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>

1 files changed, 20 insertions, 1 deletions

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 034b7eaf68d2..bffec73dbffc 100644
--- 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