On Thu, Feb 27, 2014 at 09:57:26PM -0500, Steven Rostedt wrote:
> @@ -512,8 +508,21 @@ static inline void nmi_nesting_postprocess(void)
> dotraplinkage notrace __kprobes void
> do_nmi(struct pt_regs *regs, long error_code)
> {
> + unsigned long cr2;
> +
> nmi_nesting_preprocess(regs);
>
> + /*
> + * Save off the CR2 register. If we take a page fault in the NMI then
> + * it could corrupt the CR2 value. If the NMI preempts a page fault
> + * handler before it was able to read the CR2 register, and then the
> + * NMI itself takes a page fault, the page fault that was preempted
> + * will read the information from the NMI page fault and not the
> + * origin fault. Save it off and restore it if it changes.
> + * Use the r12 callee-saved register.
You might want to make that line go away :-)
> + */
> + cr2 = read_cr2();
> +
> nmi_enter();
>
> inc_irq_stat(__nmi_count);
> @@ -523,6 +532,10 @@ do_nmi(struct pt_regs *regs, long error_code)
>
> nmi_exit();
>
> + /* Reads are cheaper than writes */
> + if (unlikely(cr2 != read_cr2()))
> + write_cr2(cr2);
> +
> /* On i386, may loop back to preprocess */
> nmi_nesting_postprocess();
> }
--
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