linux-kernel - recent patch "x86/acpi: Prevent X2APIC id 0xffffffff from being accounted"

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Date:   Fri, 27 Apr 2018 01:21:44 -0600
From:   "Jan Beulich" <JBeulich@...e.com>
To:     <douly.fnst@...fujitsu.com>, <tglx@...utronix.de>
Cc:     <linux-kernel@...r.kernel.org>
Subject: recent patch "x86/acpi: Prevent X2APIC id 0xffffffff from
 being accounted"

Hello,

I've just stumbled across this commit, and I'm wondering if that's actually
correct (I too have at least one system where such IDs are reported in
MADT): For offline/absent CPUs, the firmware may not know the APIC IDs
at the point MADT is built, so I think it is quite reasonable to put ~0 in
there. The ACPID spec specifically calls out that the IDs must not change
across sleep states, which implies to me that they may change across an
offline period of a CPU. IOW I think such entries still need to contribute to
the count of disabled CPUs.

I notice a similar change has been done for the xAPIC case a while ago
by you, Thomas.

Jan