1 files changed, 20 insertions, 4 deletions

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 274a86d001c7..8a0292dbb5fc 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -439,9 +439,9 @@ BEGIN_FTR_SECTION
          * R9           = CR
          * Original R9 to R13 is saved on PACA_EXMC
          *
-         * Switch to mc_emergency stack and handle re-entrancy (though we
-         * currently don't test for overflow). Save MCE registers srr1,
-         * srr0, dar and dsisr and then set ME=1
+         * Switch to mc_emergency stack and handle re-entrancy (we limit
+         * the nested MCE upto level 4 to avoid stack overflow).
+         * Save MCE registers srr1, srr0, dar and dsisr and then set ME=1
          *
          * We use paca->in_mce to check whether this is the first entry or
          * nested machine check. We increment paca->in_mce to track nested
@@ -464,6 +464,9 @@ BEGIN_FTR_SECTION
 0:      subi    r1,r1,INT_FRAME_SIZE    /* alloc stack frame */
         addi    r10,r10,1               /* increment paca->in_mce */
         sth     r10,PACA_IN_MCE(r13)
+        /* Limit nested MCE to level 4 to avoid stack overflow */
+        cmpwi   r10,4
+        bgt     2f                      /* Check if we hit limit of 4 */
         std     r11,GPR1(r1)            /* Save r1 on the stack. */
         std     r11,0(r1)               /* make stack chain pointer */
         mfspr   r11,SPRN_SRR0           /* Save SRR0 */
@@ -482,10 +485,23 @@ BEGIN_FTR_SECTION
         ori     r11,r11,MSR_RI          /* turn on RI bit */
         ld      r12,PACAKBASE(r13)      /* get high part of &label */
         LOAD_HANDLER(r12, machine_check_handle_early)
-        mtspr   SPRN_SRR0,r12
+1:      mtspr   SPRN_SRR0,r12
         mtspr   SPRN_SRR1,r11
         rfid
         b       .       /* prevent speculative execution */
+2:
+        /* Stack overflow. Stay on emergency stack and panic.
+         * Keep the ME bit off while panic-ing, so that if we hit
+         * another machine check we checkstop.
+         */
+        addi    r1,r1,INT_FRAME_SIZE    /* go back to previous stack frame */
+        ld      r11,PACAKMSR(r13)
+        ld      r12,PACAKBASE(r13)
+        LOAD_HANDLER(r12, unrecover_mce)
+        li      r10,MSR_ME
+        andc    r11,r11,r10             /* Turn off MSR_ME */
+        b       1b
+        b       .       /* prevent speculative execution */
 END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)
 
 machine_check_pSeries: