powerpc/kdump: Ignore failure in enabling big endian exception during crash

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.

Signed-off-by: Hari Bathini <hbathini@linux.vnet.ibm.com>
[mpe: Rename to kdump_in_progress(), use bool, and edit comment]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

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 bool kdump_in_progress(void)
+{
+	return crashing_cpu >= 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 bool kdump_in_progress(void)
+{
+	return false;
+}
+
 #endif /* CONFIG_KEXEC */
 #endif /* ! __ASSEMBLY__ */
 #endif /* __KERNEL__ */

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 (!kdump_in_progress())
 		kexec_prepare_cpus();
 
 	pr_debug("kexec: Starting switchover sequence.\n");

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"
@@ -267,8 +268,13 @@ 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.
+		 *
+		 * There is a known problem when kdump'ing, if cpus are offline
+		 * the above call will fail. Rather than panicking again, keep
+		 * going and hope the kdump kernel is also little endian, which
+		 * it usually is.
 		 */
-		if (rc)
+		if (rc && !kdump_in_progress())
 			panic("Could not enable big endian exceptions");
 	}
 #endif