linux-kernel - [PATCH 3.16 01/63] x86/fpu: Fix the 'nofxsr' boot parameter to also clear X86_FEATURE_FXSR

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Date:   Sat, 22 Sep 2018 01:15:42 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Ingo Molnar" <mingo@...nel.org>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Borislav Petkov" <bp@...en8.de>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Fenghua Yu" <fenghua.yu@...el.com>,
        "Oleg Nesterov" <oleg@...hat.com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Andy Lutomirski" <luto@...capital.net>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>
Subject: [PATCH 3.16 01/63] x86/fpu: Fix the 'nofxsr' boot parameter to
 also clear X86_FEATURE_FXSR_OPT

3.16.58-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ingo Molnar <mingo@...nel.org>

commit d364a7656c1855c940dfa4baf4ebcc3c6a9e6fd2 upstream.

I tried to simulate an ancient CPU via this option, and
found that it still has fxsr_opt enabled, confusing the
FPU code.

Make the 'nofxsr' option also clear FXSR_OPT flag.

Cc: Andy Lutomirski <luto@...capital.net>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/kernel/cpu/common.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -199,6 +199,15 @@ static int __init x86_noinvpcid_setup(ch
 }
 early_param("noinvpcid", x86_noinvpcid_setup);
 
+static int __init x86_fxsr_setup(char *s)
+{
+	setup_clear_cpu_cap(X86_FEATURE_FXSR);
+	setup_clear_cpu_cap(X86_FEATURE_FXSR_OPT);
+	setup_clear_cpu_cap(X86_FEATURE_XMM);
+	return 1;
+}
+__setup("nofxsr", x86_fxsr_setup);
+
 #ifdef CONFIG_X86_32
 static int cachesize_override = -1;
 static int disable_x86_serial_nr = 1;
@@ -210,14 +219,6 @@ static int __init cachesize_setup(char *
 }
 __setup("cachesize=", cachesize_setup);
 
-static int __init x86_fxsr_setup(char *s)
-{
-	setup_clear_cpu_cap(X86_FEATURE_FXSR);
-	setup_clear_cpu_cap(X86_FEATURE_XMM);
-	return 1;
-}
-__setup("nofxsr", x86_fxsr_setup);
-
 static int __init x86_sep_setup(char *s)
 {
 	setup_clear_cpu_cap(X86_FEATURE_SEP);