Messages in this thread | | | Date | Mon, 16 Jan 2017 18:13:39 -0500 | From | Prarit Bhargava <> | Subject | Re: [PATCH] x86/mce: Fix initialization error warning |
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On 01/16/2017 05:43 PM, Borislav Petkov wrote: > On Mon, Jan 16, 2017 at 05:06:02PM -0500, Prarit Bhargava wrote: >> Yes, it was loud enough to generate a bug report from a user. > > Yeah, because all users are sane and we should do whatever they want - > no questions asked. Especially those who boot with "mce=off". > > Did you actually ask that user why she/he is even booting with > "mce=off"?
Yes, mce=off is the default for kdump:
KDUMP_COMMANDLINE_APPEND="irqpoll nr_cpus=1 reset_devices cgroup_disable=memory mce=off numa=off udev.children-max=2 panic=10 rootflags=nofail acpi_no_memhotplug transparent_hugepage=never"
There is a race condition between NMI completing on a CPU and the MCE synchronization timing out that results in a kernel panic on the kdump kernel, and a loss of the dump image. There have been a few attempts to fix it over the years. It seems as simple as setting a flag in native_machine_crash_shutdown() and querying it in do_machine_check() to avoid mce & nmi race.
P.
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