2 files changed, 15 insertions, 4 deletions

diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S
index 316465a32a9c..5c43063d2506 100644
--- a/arch/powerpc/kernel/exceptions-64e.S
+++ b/arch/powerpc/kernel/exceptions-64e.S
@@ -191,6 +191,12 @@ exc_##n##_bad_stack:							    \
         sth     r1,PACA_TRAP_SAVE(r13); /* store trap */                    \
         b       bad_stack_book3e;       /* bad stack error */
 
+/* WARNING: If you change the layout of this stub, make sure you chcek
+        *   the debug exception handler which handles single stepping
+        *   into exceptions from userspace, and the MM code in
+        *   arch/powerpc/mm/tlb_nohash.c which patches the branch here
+        *   and would need to be updated if that branch is moved
+        */
 #define EXCEPTION_STUB(loc, label)                                      \
         . = interrupt_base_book3e + loc;                                \
         nop;    /* To make debug interrupts happy */                    \
diff --git a/arch/powerpc/mm/tlb_nohash.c b/arch/powerpc/mm/tlb_nohash.c
index e81d5d67f834..2ce42bf1f67e 100644
--- a/arch/powerpc/mm/tlb_nohash.c
+++ b/arch/powerpc/mm/tlb_nohash.c
@@ -391,10 +391,15 @@ static void __early_init_mmu(int boot_cpu)
                 /* Check if HW loader is supported */
                 if ((tlb0cfg & TLBnCFG_IND) &&
                     (tlb0cfg & TLBnCFG_PT)) {
-                        patch_branch(ibase + (0x1c0 / 4),
-                             (unsigned long)&exc_data_tlb_miss_htw_book3e, 0);
-                        patch_branch(ibase + (0x1e0 / 4),
-                             (unsigned long)&exc_instruction_tlb_miss_htw_book3e, 0);
+                        /* Our exceptions vectors start with a NOP and -then- a branch
+                         * to deal with single stepping from userspace which stops on
+                         * the second instruction. Thus we need to patch the second
+                         * instruction of the exception, not the first one
+                         */
+                        patch_branch(ibase + (0x1c0 / 4) + 1,
+                                (unsigned long)&exc_data_tlb_miss_htw_book3e, 0);
+                        patch_branch(ibase + (0x1e0 / 4) + 1,
+                                (unsigned long)&exc_instruction_tlb_miss_htw_book3e, 0);
                         book3e_htw_enabled = 1;
                 }
                 pr_info("MMU: Book3E Page Tables %s\n",