[PATCH 25/26] x86, pkeys: actually enable Memory Protection Keys in CPU

[Dave Hansen]

This sets the bit in 'cr4' to actually enable the protection
keys feature.  We also include a boot-time disable for the
feature "nopku".

Seting X86_CR4_PKE will cause the X86_FEATURE_OSPKE cpuid
bit to appear set.  At this point in boot, identify_cpu()
has already run the actual CPUID instructions and populated
the "cpu features" structures.  We need to go back and
re-run identify_cpu() to make sure it gets updated values.

We *could* simply re-populate the 11th word of the cpuid
data, but this is probably quick enough.

Also note that with the cpu_has() check and X86_FEATURE_PKU
present in disabled-features.h, we do not need an #ifdef
for setup_pku().

---

 b/Documentation/kernel-parameters.txt |    3 +++
 b/arch/x86/kernel/cpu/common.c        |   26 ++++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff -puN arch/x86/kernel/cpu/common.c~pkeys-50-should-be-last-patch arch/x86/kernel/cpu/common.c
--- a/arch/x86/kernel/cpu/common.c~pkeys-50-should-be-last-patch	2015-09-16 09:45:55.420471313 -0700
+++ b/arch/x86/kernel/cpu/common.c	2015-09-16 09:45:55.426471585 -0700
@@ -289,6 +289,31 @@ static __always_inline void setup_smap(s
 }
 
 /*
+ * Protection Keys are not available in 32-bit mode.
+ */
+static __always_inline void setup_pku(struct cpuinfo_x86 *c)
+{
+	if (!cpu_has(c, X86_FEATURE_PKU))
+		return;
+
+	cr4_set_bits(X86_CR4_PKE);
+	/*
+	 * Seting X86_CR4_PKE will cause the X86_FEATURE_OSPKE
+	 * cpuid bit to be set.  We need to ensure that we
+	 * update that bit in this CPU's "cpu_info".
+	 */
+	get_cpu_cap(c);
+}
+#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
+static __init int setup_disable_pku(char *arg)
+{
+	setup_clear_cpu_cap(X86_FEATURE_PKU);
+	return 1;
+}
+__setup("nopku", setup_disable_pku);
+#endif /* CONFIG_X86_64 */
+
+/*
  * Some CPU features depend on higher CPUID levels, which may not always
  * be available due to CPUID level capping or broken virtualization
  * software.  Add those features to this table to auto-disable them.
@@ -947,6 +972,7 @@ static void identify_cpu(struct cpuinfo_
 	init_hypervisor(c);
 	x86_init_rdrand(c);
 	x86_init_cache_qos(c);
+	setup_pku(c);
 
 	/*
 	 * Clear/Set all flags overriden by options, need do it
diff -puN Documentation/kernel-parameters.txt~pkeys-50-should-be-last-patch Documentation/kernel-parameters.txt
--- a/Documentation/kernel-parameters.txt~pkeys-50-should-be-last-patch	2015-09-16 09:45:55.422471404 -0700
+++ b/Documentation/kernel-parameters.txt	2015-09-16 09:45:55.427471630 -0700
@@ -955,6 +955,9 @@ bytes respectively. Such letter suffixes
 			See Documentation/x86/intel_mpx.txt for more
 			information about the feature.
 
+	nopku		[X86] Disable Memory Protection Keys CPU feature found
+			in some Intel CPUs.
+
 	eagerfpu=	[X86]
 			on	enable eager fpu restore
 			off	disable eager fpu restore
_
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