powerpc/64s: machine check interrupt update NMI accounting

machine_check_early() is taken as an NMI, so nmi_enter() is used
there. machine_check_exception() is no longer taken as an NMI (it's
invoked via irq_work in the case a machine check hits in kernel mode),
so remove the nmi_enter() from that case.

In NMI context, hash faults don't try to refill the hash table, which
can lead to crashes accessing non-pinned kernel pages. System reset
still has this potential problem.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Drop change in show_regs() which breaks Book3E]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200508043408.886394-12-npiggin@gmail.com

diff --git a/arch/powerpc/kernel/mce.c b/arch/powerpc/kernel/mce.c
index 8077b5f..be7e3f9 100644 (file)
--- a/arch/powerpc/kernel/mce.c
+++ b/arch/powerpc/kernel/mce.c
@@ -574,6 +574,9 @@ EXPORT_SYMBOL_GPL(machine_check_print_event_info);
 long machine_check_early(struct pt_regs *regs)
 {
        long handled = 0;
+       bool nested = in_nmi();
+       if (!nested)
+               nmi_enter();
 
        hv_nmi_check_nonrecoverable(regs);
 
@@ -582,6 +585,10 @@ long machine_check_early(struct pt_regs *regs)
         */
        if (ppc_md.machine_check_early)
                handled = ppc_md.machine_check_early(regs);
+
+       if (!nested)
+               nmi_exit();
+
        return handled;
 }
 

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 3fca222..9f68523 100644 (file)
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -823,7 +823,19 @@ int machine_check_generic(struct pt_regs *regs)
 void machine_check_exception(struct pt_regs *regs)
 {
        int recover = 0;
-       bool nested = in_nmi();
+       bool nested;
+
+       /*
+        * BOOK3S_64 does not 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). Set nested = true for this case, which just makes it avoid
+        * the nmi_enter/exit.
+        */
+       if (IS_ENABLED(CONFIG_PPC_BOOK3S_64) || in_nmi())
+               nested = true;
+       else
+               nested = false;
        if (!nested)
                nmi_enter();