Hi Chenggang,
Have a doubt about the old code.
On 2018/4/12 PM 12:58, chenggang.qin@xxxxxxxxxxxxxxxxx Wrote:
> From: Andy Lutomirski <luto@xxxxxxxxxx>
>
> commit: 9d05041679904b12c12421cbcf9cb5f4860a8d7b upstream
>
> 32-bit kernels handle nested NMIs in C. Enable the exact same
> handling on 64-bit kernels as well. This isn't currently
> necessary, but it will become necessary once the asm code starts
> allowing limited nesting.
>
> ......
> -static inline void nmi_nesting_preprocess(struct pt_regs *regs)
> +dotraplinkage notrace void
> +do_nmi(struct pt_regs *regs, long error_code)
> {
> + if (this_cpu_read(nmi_state) != NMI_NOT_RUNNING) {
> + this_cpu_write(nmi_state, NMI_LATCHED);
> + return;
> + }
> + this_cpu_write(nmi_state, NMI_EXECUTING);
> + this_cpu_write(nmi_cr2, read_cr2());
> +nmi_restart:
> +
Here if there are more than 2 NMIs nested, but the nmi_state is always
NMI_LATCHED.
>
> - /* On i386, may loop back to preprocess */
> - nmi_nesting_postprocess();
> + if (unlikely(this_cpu_read(nmi_cr2) != read_cr2()))
> + write_cr2(this_cpu_read(nmi_cr2));
> + if (this_cpu_dec_return(nmi_state))
> + goto nmi_restart;
> }
But here at most re-execute 2 NMIs, so some nmi lost ?
And cr2 is always the first NMI's cr2. CR2 is wrong for the later NMIs.
> void stop_nmi(void)
>
Thanks & Regards
Qixuan Wu.