linux-kernel - [PATCH v3 3/4] Add hwcap2 for x86

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Date:   Thu, 13 Oct 2016 16:02:24 +0200
From:   Grzegorz Andrejczuk <grzegorz.andrejczuk@...el.com>
To:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com, x86@...nel.org
Cc:     bp@...e.de, dave.hansen@...ux.intel.com,
        linux-kernel@...r.kernel.org, lukasz.daniluk@...el.com,
        james.h.cownie@...el.com, jacob.jun.pan@...el.com,
        Grzegorz Andrejczuk <grzegorz.andrejczuk@...el.com>
Subject: [PATCH v3 3/4] Add hwcap2 for x86

Add hwcap2 attribute for x86.
Reserve 1st bit of HWCAP2 for exposing Xeon Phi ring 3 monitor/mwait.
With this userspace apps can detect Ring 3 MONITOR/MWAIT instructions.

Signed-off-by: Grzegorz Andrejczuk <grzegorz.andrejczuk@...el.com>
---
 arch/x86/include/asm/elf.h        | 9 +++++++++
 arch/x86/include/uapi/asm/hwcap.h | 7 +++++++
 arch/x86/kernel/cpu/common.c      | 3 +++
 3 files changed, 19 insertions(+)
 create mode 100644 arch/x86/include/uapi/asm/hwcap.h

diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index e7f155c..0c4336f 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -258,6 +258,15 @@ extern int force_personality32;
 
 #define ELF_HWCAP		(boot_cpu_data.x86_capability[CPUID_1_EDX])
 
+extern unsigned int elf_hwcap2;
+
+/*
+ * HWCAP2 supplies kernel enabled CPU feature, so that the application
+ * can know that it can safely use them. The bits are defined in
+ * uapi/asm/hwcap.h.
+ */
+#define ELF_HWCAP2		elf_hwcap2
+
 /* This yields a string that ld.so will use to load implementation
    specific libraries for optimization.  This is more specific in
    intent than poking at uname or /proc/cpuinfo.
diff --git a/arch/x86/include/uapi/asm/hwcap.h b/arch/x86/include/uapi/asm/hwcap.h
new file mode 100644
index 0000000..d1f4f98
--- /dev/null
+++ b/arch/x86/include/uapi/asm/hwcap.h
@@ -0,0 +1,7 @@
+#ifndef _ASM_HWCAP_H
+#define _ASM_HWCAP_H 1
+
+/* Kernel enabled Ring 3 MWAIT for Xeon Phi*/
+#define HWCAP2_PHIR3MWAIT		(1 << 0)
+/* upto bit 31 free */
+#endif
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index bcc9ccc..ff26036 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -35,6 +35,7 @@
 #include <asm/desc.h>
 #include <asm/fpu/internal.h>
 #include <asm/mtrr.h>
+#include <asm/hwcap.h>
 #include <linux/numa.h>
 #include <asm/asm.h>
 #include <asm/bugs.h>
@@ -51,6 +52,8 @@
 
 #include "cpu.h"
 
+unsigned int elf_hwcap2 __read_mostly;
+
 /* all of these masks are initialized in setup_cpu_local_masks() */
 cpumask_var_t cpu_initialized_mask;
 cpumask_var_t cpu_callout_mask;
-- 
2.5.1