linux-kernel - Re: [PATCH 20/24] objtool: Another static block fail

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Message-ID: <20180131100119.GJ2269@hirez.programming.kicks-ass.net>
Date:   Wed, 31 Jan 2018 11:01:19 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Jason Baron <jbaron@...mai.com>
Subject: Re: [PATCH 20/24] objtool: Another static block fail

On Tue, Jan 30, 2018 at 09:12:21PM -0600, Josh Poimboeuf wrote:
> 
> Or, maybe we should just forget the whole thing and just stick with the
> dynamic IBRS checks with lfence.  Yes, it's less ideal for the kernel,
> but adding these acrobatics to objtool also has a cost.

For now, IBRS seems off the table entirely. But no, I really don't want
to have to unconditionally eat the LFENCE cost in all those sites.