linux-kernel - Re: 4.14.9 with CONFIG

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Date:   Fri, 29 Dec 2017 12:34:42 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Alexander Tsoy <alexander@...y.me>
Cc:     Dave Hansen <dave.hansen@...el.com>, Greg KH <greg@...ah.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...e.de>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Borislav Petkov <bp@...en8.de>,
        Borislav Petkov <bpetkov@...e.de>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...hat.com>,
        Will Deacon <will.deacon@....com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        Hugh Dickins <hughd@...gle.com>,
        Kees Cook <keescook@...gle.com>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: 4.14.9 with CONFIG_MCORE2 fails to boot

On Fri, Dec 29, 2017 at 12:22 PM, Alexander Tsoy <alexander@...y.me> wrote:
>> But double-checking that "-march=core2" case is definitely worth
>> looking into. Especially since there are clear indications that it's
>> gcc version-dependent anyway. Alexander?
>
> Yes, the change suggested by Dave makes the problem go away.

Ok, that's good information.

It doesn't really explain *why* that commit 7f2590a110b8
("x86/entry/64: Use a per-CPU trampoline stack for IDT entries") ends
up being sensitive to that compiler option, though.

So it narrows the cause down, but it doesn't really root-cause the
problem. It tends to be almost impossible to find differences in code
generation, because they are generally all over.

Ho humm. What happens if you change the "-march=core2" to
"-mtune=core2"? Does it still boot?

Because maybe the actual differences that "-march=core2" generates
might be easier to see when compared to "-mtune=core2".

                  Linus