[PATCH v4 11/16] powerpc/64s: machine check interrupt update NMI accounting

[Nicholas Piggin]

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 <npig...@gmail.com>
---
 arch/powerpc/kernel/mce.c     |  7 +++++++
 arch/powerpc/kernel/process.c |  2 +-
 arch/powerpc/kernel/traps.c   | 14 +++++++++++++-
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/mce.c b/arch/powerpc/kernel/mce.c
index 8077b5fb18a7..be7e3f92a7b5 100644
--- 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/process.c b/arch/powerpc/kernel/process.c
index 9c21288f8645..44410dd3029f 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1421,7 +1421,7 @@ void show_regs(struct pt_regs * regs)
                pr_cont("DAR: "REG" DSISR: %08lx ", regs->dar, regs->dsisr);
 #endif
 #ifdef CONFIG_PPC64
-       pr_cont("IRQMASK: %lx ", regs->softe);
+       pr_cont("IRQMASK: %lx IN_NMI:%d IN_MCE:%d", regs->softe, 
(int)get_paca()->in_nmi, (int)get_paca()->in_mce);
 #endif
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
        if (MSR_TM_ACTIVE(regs->msr))
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 3fca22276bb1..9f6852322e59 100644
--- 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();
 
-- 
2.23.0