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Subject: Re: [PATCH] x86/paravirt: Remove 'noreplace-paravirt' cmdline option
To: Josh Poimboeuf <jpoimboe@redhat.com>, x86@kernel.org,
 Alok Kataria <akataria@vmware.com>, Rusty Russell <rusty@rustcorp.com.au>
Cc: David Woodhouse <dwmw2@infradead.org>,
 Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
 Dave Hansen <dave.hansen@intel.com>, Ashok Raj <ashok.raj@intel.com>,
 Tim Chen <tim.c.chen@linux.intel.com>, Andy Lutomirski <luto@kernel.org>,
 Linus Torvalds <torvalds@linux-foundation.org>,
 Greg KH <gregkh@linuxfoundation.org>, Andrea Arcangeli
 <aarcange@redhat.com>, Andi Kleen <ak@linux.intel.com>,
 Arjan Van De Ven <arjan.van.de.ven@intel.com>,
 Dan Williams <dan.j.williams@intel.com>, Paolo Bonzini
 <pbonzini@redhat.com>, Jun Nakajima <jun.nakajima@intel.com>,
 Asit Mallick <asit.k.mallick@intel.com>, Jason Baron <jbaron@akamai.com>,
 Peter Zijlstra <peterz@infradead.org>
References: <20180123152539.374360046@infradead.org>
 <20180123152638.162540737@infradead.org>
 <20180129183850.b6mjtuz4j5d7wum6@treble>
 <20180129192108.GR2249@hirez.programming.kicks-ass.net>
 <20180130160237.nimxrlykl4ttsfuk@treble>
 <20180131041333.2x6blhxirc2kclrq@treble>
From: Juergen Gross <jgross@suse.com>
Message-ID: <449d9ac6-2313-86f3-2f39-a5c1e00fd339@suse.com>
Date: Wed, 31 Jan 2018 06:59:01 +0100
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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@redhat.com>

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


Juergen