linux-kernel - Re: [PATCH] x86/paravirt: Remove 'noreplace-paravirt' cmdline option

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Message-ID: <449d9ac6-2313-86f3-2f39-a5c1e00fd339@suse.com>
Date:   Wed, 31 Jan 2018 06:59:01 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        Alok Kataria <akataria@...are.com>,
        Rusty Russell <rusty@...tcorp.com.au>
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>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] x86/paravirt: Remove 'noreplace-paravirt' cmdline option

On 31/01/18 05:13, Josh Poimboeuf wrote:
> The 'noreplace-paravirt' option disables paravirt patching, leaving the
> original pv indirect calls in place.
> 
> That's highly incompatible with retpolines, unless we want to uglify
> paravirt even further and convert the paravirt calls to retpolines.
> 
> As far as I can tell, the option doesn't seem to be useful for much
> other than introducing surprising corner cases and making the kernel
> vulnerable to Spectre v2.  It was probably a debug option from the early
> paravirt days.  So just remove it.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen