powerpc/pseries: PACA save area fix for MCE vs MCE

MCE must not enable MSR_RI until PACA_EXMC is no longer being used.

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

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 034b7ea..bffec73 100644 (file)
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -485,7 +485,23 @@ machine_check_fwnmi:
        EXCEPTION_PROLOG_0(PACA_EXMC)
 machine_check_pSeries_0:
        EXCEPTION_PROLOG_1(PACA_EXMC, KVMTEST, 0x200)
-       EXCEPTION_PROLOG_PSERIES_1(machine_check_common, EXC_STD)
+       /*
+        * The following is essentially EXCEPTION_PROLOG_PSERIES_1 with the
+        * difference that MSR_RI is not enabled, because PACA_EXMC is being
+        * used, so nested machine check corrupts it. machine_check_common
+        * enables MSR_RI.
+        */
+       ld      r12,PACAKBASE(r13)
+       ld      r10,PACAKMSR(r13)
+       xori    r10,r10,MSR_RI
+       mfspr   r11,SPRN_SRR0
+       LOAD_HANDLER(r12, machine_check_common)
+       mtspr   SPRN_SRR0,r12
+       mfspr   r12,SPRN_SRR1
+       mtspr   SPRN_SRR1,r10
+       rfid
+       b       .       /* prevent speculative execution */
+
        KVM_HANDLER_SKIP(PACA_EXMC, EXC_STD, 0x200)
        KVM_HANDLER_SKIP(PACA_EXGEN, EXC_STD, 0x300)
        KVM_HANDLER_SKIP(PACA_EXSLB, EXC_STD, 0x380)
@@ -977,6 +993,9 @@ machine_check_common:
        RECONCILE_IRQ_STATE(r10, r11)
        ld      r3,PACA_EXMC+EX_DAR(r13)
        lwz     r4,PACA_EXMC+EX_DSISR(r13)
+       /* Enable MSR_RI when finished with PACA_EXMC */
+       li      r10,MSR_RI
+       mtmsrd  r10,1
        std     r3,_DAR(r1)
        std     r4,_DSISR(r1)
        bl      save_nvgprs