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x86/smp: Use dedicated cache-line for mwait_play_dead()
commit f9c9987 upstream. Monitoring idletask::thread_info::flags in mwait_play_dead() has been an obvious choice as all what is needed is a cache line which is not written by other CPUs. But there is a use case where a "dead" CPU needs to be brought out of MWAIT: kexec(). This is required as kexec() can overwrite text, pagetables, stacks and the monitored cacheline of the original kernel. The latter causes MWAIT to resume execution which obviously causes havoc on the kexec kernel which results usually in triple faults. Use a dedicated per CPU storage to prepare for that. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Ashok Raj <ashok.raj@intel.com> Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de> Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20230615193330.434553750@linutronix.de Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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