[PATCH v6 21/29] x86/nmi: Add an NMI_WATCHDOG NMI handler category

[Ricardo Neri]

Add a NMI_WATCHDOG as a new category of NMI handler. This new category
is to be used with the HPET-based hardlockup detector. This detector
does not have a direct way of checking if the HPET timer is the source of
the NMI. Instead, it indirectly estimates it using the time-stamp counter.

Therefore, we may have false-positives in case another NMI occurs within
the estimated time window. For this reason, we want the handler of the
detector to be called after all the NMI_LOCAL handlers. A simple way
of achieving this with a new NMI handler category.

Cc: Andi Kleen <a...@linux.intel.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: "Ravi V. Shankar" <ravi.v.shan...@intel.com>
Cc: Stephane Eranian <eran...@google.com>
Cc: io...@lists.linux-foundation.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: x...@kernel.org
Reviewed-by: Tony Luck <tony.l...@intel.com>
Signed-off-by: Ricardo Neri <ricardo.neri-calde...@linux.intel.com>
---
Changes since v5:
 * Updated to call instrumentation_end() as per f051f6979550 ("x86/nmi:
   Protect NMI entry against instrumentation")

Changes since v4:
 * None

Changes since v3:
 * None

Changes since v2:
 * Introduced this patch.

Changes since v1:
 * N/A
---
 arch/x86/include/asm/nmi.h |  1 +
 arch/x86/kernel/nmi.c      | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/arch/x86/include/asm/nmi.h b/arch/x86/include/asm/nmi.h
index 1cb9c17a4cb4..4a0d5b562c91 100644
--- a/arch/x86/include/asm/nmi.h
+++ b/arch/x86/include/asm/nmi.h
@@ -28,6 +28,7 @@ enum {
        NMI_UNKNOWN,
        NMI_SERR,
        NMI_IO_CHECK,
+       NMI_WATCHDOG,
        NMI_MAX
 };
 
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index e73f7df362f5..fde387e0812a 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -61,6 +61,10 @@ static struct nmi_desc nmi_desc[NMI_MAX] =
                .lock = __RAW_SPIN_LOCK_UNLOCKED(&nmi_desc[3].lock),
                .head = LIST_HEAD_INIT(nmi_desc[3].head),
        },
+       {
+               .lock = __RAW_SPIN_LOCK_UNLOCKED(&nmi_desc[4].lock),
+               .head = LIST_HEAD_INIT(nmi_desc[4].head),
+       },
 
 };
 
@@ -168,6 +172,8 @@ int __register_nmi_handler(unsigned int type, struct 
nmiaction *action)
         */
        WARN_ON_ONCE(type == NMI_SERR && !list_empty(&desc->head));
        WARN_ON_ONCE(type == NMI_IO_CHECK && !list_empty(&desc->head));
+       WARN_ON_ONCE(type == NMI_WATCHDOG && !list_empty(&desc->head));
+
 
        /*
         * some handlers need to be executed first otherwise a fake
@@ -379,6 +385,10 @@ static noinstr void default_do_nmi(struct pt_regs *regs)
        }
        raw_spin_unlock(&nmi_reason_lock);
 
+       handled = nmi_handle(NMI_WATCHDOG, regs);
+       if (handled == NMI_HANDLED)
+               goto out;
+
        /*
         * Only one NMI can be latched at a time.  To handle
         * this we may process multiple nmi handlers at once to
-- 
2.17.1