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Date:   Fri, 7 Jun 2019 10:52:59 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Nadav Amit <namit@vmware.com>
Cc:     the arch/x86 maintainers <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Andy Lutomirski <luto@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Jason Baron <jbaron@akamai.com>, Jiri Kosina <jkosina@suse.cz>,
        David Laight <David.Laight@ACULAB.COM>,
        Borislav Petkov <bp@alien8.de>,
        Julia Cartwright <julia@ni.com>, Jessica Yu <jeyu@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Edward Cree <ecree@solarflare.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH 12/15] x86/static_call: Add out-of-line static call
 implementation
Message-ID: <20190607085259.GE3463@hirez.programming.kicks-ass.net>
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On Fri, Jun 07, 2019 at 10:38:46AM +0200, Peter Zijlstra wrote:
> On Fri, Jun 07, 2019 at 06:13:58AM +0000, Nadav Amit wrote:
> > > On Jun 5, 2019, at 6:08 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > > +void arch_static_call_transform(void *site, void *tramp, void *func)
> > > +{
> > > +	unsigned char opcodes[CALL_INSN_SIZE];
> > > +	unsigned char insn_opcode;
> > > +	unsigned long insn;
> > > +	s32 dest_relative;
> > > +
> > > +	mutex_lock(&text_mutex);
> > > +
> > > +	insn = (unsigned long)tramp;
> > > +
> > > +	insn_opcode = *(unsigned char *)insn;
> > > +	if (insn_opcode != 0xE9) {
> > > +		WARN_ONCE(1, "unexpected static call insn opcode 0x%x at %pS",
> > > +			  insn_opcode, (void *)insn);
> > > +		goto unlock;
> > 
> > This might happen if a kprobe is installed on the call, no?
> > 
> > I don’t know if you want to be more gentle handling of this case (or perhaps
> > modify can_probe() to prevent such a case).
> > 
> 
> yuck.. yes, that's something that needs consideration.

For jump_label this is avoided by jump_label_text_reserved(), I'm
thinking static_call should do the same.