pseries: Add H_SET_MODE to change exception endianness

On little endian builds call H_SET_MODE so exceptions have the
correct endianness. We need to reset the endian during kexec
so do that in the MMU hashtable clear callback.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

4 files changed, 87 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/hvcall.h b/arch/powerpc/include/asm/hvcall.h
index 0c7f2bfcf134..d8b600b3f058 100644
--- a/arch/powerpc/include/asm/hvcall.h
+++ b/arch/powerpc/include/asm/hvcall.h
@@ -403,6 +403,8 @@ static inline unsigned long cmo_get_page_size(void)
 extern long pSeries_enable_reloc_on_exc(void);
 extern long pSeries_disable_reloc_on_exc(void);
 
+extern long pseries_big_endian_exceptions(void);
+
 #else
 
 #define pSeries_enable_reloc_on_exc()  do {} while (0)
diff --git a/arch/powerpc/include/asm/plpar_wrappers.h b/arch/powerpc/include/asm/plpar_wrappers.h
index a63b045e707c..12c32c5f533d 100644
--- a/arch/powerpc/include/asm/plpar_wrappers.h
+++ b/arch/powerpc/include/asm/plpar_wrappers.h
@@ -287,6 +287,32 @@ static inline long disable_reloc_on_exceptions(void) {
         return plpar_set_mode(0, 3, 0, 0);
 }
 
+/*
+ * Take exceptions in big endian mode on this partition
+ *
+ * Note: this call has a partition wide scope and can take a while to complete.
+ * If it returns H_LONG_BUSY_* it should be retried periodically until it
+ * returns H_SUCCESS.
+ */
+static inline long enable_big_endian_exceptions(void)
+{
+        /* mflags = 0: big endian exceptions */
+        return plpar_set_mode(0, 4, 0, 0);
+}
+
+/*
+ * Take exceptions in little endian mode on this partition
+ *
+ * Note: this call has a partition wide scope and can take a while to complete.
+ * If it returns H_LONG_BUSY_* it should be retried periodically until it
+ * returns H_SUCCESS.
+ */
+static inline long enable_little_endian_exceptions(void)
+{
+        /* mflags = 1: little endian exceptions */
+        return plpar_set_mode(1, 4, 0, 0);
+}
+
 static inline long plapr_set_ciabr(unsigned long ciabr)
 {
         return plpar_set_mode(0, 1, ciabr, 0);
diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index 356bc75ca74f..4fca3def9db9 100644
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -245,6 +245,23 @@ static void pSeries_lpar_hptab_clear(void)
                                         &(ptes[j].pteh), &(ptes[j].ptel));
                 }
         }
+
+#ifdef __LITTLE_ENDIAN__
+        /* Reset exceptions to big endian */
+        if (firmware_has_feature(FW_FEATURE_SET_MODE)) {
+                long rc;
+
+                rc = pseries_big_endian_exceptions();
+                /*
+                 * At this point it is unlikely panic() will get anything
+                 * out to the user, but at least this will stop us from
+                 * continuing on further and creating an even more
+                 * difficult to debug situation.
+                 */
+                if (rc)
+                        panic("Could not enable big endian exceptions");
+        }
+#endif
 }
 
 /*
diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
index 1f97e2b87a62..c1f190858701 100644
--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -442,6 +442,32 @@ static void pSeries_machine_kexec(struct kimage *image)
 }
 #endif
 
+#ifdef __LITTLE_ENDIAN__
+long pseries_big_endian_exceptions(void)
+{
+        long rc;
+
+        while (1) {
+                rc = enable_big_endian_exceptions();
+                if (!H_IS_LONG_BUSY(rc))
+                        return rc;
+                mdelay(get_longbusy_msecs(rc));
+        }
+}
+
+static long pseries_little_endian_exceptions(void)
+{
+        long rc;
+
+        while (1) {
+                rc = enable_little_endian_exceptions();
+                if (!H_IS_LONG_BUSY(rc))
+                        return rc;
+                mdelay(get_longbusy_msecs(rc));
+        }
+}
+#endif
+
 static void __init pSeries_setup_arch(void)
 {
         panic_timeout = 10;
@@ -698,6 +724,22 @@ static int __init pSeries_probe(void)
         /* Now try to figure out if we are running on LPAR */
         of_scan_flat_dt(pseries_probe_fw_features, NULL);
 
+#ifdef __LITTLE_ENDIAN__
+        if (firmware_has_feature(FW_FEATURE_SET_MODE)) {
+                long rc;
+                /*
+                 * Tell the hypervisor that we want our exceptions to
+                 * be taken in little endian mode. If this fails we don't
+                 * want to use BUG() because it will trigger an exception.
+                 */
+                rc = pseries_little_endian_exceptions();
+                if (rc) {
+                        ppc_md.progress("H_SET_MODE LE exception fail", 0);
+                        panic("Could not enable little endian exceptions");
+                }
+        }
+#endif
+
         if (firmware_has_feature(FW_FEATURE_LPAR))
                 hpte_init_lpar();
         else