linux-kernel - [tip:x86/pti] x86/paravirt: Remove 'noreplace-paravirt' cmdline option

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Date:   Wed, 31 Jan 2018 01:42:53 -0800
From:   tip-bot for Josh Poimboeuf <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     torvalds@...ux-foundation.org, jun.nakajima@...el.com,
        pbonzini@...hat.com, tglx@...utronix.de, jbaron@...mai.com,
        mingo@...nel.org, asit.k.mallick@...el.com,
        gregkh@...uxfoundation.org, tim.c.chen@...ux.intel.com,
        arjan.van.de.ven@...el.com, linux-kernel@...r.kernel.org,
        jpoimboe@...hat.com, dan.j.williams@...el.com, hpa@...or.com,
        dave.hansen@...el.com, rusty@...tcorp.com.au, jgross@...e.com,
        akataria@...are.com, ashok.raj@...el.com, aarcange@...hat.com,
        ak@...ux.intel.com, luto@...nel.org, dwmw2@...radead.org,
        peterz@...radead.org
Subject: [tip:x86/pti] x86/paravirt: Remove 'noreplace-paravirt' cmdline
 option

Commit-ID:  12c69f1e94c89d40696e83804dd2f0965b5250cd
Gitweb:     https://git.kernel.org/tip/12c69f1e94c89d40696e83804dd2f0965b5250cd
Author:     Josh Poimboeuf <jpoimboe@...hat.com>
AuthorDate: Tue, 30 Jan 2018 22:13:33 -0600
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Wed, 31 Jan 2018 10:37:45 +0100

x86/paravirt: Remove 'noreplace-paravirt' cmdline option

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>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Juergen Gross <jgross@...e.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Ashok Raj <ashok.raj@...el.com>
Cc: Greg KH <gregkh@...uxfoundation.org>
Cc: Jun Nakajima <jun.nakajima@...el.com>
Cc: Tim Chen <tim.c.chen@...ux.intel.com>
Cc: Rusty Russell <rusty@...tcorp.com.au>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Asit Mallick <asit.k.mallick@...el.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Jason Baron <jbaron@...mai.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Alok Kataria <akataria@...are.com>
Cc: Arjan Van De Ven <arjan.van.de.ven@...el.com>
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: Dan Williams <dan.j.williams@...el.com>
Link: https://lkml.kernel.org/r/20180131041333.2x6blhxirc2kclrq@treble

---
 Documentation/admin-guide/kernel-parameters.txt |  2 --
 arch/x86/kernel/alternative.c                   | 14 --------------
 2 files changed, 16 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 46b26bf..1e762c2 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2742,8 +2742,6 @@
 	norandmaps	Don't use address space randomization.  Equivalent to
 			echo 0 > /proc/sys/kernel/randomize_va_space
 
-	noreplace-paravirt	[X86,IA-64,PV_OPS] Don't patch paravirt_ops
-
 	noreplace-smp	[X86-32,SMP] Don't replace SMP instructions
 			with UP alternatives
 
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 30571fd..a481763 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -46,17 +46,6 @@ static int __init setup_noreplace_smp(char *str)
 }
 __setup("noreplace-smp", setup_noreplace_smp);
 
-#ifdef CONFIG_PARAVIRT
-static int __initdata_or_module noreplace_paravirt = 0;
-
-static int __init setup_noreplace_paravirt(char *str)
-{
-	noreplace_paravirt = 1;
-	return 1;
-}
-__setup("noreplace-paravirt", setup_noreplace_paravirt);
-#endif
-
 #define DPRINTK(fmt, args...)						\
 do {									\
 	if (debug_alternative)						\
@@ -599,9 +588,6 @@ void __init_or_module apply_paravirt(struct paravirt_patch_site *start,
 	struct paravirt_patch_site *p;
 	char insnbuf[MAX_PATCH_LEN];
 
-	if (noreplace_paravirt)
-		return;
-
 	for (p = start; p < end; p++) {
 		unsigned int used;