xen/x86: properly retrieve NMI reason

["Jan Beulich" <JBeulich@suse.com>]

Using the native code here can't work properly, as the hypervisor would
normally have cleared the two reason bits by the time Dom0 gets to see
the NMI (if passed to it at all). There's a shared info field for this,
and there's an existing hook to use - just fit the two together. Note
that the hook can (and should) be used irrespective of whether being in
Dom0, as accessing port 0x61 in a DomU would be even worse, while the
shared info field would just hold zero all the time.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
 arch/x86/xen/enlighten.c    |   22 +++++++++++++++++-
 include/xen/interface/nmi.h |   52 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 73 insertions(+), 1 deletion(-)

--- 3.18/arch/x86/xen/enlighten.c
+++ 3.18-xen-x86-NMI-reason/arch/x86/xen/enlighten.c
@@ -40,6 +40,7 @@
 #include <xen/interface/physdev.h>
 #include <xen/interface/vcpu.h>
 #include <xen/interface/memory.h>
+#include <xen/interface/nmi.h>
 #include <xen/interface/xen-mca.h>
 #include <xen/features.h>
 #include <xen/page.h>
@@ -66,6 +67,7 @@
 #include <asm/reboot.h>
 #include <asm/stackprotector.h>
 #include <asm/hypervisor.h>
+#include <asm/mach_traps.h>
 #include <asm/mwait.h>
 #include <asm/pci_x86.h>
 #include <asm/pat.h>
@@ -1357,6 +1359,21 @@ static const struct machine_ops xen_mach
 	.emergency_restart = xen_emergency_restart,
 };
 
+static unsigned char xen_get_nmi_reason(void)
+{
+	unsigned char reason = 0;
+
+	/* Construct a value which looks like it came from port 0x61. */
+	if (test_bit(_XEN_NMIREASON_io_error,
+		     &HYPERVISOR_shared_info->arch.nmi_reason))
+		reason |= NMI_REASON_IOCHK;
+	if (test_bit(_XEN_NMIREASON_pci_serr,
+		     &HYPERVISOR_shared_info->arch.nmi_reason))
+		reason |= NMI_REASON_SERR;
+
+	return reason;
+}
+
 static void __init xen_boot_params_init_edd(void)
 {
 #if IS_ENABLED(CONFIG_EDD)
@@ -1541,9 +1558,12 @@ asmlinkage __visible void __init xen_sta
 	pv_info = xen_info;
 	pv_init_ops = xen_init_ops;
 	pv_apic_ops = xen_apic_ops;
-	if (!xen_pvh_domain())
+	if (!xen_pvh_domain()) {
 		pv_cpu_ops = xen_cpu_ops;
 
+		x86_platform.get_nmi_reason = xen_get_nmi_reason;
+	}
+
 	if (xen_feature(XENFEAT_auto_translated_physmap))
 		x86_init.resources.memory_setup = xen_auto_xlated_memory_setup;
 	else
--- /usr/local/src/linux-3.18/include/xen/interface/nmi.h	1970-01-01 01:00:00.000000000 +0100
+++ 3.18-xen-x86-NMI-reason/include/xen/interface/nmi.h
@@ -0,0 +1,52 @@
+/******************************************************************************
+ * nmi.h
+ * 
+ * NMI callback registration and reason codes.
+ * 
+ * Copyright (c) 2005, Keir Fraser <keir@xensource.com>
+ */
+
+#ifndef __XEN_PUBLIC_NMI_H__
+#define __XEN_PUBLIC_NMI_H__
+
+#include <xen/interface/xen.h>
+
+/*
+ * NMI reason codes:
+ * Currently these are x86-specific, stored in arch_shared_info.nmi_reason.
+ */
+ /* I/O-check error reported via ISA port 0x61, bit 6. */
+#define _XEN_NMIREASON_io_error     0
+#define XEN_NMIREASON_io_error      (1UL << _XEN_NMIREASON_io_error)
+ /* PCI SERR reported via ISA port 0x61, bit 7. */
+#define _XEN_NMIREASON_pci_serr     1
+#define XEN_NMIREASON_pci_serr      (1UL << _XEN_NMIREASON_pci_serr)
+ /* Unknown hardware-generated NMI. */
+#define _XEN_NMIREASON_unknown      2
+#define XEN_NMIREASON_unknown       (1UL << _XEN_NMIREASON_unknown)
+
+/*
+ * long nmi_op(unsigned int cmd, void *arg)
+ * NB. All ops return zero on success, else a negative error code.
+ */
+
+/*
+ * Register NMI callback for this (calling) VCPU. Currently this only makes
+ * sense for domain 0, vcpu 0. All other callers will be returned EINVAL.
+ * arg == pointer to xennmi_callback structure.
+ */
+#define XENNMI_register_callback   0
+struct xennmi_callback {
+    unsigned long handler_address;
+    unsigned long pad;
+};
+typedef struct xennmi_callback xennmi_callback_t;
+DEFINE_XEN_GUEST_HANDLE(xennmi_callback_t);
+
+/*
+ * Deregister NMI callback for this (calling) VCPU.
+ * arg == NULL.
+ */
+#define XENNMI_unregister_callback 1
+
+#endif /* __XEN_PUBLIC_NMI_H__ */