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

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Date:   Tue, 30 Jan 2018 22:13:33 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org, Juergen Gross <jgross@...e.com>,
        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: [PATCH] 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>
---
 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 a205567f537f..f6741a5d89e7 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2739,8 +2739,6 @@
 	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 30571fdaaf6f..a481763a3776 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;
 
-- 
2.14.3