Date: Thu, 23 Jul 2015 14:12:47 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: Jason Baron <jasonbaron0@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@amacapital.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Mikulas Patocka <mpatocka@redhat.com>,
        Paul Mackerras <paulus@samba.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Vince Weaver <vince@deater.net>, "hillf.zj" <hillf.zj@alibaba-inc.com>,
        Valdis Kletnieks <Valdis.Kletnieks@vt.edu>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: Kernel broken on processors without performance counters
Message-ID: <20150723141247.32d760eb@gandalf.local.home>
In-Reply-To: <55B12570.4070709@gmail.com>
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On Thu, 23 Jul 2015 13:33:36 -0400
Jason Baron <jasonbaron0@gmail.com> wrote:

> On 07/23/2015 01:08 PM, Peter Zijlstra wrote:
> > On Thu, Jul 23, 2015 at 11:34:50AM -0400, Steven Rostedt wrote:
> >> On Thu, 23 Jul 2015 12:42:15 +0200
> >> Peter Zijlstra <peterz@infradead.org> wrote:
> >>
> >>> static __always_inline bool arch_static_branch_jump(struct static_key *key, bool inv)
> >>> {
> >>> 	if (!inv) {
> >>> 		asm_volatile_goto("1:"
> >>> 			"jmp %l[l_yes]\n\t"
> >> And what happens when this gets converted to a two byte jump?
> >>
> > That would be bad, how can we force it to emit 5 bytes?
> hmm....I don't think that's an issue, the patching code can
> detect if its a 2-byte jump - 0xeb, or 5-byte: 0xe9, and do
> the correct no-op. Same going the other way. See the code
> I posted a few mails back. In fact, this gets us to the
> smaller 2-byte no-ops in cases where we are initialized
> to jump.
>

Ah right, and I already have the code that checks that (from the
original plan).

-- Steve
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