powerpc: Fix 64-bit BookE FP unavailable exceptions

We were using CR0.EQ after EXCEPTION_COMMON, hoping it still
contained whether we came from userspace or kernel space.

However, under some circumstances, EXCEPTION_COMMON will
call C code and clobber non-volatile registers, so we really
need to re-load the previous MSR from the stackframe and
re-test.

While there, invert the condition to make the fast path more
obvious and remove the BUG_OPCODE which was a debugging
leftover and call .ret_from_except as we should.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 7 insertions, 6 deletions

diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S
index 3de9993c5c65..c4c34665c221 100644
--- a/arch/powerpc/kernel/exceptions-64e.S
+++ b/arch/powerpc/kernel/exceptions-64e.S
@@ -353,15 +353,16 @@ interrupt_end_book3e:
         NORMAL_EXCEPTION_PROLOG(0x800, PROLOG_ADDITION_NONE)
         /* we can probably do a shorter exception entry for that one... */
         EXCEPTION_COMMON(0x800, PACA_EXGEN, INTS_KEEP)
-        bne     1f                      /* if from user, just load it up */
-        INTS_DISABLE_ALL
+        ld      r12,_MSR(r1)
+        andi.   r0,r12,MSR_PR;
+        beq-    1f
+        bl      .load_up_fpu
+        b       fast_exception_return
+1:      INTS_DISABLE_ALL
         bl      .save_nvgprs
         addi    r3,r1,STACK_FRAME_OVERHEAD
         bl      .kernel_fp_unavailable_exception
-        BUG_OPCODE
-1:      ld      r12,_MSR(r1)
-        bl      .load_up_fpu
-        b       fast_exception_return
+        b       .ret_from_except
 
 /* Decrementer Interrupt */
         MASKABLE_EXCEPTION(0x900, decrementer, .timer_interrupt, ACK_DEC)