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Message-Id: <20200225220216.624165786@linutronix.de>
Date: Tue, 25 Feb 2020 22:36:41 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: x86@...nel.org, Steven Rostedt <rostedt@...dmis.org>,
Brian Gerst <brgerst@...il.com>,
Juergen Gross <jgross@...e.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Arnd Bergmann <arnd@...db.de>,
Josh Poimboeuf <jpoimboe@...hat.com>
Subject: [patch 05/10] x86/traps: Document do_spurious_interrupt_bug()
Add a comment which explains why this empty handler for a reserved vector
exists.
Requested-by: Josh Poimboeuf <jpoimboe@...hat.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
arch/x86/kernel/traps.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -862,6 +862,25 @@ do_simd_coprocessor_error(struct pt_regs
dotraplinkage void
do_spurious_interrupt_bug(struct pt_regs *regs, long error_code)
{
+ /*
+ * This addresses a Pentium Pro Erratum:
+ *
+ * PROBLEM: If the APIC subsystem is configured in mixed mode with
+ * Virtual Wire mode implemented through the local APIC, an
+ * interrupt vector of 0Fh (Intel reserved encoding) may be
+ * generated by the local APIC (Int 15). This vector may be
+ * generated upon receipt of a spurious interrupt (an interrupt
+ * which is removed before the system receives the INTA sequence)
+ * instead of the programmed 8259 spurious interrupt vector.
+ *
+ * IMPLICATION: The spurious interrupt vector programmed in the
+ * 8259 is normally handled by an operating system's spurious
+ * interrupt handler. However, a vector of 0Fh is unknown to some
+ * operating systems, which would crash if this erratum occurred.
+ *
+ * In theory this could be limited to 32bit, but the handler is not
+ * hurting and who knows which other CPUs suffer from this.
+ */
}
dotraplinkage void
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