Re: [patch V2 03/17] x86/traps: Remove pointless irq enable from do_spurious_interrupt_bug()

Thomas Gleixner
2019-10-23T23:18:55Z

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On Wed, 23 Oct 2019, Josh Poimboeuf wrote:
> On Thu, Oct 24, 2019 at 12:35:27AM +0200, Thomas Gleixner wrote:
> > On Wed, 23 Oct 2019, Josh Poimboeuf wrote:
> >
> > > On Wed, Oct 23, 2019 at 02:27:08PM +0200, Thomas Gleixner wrote:
> > > > That function returns immediately after conditionally reenabling interrupts which
> > > > is more than pointless and requires the ASM code to disable interrupts again.
> > > >
> > > > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> > > > ---
> > > > arch/x86/kernel/traps.c | 1 -
> > > > 1 file changed, 1 deletion(-)
> > > >
> > > > --- a/arch/x86/kernel/traps.c
> > > > +++ b/arch/x86/kernel/traps.c
> > > > @@ -871,7 +871,6 @@ do_simd_coprocessor_error(struct pt_regs
> > > > dotraplinkage void
> > > > do_spurious_interrupt_bug(struct pt_regs *regs, long error_code)
> > > > {
> > > > - cond_local_irq_enable(regs);
> > > > }
> > >
> > > I think we can just remove this handler altogether. The Intel and AMD
> > > manuals say vector 15 (X86_TRAP_SPURIOUS) is reserved.
> >
> > Right, but this has history. 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.
> >
> > Initially (2.1.) there was a printk() in that handler, which later got
> > ifdeffed out (2.1.54).
> >
> > So I rather keep that thing at least as long as we support PPro :) Even if
> > we ditch that the handler is not really hurting anyone.
>
> Ah. I guess we could remove the idtentry for 64-bit then? Anyway the
> above would be a good comment for the function.

That doesn't buy much. Who knows how many other CPUs issue vector 15
occasionally and will then crash and burn. Better safe than sorry :)

Thanks,

tglx