23ce462092
Sending IPI to self or all CPUs does not require write into upper part of the ICR, prone to races. Previously the code disabled interrupts, but it was not enough for NMIs. Instead of that when possible write only lower part of the register, or use special SELF IPI register in x2APIC mode. This also removes ICR reads used to preserve reserved bits on write. It was there from the beginning, but I failed to find explanation why, neither I see Linux doing it. Specification even tells that ICR content may be lost in deep C-states, so if hardware does not bother to preserve it, why should we? MFC after: 2 weeks Sponsored by: iXsystems, Inc.
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