the crashkernel most of the times is of same endianess
+		 * as primary kernel. So, let's ignore the failure and try
+		 * kdump'ing anyway.
 		 */
-		if (rc)
+		if (rc && !is_kdump_path())
 			panic("Could not enable big endian exceptions");
 	}
 #endif