[PATCH 4.4 30/63] x86/mm: Add the nopcid boot option to turn off PCID

Greg Kroah-Hartman
2018-01-01T14:31:02Z

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>

---
Documentation/kernel-parameters.txt | 2 ++
arch/x86/kernel/cpu/common.c | 18 ++++++++++++++++++
2 files changed, 20 insertions(+)

--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2555,6 +2555,8 @@ bytes respectively. Such letter suffixes
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

--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -162,6 +162,24 @@ static int __init x86_mpx_setup(char *s)
}
__setup("nompx", x86_mpx_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 */