Re: [PATCH v9 2/3] trace,x86: add x86 irq vector tracepoints

["H. Peter Anvin" <hpa@zytor.com>]

On 02/04/2013 02:49 PM, Seiji Aguchi wrote:
> +
> +static void switch_to_trace_idt(void *arg)
> +{
> +	store_idt(this_cpu_ptr(&orig_idt_descr));
> +	load_idt(&trace_idt_descr);
> +
> +	return;
> +}
> +
> +static void restore_original_idt(void *arg)
> +{
> +	if (this_cpu_read(orig_idt_descr.address)) {
> +		load_idt(this_cpu_ptr(&orig_idt_descr));
> +		this_cpu_write(orig_idt_descr.address, 0);
> +	}
> +
> +	return;
> +}
> +

The base address of the IDT doesn't generally change... the one
exception is when we do the funny NMI workaround.

For that reason, I would be happier if we just restored the standard
value instead of saving/restoring stuff.

The above code is probably broken if either side is in the funny NMI
zone... unless you can guarantee it is *always* in the funny NMI zone
(in which case you can just load nmi_idt_descr instead.

Steve R., do you know what the constraints are with respect to that?

	-hpa