[PATCH 4.4 123/192] [PATCH 127/135] x86/hyperv: Avoid reporting bogus NMI status for Gen2 instances

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 1e2ae9ec072f3b7887f456426bc2cf23b80f661a ]

Generation2 instances don't support reporting the NMI status on port 0x61,
read from there returns 'ff' and we end up reporting nonsensical PCI
error (as there is no PCI bus in these instances) on all NMIs:

    NMI: PCI system error (SERR) for reason ff on CPU 0.
    Dazed and confused, but trying to continue

Fix the issue by overriding x86_platform.get_nmi_reason. Use 'booted on
EFI' flag to detect Gen2 instances.

Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Cathy Avery <cavery@xxxxxxxxxx>
Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: devel@xxxxxxxxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1460728232-31433-1-git-send-email-vkuznets@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/x86/kernel/cpu/mshyperv.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -152,6 +152,11 @@ static struct clocksource hyperv_cs = {
 	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
 };
 
+static unsigned char hv_get_nmi_reason(void)
+{
+	return 0;
+}
+
 static void __init ms_hyperv_init_platform(void)
 {
 	/*
@@ -191,6 +196,13 @@ static void __init ms_hyperv_init_platfo
 	machine_ops.crash_shutdown = hv_machine_crash_shutdown;
 #endif
 	mark_tsc_unstable("running on Hyper-V");
+
+	/*
+	 * Generation 2 instances don't support reading the NMI status from
+	 * 0x61 port.
+	 */
+	if (efi_enabled(EFI_BOOT))
+		x86_platform.get_nmi_reason = hv_get_nmi_reason;
 }
 
 const __refconst struct hypervisor_x86 x86_hyper_ms_hyperv = {