powerpc/64s: Fix unrecoverable MCE calling async handler from NMI

[ Upstream commit f08fb25bc66986b0952724530a640d9970fa52c1 ]

The machine check handler is not considered NMI on 64s. The early
handler is the true NMI handler, and then it schedules the
machine_check_exception handler to run when interrupts are enabled.

This works fine except the case of an unrecoverable MCE, where the true
NMI is taken when MSR[RI] is clear, it can not recover, so it calls
machine_check_exception directly so something might be done about it.

Calling an async handler from NMI context can result in irq state and
other things getting corrupted. This can also trigger the BUG at
  arch/powerpc/include/asm/interrupt.h:168
  BUG_ON(!arch_irq_disabled_regs(regs) && !(regs->msr & MSR_EE));

Fix this by making an _async version of the handler which is called
in the normal case, and a NMI version that is called for unrecoverable
interrupts.

Fixes: 2b43dd7653cc ("powerpc/64: enable MSR[EE] in irq replay pt_regs")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Tested-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211004145642.1331214-6-npiggin@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/powerpc/include/asm/interrupt.h b/arch/powerpc/include/asm/interrupt.h
index 6b800d3e2681f6082a163b24d63a2be06f2f275d..a925dbc5833c7bd1433086aa696b269bf4cc9d96 100644 (file)
--- a/arch/powerpc/include/asm/interrupt.h
+++ b/arch/powerpc/include/asm/interrupt.h
@@ -525,10 +525,9 @@ static __always_inline long ____##func(struct pt_regs *regs)
 /* kernel/traps.c */
 DECLARE_INTERRUPT_HANDLER_NMI(system_reset_exception);
 #ifdef CONFIG_PPC_BOOK3S_64
-DECLARE_INTERRUPT_HANDLER_ASYNC(machine_check_exception);
-#else
-DECLARE_INTERRUPT_HANDLER_NMI(machine_check_exception);
+DECLARE_INTERRUPT_HANDLER_ASYNC(machine_check_exception_async);
 #endif
+DECLARE_INTERRUPT_HANDLER_NMI(machine_check_exception);
 DECLARE_INTERRUPT_HANDLER(SMIException);
 DECLARE_INTERRUPT_HANDLER(handle_hmi_exception);
 DECLARE_INTERRUPT_HANDLER(unknown_exception);

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 024d9231f88c39a10f85acd81cafc38dc3fdb82b..eaf1f72131a18f8f6a376c332619ab0e00ecda7a 100644 (file)
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -1243,7 +1243,7 @@ EXC_COMMON_BEGIN(machine_check_common)
        li      r10,MSR_RI
        mtmsrd  r10,1
        addi    r3,r1,STACK_FRAME_OVERHEAD
-       bl      machine_check_exception
+       bl      machine_check_exception_async
        b       interrupt_return_srr
 
 
@@ -1303,7 +1303,11 @@ END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)
        subi    r12,r12,1
        sth     r12,PACA_IN_MCE(r13)
 
-       /* Invoke machine_check_exception to print MCE event and panic. */
+       /*
+        * Invoke machine_check_exception to print MCE event and panic.
+        * This is the NMI version of the handler because we are called from
+        * the early handler which is a true NMI.
+        */
        addi    r3,r1,STACK_FRAME_OVERHEAD
        bl      machine_check_exception
 

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 4ac85ab15ad76a8d2369d241e472a7bad467e158..08356ec9bfed428dc6c379037e8838dbba9f04e6 100644 (file)
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -797,24 +797,22 @@ void die_mce(const char *str, struct pt_regs *regs, long err)
         * do_exit() checks for in_interrupt() and panics in that case, so
         * exit the irq/nmi before calling die.
         */
-       if (IS_ENABLED(CONFIG_PPC_BOOK3S_64))
-               irq_exit();
-       else
+       if (in_nmi())
                nmi_exit();
+       else
+               irq_exit();
        die(str, regs, err);
 }
 
 /*
- * BOOK3S_64 does not call this handler as a non-maskable interrupt
+ * BOOK3S_64 does not usually call this handler as a non-maskable interrupt
  * (it uses its own early real-mode handler to handle the MCE proper
  * and then raises irq_work to call this handler when interrupts are
- * enabled).
+ * enabled). The only time when this is not true is if the early handler
+ * is unrecoverable, then it does call this directly to try to get a
+ * message out.
  */
-#ifdef CONFIG_PPC_BOOK3S_64
-DEFINE_INTERRUPT_HANDLER_ASYNC(machine_check_exception)
-#else
-DEFINE_INTERRUPT_HANDLER_NMI(machine_check_exception)
-#endif
+static void __machine_check_exception(struct pt_regs *regs)
 {
        int recover = 0;
 
@@ -848,12 +846,19 @@ bail:
        /* Must die if the interrupt is not recoverable */
        if (!(regs->msr & MSR_RI))
                die_mce("Unrecoverable Machine check", regs, SIGBUS);
+}
 
 #ifdef CONFIG_PPC_BOOK3S_64
-       return;
-#else
-       return 0;
+DEFINE_INTERRUPT_HANDLER_ASYNC(machine_check_exception_async)
+{
+       __machine_check_exception(regs);
+}
 #endif
+DEFINE_INTERRUPT_HANDLER_NMI(machine_check_exception)
+{
+       __machine_check_exception(regs);
+
+       return 0;
 }
 
 DEFINE_INTERRUPT_HANDLER(SMIException) /* async? */