[PATCH 4.1 19/65] x86/mm: Add the 'nopcid' boot option to turn off PCID

[Pavel Tatashin <pasha.tatashin@oracle.com>]

From: Andy Lutomirski <luto@kernel.org>

commit 0790c9aad84901ca1bdc14746175549c8b5da215 upstream.

The parameter is only present on x86_64 systems to save a few bytes,
as PCID is always disabled on x86_32.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Nadav Amit <nadav.amit@gmail.com>
Reviewed-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/8bbb2e65bcd249a5f18bfb8128b4689f08ac2b60.1498751203.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

(cherry picked from commit dcccd3c266e24ce80ecf592765315c54c222ac33)
Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
---
 Documentation/kernel-parameters.txt |  2 ++
 arch/x86/kernel/cpu/common.c        | 18 ++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index ceaab09a279e..97bc24101896 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2471,6 +2471,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 	nopat		[X86] Disable PAT (page attribute table extension of
 			pagetables) support.
 
+	nopcid		[X86-64] Disable the PCID cpu feature.
+
 	norandmaps	Don't use address space randomization.  Equivalent to
 			echo 0 > /proc/sys/kernel/randomize_va_space
 
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 90ef802d9d90..843be1de5ddb 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -172,6 +172,24 @@ static int __init x86_xsaves_setup(char *s)
 }
 __setup("noxsaves", x86_xsaves_setup);
 
+#ifdef CONFIG_X86_64
+static int __init x86_pcid_setup(char *s)
+{
+	/* require an exact match without trailing characters */
+	if (strlen(s))
+		return 0;
+
+	/* do not emit a message if the feature is not present */
+	if (!boot_cpu_has(X86_FEATURE_PCID))
+		return 1;
+
+	setup_clear_cpu_cap(X86_FEATURE_PCID);
+	pr_info("nopcid: PCID feature disabled\n");
+	return 1;
+}
+__setup("nopcid", x86_pcid_setup);
+#endif
+
 static int __init x86_noinvpcid_setup(char *s)
 {
 	/* noinvpcid doesn't accept parameters */
-- 
2.16.2