[PATCH 2/4] powerpc/64s/interrupt: Perf NMI should not take normal exit path

[Nicholas Piggin]

NMI interrupts should exit with EXCEPTION_RESTORE_REGS not with
interrupt_return_srr, which is what the perf NMI handler currently does.
This breaks if a PMI hits after interrupt_exit_user_prepare_main() has
switched the context tracking to user mode, then the CT_WARN_ON() in
interrupt_exit_kernel_prepare() fires because it returns to kernel with
context set to user.

This could possibly be solved by soft-disabling PMIs in the exit path,
but that reduces our ability to profile that code. The warning could be
removed, but it's potentially useful.

All other NMIs and soft-NMIs return using EXCEPTION_RESTORE_REGS, so
this makes perf interrupts consistent with that and seems like the best
fix.

Signed-off-by: Nicholas Piggin <npig...@gmail.com>
---
 arch/powerpc/kernel/exceptions-64s.S | 14 +++++++++++++-
 arch/powerpc/kernel/traps.c          |  2 --
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/exceptions-64s.S 
b/arch/powerpc/kernel/exceptions-64s.S
index 5381a43e50fe..651c36b056bd 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -2357,9 +2357,21 @@ EXC_VIRT_END(performance_monitor, 0x4f00, 0x20)
 EXC_COMMON_BEGIN(performance_monitor_common)
        GEN_COMMON performance_monitor
        addi    r3,r1,STACK_FRAME_OVERHEAD
-       bl      performance_monitor_exception
+       lbz     r4,PACAIRQSOFTMASK(r13)
+       cmpdi   r4,IRQS_ENABLED
+       bne     1f
+       bl      performance_monitor_exception_async
        b       interrupt_return_srr
+1:
+       bl      performance_monitor_exception_nmi
+       /* Clear MSR_RI before setting SRR0 and SRR1. */
+       li      r9,0
+       mtmsrd  r9,1
 
+       kuap_kernel_restore r9, r10
+
+       EXCEPTION_RESTORE_REGS hsrr=0
+       RFI_TO_KERNEL
 
 /**
  * Interrupt 0xf20 - Vector Unavailable Interrupt.
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 9bdd79aa51cf..6138ee22d06c 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -1899,7 +1899,6 @@ DEFINE_INTERRUPT_HANDLER(vsx_unavailable_tm)
 #endif /* CONFIG_PPC_TRANSACTIONAL_MEM */
 
 #ifdef CONFIG_PPC64
-DECLARE_INTERRUPT_HANDLER_NMI(performance_monitor_exception_nmi);
 DEFINE_INTERRUPT_HANDLER_NMI(performance_monitor_exception_nmi)
 {
        __this_cpu_inc(irq_stat.pmu_irqs);
@@ -1910,7 +1909,6 @@ 
DEFINE_INTERRUPT_HANDLER_NMI(performance_monitor_exception_nmi)
 }
 #endif
 
-DECLARE_INTERRUPT_HANDLER_ASYNC(performance_monitor_exception_async);
 DEFINE_INTERRUPT_HANDLER_ASYNC(performance_monitor_exception_async)
 {
        __this_cpu_inc(irq_stat.pmu_irqs);
-- 
2.37.2