Message-ID: <1514584257.28262.13.camel@tsoy.me>
Subject: Re: 4.14.9 with CONFIG_MCORE2 fails to boot
From: Alexander Tsoy <alexander@tsoy.me>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Hansen <dave.hansen@intel.com>, Greg KH <greg@kroah.com>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
        Borislav Petkov <bp@suse.de>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Borislav Petkov <bp@alien8.de>, Borislav Petkov <bpetkov@suse.de>,
        Brian Gerst <brgerst@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        David Laight <David.Laight@aculab.com>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        Eduardo Valentin <eduval@amazon.com>,
        Greg KH <gregkh@linuxfoundation.org>, "H. Peter Anvin" <hpa@zytor.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>, Juergen Gross <jgross@suse.com>,
        Peter Zijlstra <peterz@infradead.org>, Rik van Riel <riel@redhat.com>,
        Will Deacon <will.deacon@arm.com>,
        "Liguori, Anthony" <aliguori@amazon.com>,
        Daniel Gruss <daniel.gruss@iaik.tugraz.at>,
        Hugh Dickins <hughd@google.com>, Kees Cook <keescook@google.com>,
        Kernel Mailing List <linux-kernel@vger.kernel.org>,
        stable <stable@vger.kernel.org>
Date: Sat, 30 Dec 2017 00:50:57 +0300
In-Reply-To: <CA+55aFxEQm2DCUFZ4aS=EEsk9uBSDwZo0ExFsQjPRcHcX-R5kw@mail.gmail.com>
References: <1514453602.6251.8.camel@tsoy.me>
         <20171229091741.GC18441@kroah.com> <1514557888.28262.1.camel@tsoy.me>
         <1514558513.28262.3.camel@tsoy.me>
         <1b4569ee-8c06-4480-447b-2af8f6804053@intel.com>
         <CA+55aFwgNQt_7C20XjgKt3MNnrix3wJcVou5GGNX3yRvMMtP4g@mail.gmail.com>
         <1514578936.28262.11.camel@tsoy.me>
         <CA+55aFxEQm2DCUFZ4aS=EEsk9uBSDwZo0ExFsQjPRcHcX-R5kw@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1896
Lines: 45

В Пт, 29/12/2017 в 12:34 -0800, Linus Torvalds пишет:
> On Fri, Dec 29, 2017 at 12:22 PM, Alexander Tsoy <alexander@tsoy.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".

That's interesting. Compiled with -mtune=core2, the kernel fails to
boot.

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 3e73bc255e4e..f4d8f9497666 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -127,8 +127,7 @@ else
         cflags-$(CONFIG_MK8) += $(call cc-option,-march=k8)
         cflags-$(CONFIG_MPSC) += $(call cc-option,-march=nocona)
 
-        cflags-$(CONFIG_MCORE2) += \
-                $(call cc-option,-march=core2,$(call cc-option,-
mtune=generic))
+        cflags-$(CONFIG_MCORE2) += $(call cc-option,-mtune=core2)
    cflags-$(CONFIG_MATOM) += $(call cc-option,-march=atom) \
        $(call cc-option,-mtune=atom,$(call cc-option,-mtune=generic))
         cflags-$(CONFIG_GENERIC_CPU) += $(call cc-option,-
mtune=generic)