linux-kernel - x86: Spurious vectors not handled robustly

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Message-ID: <e525108f-3749-4e1d-1ac2-0d0a2655f15f@siemens.com>
Date:   Mon, 24 Jun 2019 12:00:00 +0200
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: x86: Spurious vectors not handled robustly

Hi all,

probably since "x86: Avoid building unused IRQ entry stubs" (2414e021ac8d), the 
kernel can no longer tell spurious IRQs by the APIC apart from spuriously 
triggered unused vectors. We've managed to trigger such a cause with the 
Jailhouse hypervisor (incorrectly injected MANAGED_IRQ_SHUTDOWN_VECTOR), and the 
result was not only a misreport of the vector number (0xff instead of 0xef - 
took me a while...), but also stalled interrupts of equal and lower priority 
because a spurious interrupt is not (and must not be) acknowledged.

How to address that best? I would say we should at least have separate entry 
paths for APIC interrupt vs. vectors, to improve robustness in the faulty case.

Jan

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