[patch 05/10] x86/traps: Document do_spurious_interrupt_bug()

Thomas Gleixner
2020-02-25T23:25:51Z

Add a comment which explains why this empty handler for a reserved vector
exists.

Requested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.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