linux-kernel - Re: [PATCH] x86/idt: load idt early in start

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Message-ID: <736042713.31089814.1511845056722.JavaMail.zimbra@redhat.com>
Date:   Mon, 27 Nov 2017 23:57:36 -0500 (EST)
From:   Chunyu Hu <chuhu@...hat.com>
To:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Ingo Molnar <mingo@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/idt: load idt early in start_secondary



----- Original Message -----
> From: "Andy Lutomirski" <luto@...nel.org>
> To: "Chunyu Hu" <chuhu@...hat.com>
> Cc: "Thomas Gleixner" <tglx@...utronix.de>, "Ingo Molnar" <mingo@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
> "Peter Zijlstra" <peterz@...radead.org>, "Andrew Lutomirski" <luto@...nel.org>, "Borislav Petkov" <bp@...en8.de>,
> "Steven Rostedt" <rostedt@...dmis.org>, linux-kernel@...r.kernel.org
> Sent: Tuesday, November 28, 2017 11:41:20 AM
> Subject: Re: [PATCH] x86/idt: load idt early in start_secondary
> 
> On Mon, Nov 27, 2017 at 6:21 AM, Chunyu Hu <chuhu@...hat.com> wrote:
> > For ap, idt is first loaded in cpu_init() with load_current_idt(),
> > that is to say, no exception can be handled before there. And then
> > the idt_table has been completed by the bp.
> >
> > While there are some WARNs which needs the UD exception handling
> > in the early boot code might be triggered when something uexpected
> > happens during boot. In that case, cpu would fail to boot as the
> > exception can't be handled. A WARNing during boot is not usually
> > meaning the system could not boot.
> >
> > One use case is when ftrace=function is setup in kernel cmdline, the
> > ftrace callback function will be called for every traced function.
> > And in my case, the first traced function is load_ucode_ap. And there
> > are WARN()s in function trace callback handling, it failed to reboot
> > as one of the WARN()s is triggered before load_current_idt() executed.
> >
> > To make WARN()s can work earlier to ap, we load the idt_table early
> > in start_secondary, and keep the second time idt load in cpu_init,
> > as there is a load_ucode_ap() there.
> 
> Reviewed-by: Andy Lutomirski <luto@...nel.org>
> 
> Except that this is presumably missing a Cc: stable.

Do I need to resend this origin version and Cc stable?

> 

-- 
Regards,
Chunyu Hu