linux-kernel - Re: [PATCH 3/4] x86/ftrace: make ftrace_int3

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Message-ID: <20190430004504.GH31379@linux.intel.com>
Date:   Mon, 29 Apr 2019 17:45:04 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andrew Lutomirski <luto@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Nicolai Stange <nstange@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Juergen Gross <jgross@...e.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Joerg Roedel <jroedel@...e.de>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        live-patching@...r.kernel.org,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH 3/4] x86/ftrace: make ftrace_int3_handler() not to skip
 fops invocation

On Mon, Apr 29, 2019 at 05:08:46PM -0700, Sean Christopherson wrote:
> On Mon, Apr 29, 2019 at 03:22:09PM -0700, Linus Torvalds wrote:
> > On Mon, Apr 29, 2019 at 3:08 PM Sean Christopherson
> > <sean.j.christopherson@...el.com> wrote:
> > >
> > > FWIW, Lakemont (Quark) doesn't block NMI/SMI in the STI shadow, but I'm
> > > not sure that counters the "horrible errata" statement ;-).  SMI+RSM saves
> > > and restores STI blocking in that case, but AFAICT NMI has no such
> > > protection and will effectively break the shadow on its IRET.
> > 
> > Ugh. I can't say I care deeply about Quark (ie never seemed to go
> > anywhere), but it's odd. I thought it was based on a Pentium core (or
> > i486+?). Are you saying those didn't do it either?
> 
> It's 486 based, but either way I suspect the answer is "yes".  IIRC,
> Knights Corner, a.k.a. Larrabee, also had funkiness around SMM and that
> was based on P54C, though I'm struggling to recall exactly what the
> Larrabee weirdness was.

Aha!  Found an ancient comment that explicitly states P5 does not block
NMI/SMI in the STI shadow, while P6 does block NMI/SMI.