System Reset, being an NMI, must return more carefully than other
interrupts. It has traditionally returned via the nromal return
from exception path, but that has a number of problems.
- r13 does not get restored if returning to kernel. This is for
interrupts which may cause a context switch, which sreset will
never do. Interrupting OPAL (which uses a different r13) is one
place where this causes breakage.
- It may cause several other problems returning to kernel with
preempt or TIF_EMULATE_STACK_STORE if it hits at the wrong time.
It's safer just to have a simple restore and return, like machine
check which is the other NMI.
Signed-off-by: Nicholas Piggin <npig...@gmail.com>
---
arch/powerpc/kernel/exceptions-64s.S | 61 ++++++++++++++++++++++++++++++++++--
1 file changed, 58 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/kernel/exceptions-64s.S
b/arch/powerpc/kernel/exceptions-64s.S
index 3ac87e53b3da..114ff7170562 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -139,6 +139,21 @@ EXC_COMMON_BEGIN(system_reset_idle_common)
b pnv_powersave_wakeup
#endif
+/*
+ * Set IRQS_ALL_DISABLED unconditionally so arch_irqs_disabled does
+ * the right thing. We do not want to reconcile because that goes
+ * through irq tracing which we don't want in NMI.
+ *
+ * Save PACAIRQHAPPENED because some code will do a hard disable
+ * (e.g., xmon). So we want to restore this back to where it was
+ * when we return. DAR is unused in the stack, so save it there.
+ */
+#define ADD_RECONCILE_NMI \
+ li r10,IRQS_ALL_DISABLED; \
+ stb r10,PACAIRQSOFTMASK(r13); \
+ lbz r10,PACAIRQHAPPENED(r13); \
+ std r10,_DAR(r1)
+
EXC_COMMON_BEGIN(system_reset_common)
/*
* Increment paca->in_nmi then enable MSR_RI. SLB or MCE will be able
@@ -157,16 +172,56 @@ EXC_COMMON_BEGIN(system_reset_common)
subi r1,r1,INT_FRAME_SIZE
EXCEPTION_COMMON_NORET_STACK(PACA_EXNMI, 0x100,
system_reset, system_reset_exception,
- ADD_NVGPRS;ADD_RECONCILE)
+ ADD_NVGPRS;ADD_RECONCILE_NMI)
+
+ /* This (and MCE) can be simplified with mtmsrd L=1 */
+ /* Clear MSR_RI before setting SRR0 and SRR1. */
+ li r0,MSR_RI
+ mfmsr r9
+ andc r9,r9,r0
+ mtmsrd r9,1
/*
- * The stack is no longer in use, decrement in_nmi.
+ * MSR_RI is clear, now we can decrement paca->in_nmi.
*/
lhz r10,PACA_IN_NMI(r13)
subi r10,r10,1
sth r10,PACA_IN_NMI(r13)
- b ret_from_except
+ /*
+ * Restore soft mask settings.
+ */
+ ld r10,_DAR(r1)
+ stb r10,PACAIRQHAPPENED(r13)
+ ld r10,SOFTE(r1)
+ stb r10,PACAIRQSOFTMASK(r13)
+
+ /*
+ * Keep below code in synch with MACHINE_CHECK_HANDLER_WINDUP.
+ * Should share common bits...
+ */
+
+ /* Move original SRR0 and SRR1 into the respective regs */
+ ld r9,_MSR(r1)
+ mtspr SPRN_SRR1,r9
+ ld r3,_NIP(r1)
+ mtspr SPRN_SRR0,r3
+ ld r9,_CTR(r1)
+ mtctr r9
+ ld r9,_XER(r1)
+ mtxer r9
+ ld r9,_LINK(r1)
+ mtlr r9
+ REST_GPR(0, r1)
+ REST_8GPRS(2, r1)
+ REST_GPR(10, r1)
+ ld r11,_CCR(r1)
+ mtcr r11
+ REST_GPR(11, r1)
+ REST_2GPRS(12, r1)
+ /* restore original r1. */
+ ld r1,GPR1(r1)
+ RFI_TO_USER_OR_KERNEL
#ifdef CONFIG_PPC_PSERIES
/*
--
2.16.1
