powerpc/64s/exception: machine check improve labels and comments

Short forward and backward branches can be given number labels,
but larger significant divergences in code path a more readable
if they're given descriptive names.

Also adjusts a comment to account for guest delivery.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190802105709.27696-17-npiggin@gmail.com

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 3a7f180..c2474c9 100644 (file)
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -1052,7 +1052,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HVMODE | CPU_FTR_ARCH_206)
         */
        lbz     r11,HSTATE_IN_GUEST(r13)
        cmpwi   r11,0                   /* Check if coming from guest */
-       bne     9f                      /* continue if we are. */
+       bne     mce_deliver             /* continue if we are. */
 #endif
 
        /*
@@ -1060,7 +1060,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HVMODE | CPU_FTR_ARCH_206)
         * exception handler which will deliver the MC event to this kernel.
         */
        andi.   r11,r12,MSR_PR          /* See if coming from user. */
-       bne     9f                      /* continue in V mode if we are. */
+       bne     mce_deliver             /* continue in V mode if we are. */
 
        /*
         * At this point we are coming from kernel context.
@@ -1088,8 +1088,14 @@ END_FTR_SECTION_IFSET(CPU_FTR_HVMODE | CPU_FTR_ARCH_206)
        MACHINE_CHECK_HANDLER_WINDUP
        RFI_TO_KERNEL
 
-9:
-       /* Deliver the machine check to host kernel in V mode. */
+mce_deliver:
+       /*
+        * This is a host user or guest MCE. Restore all registers, then
+        * run the "late" handler. For host user, this will run the
+        * machine_check_exception handler in virtual mode like a normal
+        * interrupt handler. For guest, this will trigger the KVM test
+        * and branch to the KVM interrupt similarly to other interrupts.
+        */
 BEGIN_FTR_SECTION
        ld      r10,ORIG_GPR3(r1)
        mtspr   SPRN_CFAR,r10