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[PATCH v3 09/11] x86/mm: Add nopcid to turn off PCID

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  [PATCH v3 09/11] x86/mm: Add nopcid to turn off PCID Andy Lutomirski <luto@kernel.org> - 2017-06-21 07:30 +0200
    Re: [PATCH v3 09/11] x86/mm: Add nopcid to turn off PCID Thomas Gleixner <tglx@linutronix.de> - 2017-06-21 11:30 +0200
    Re: [PATCH v3 09/11] x86/mm: Add nopcid to turn off PCID Borislav Petkov <bp@alien8.de> - 2017-06-23 11:40 +0200

#1671347 — [PATCH v3 09/11] x86/mm: Add nopcid to turn off PCID

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

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 0f5c3b4347c6..aa385109ae58 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2648,6 +2648,8 @@
 	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 c8b39870f33e..904485e7b230 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -168,6 +168,24 @@ 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 */
-- 
2.9.4

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#1671532

On Tue, 20 Jun 2017, Andy Lutomirski wrote:

> 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: Thomas Gleixner <tglx@linutronix.de>

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#1673440

On Tue, Jun 20, 2017 at 10:22:15PM -0700, Andy Lutomirski wrote:
> 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>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  2 ++
>  arch/x86/kernel/cpu/common.c                    | 18 ++++++++++++++++++
>  2 files changed, 20 insertions(+)

Reviewed-by: Borislav Petkov <bp@suse.de>

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

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