x86/apic: Fix x2apic enablement without interrupt remapping

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Currently, Linux as a hypervisor guest will enable x2apic only if there are
no CPUs present at boot time with an APIC ID above 255.

Hotplugging a CPU later with a higher APIC ID would result in a CPU which
cannot be targeted by external interrupts.

Add a filter in x2apic_apic_id_valid() which can be used to prevent such
CPUs from coming online, and allow x2apic to be enabled even if they are
present at boot time.

Fixes: ce69a78450 ("x86/apic: Enable x2APIC without interrupt remapping under KVM")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201024213535.443185-2-dwmw2@infradead.org

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David Woodhouse 2020-10-24 22:35:01 +01:00 • committed by Thomas Gleixner

parent 5a169bf04c

commit 26573a9774

3 changed files with 18 additions and 6 deletions

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1

arch/x86/include/asm/apic.h

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14

arch/x86/kernel/apic/apic.c

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9

arch/x86/kernel/apic/x2apic_phys.c

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