[POWERPC] Fix handling of unrecoverable SLB miss interrupts

If an SLB miss interrupt happens while the RI bit of MSR is zero, we
can't just return, because RI being zero indicates that SRR0/SRR1
potentially had live values in them, and the process of taking an
interrupt overwrites them.

This should never happen, but if it does, we try to print a nice oops
message.  That doesn't work, however, because the code at unrecov_slb
assumes that the MMU has been turned on, but we call it with the MMU
off (and have done so since the SLB miss handler was rewritten to run
without turning the MMU on) -- except on iSeries, where everything runs
with the MMU on.

This fixes it by adding the necessary code to turn the MMU on if
necessary.

Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 17 insertions, 1 deletions

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index d3aee08e6814..43a38d89eafc 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -621,7 +621,7 @@ END_FW_FTR_SECTION_IFSET(FW_FEATURE_ISERIES)
         mtlr    r10
 
         andi.   r10,r12,MSR_RI  /* check for unrecoverable exception */
-        beq-    unrecov_slb
+        beq-    2f
 
 .machine        push
 .machine        "power4"
@@ -643,6 +643,22 @@ END_FW_FTR_SECTION_IFSET(FW_FEATURE_ISERIES)
         rfid
         b       .       /* prevent speculative execution */
 
+2:
+#ifdef CONFIG_PPC_ISERIES
+BEGIN_FW_FTR_SECTION
+        b       unrecov_slb
+END_FW_FTR_SECTION_IFSET(FW_FEATURE_ISERIES)
+#endif /* CONFIG_PPC_ISERIES */
+        mfspr   r11,SPRN_SRR0
+        clrrdi  r10,r13,32
+        LOAD_HANDLER(r10,unrecov_slb)
+        mtspr   SPRN_SRR0,r10
+        mfmsr   r10
+        ori     r10,r10,MSR_IR|MSR_DR|MSR_RI
+        mtspr   SPRN_SRR1,r10
+        rfid
+        b       .
+
 unrecov_slb:
         EXCEPTION_PROLOG_COMMON(0x4100, PACA_EXSLB)
         DISABLE_INTS