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[PATCH v7 2/4] x86: Use HWCAP2 to expose Xeon Phi ring 3 MWAIT

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  [PATCH v7 2/4] x86: Use HWCAP2 to expose Xeon Phi ring 3 MWAIT Grzegorz Andrejczuk <grzegorz.andrejczuk@intel.com> - 2016-10-28 16:00 +0200
    Re: [PATCH v7 2/4] x86: Use HWCAP2 to expose Xeon Phi ring 3 MWAIT Thomas Gleixner <tglx@linutronix.de> - 2016-10-31 02:20 +0100

#1511144 — [PATCH v7 2/4] x86: Use HWCAP2 to expose Xeon Phi ring 3 MWAIT

Add HWCAP2 for x86 and reserve its 1st bit to expose
Xeon Phi ring 3 monitor/mwait to userspace apps.

Signed-off-by: Grzegorz Andrejczuk <grzegorz.andrejczuk@intel.com>
---
 arch/x86/include/asm/elf.h         | 9 +++++++++
 arch/x86/include/uapi/asm/hwcap2.h | 7 +++++++
 arch/x86/kernel/cpu/common.c       | 3 +++
 3 files changed, 19 insertions(+)
 create mode 100644 arch/x86/include/uapi/asm/hwcap2.h

diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index e7f155c..59703aa 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 mask with kernel enabled CPU features, so that
+ * the application can discover that it can safely use them.
+ * The bits are defined in uapi/asm/hwcap2.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/hwcap2.h b/arch/x86/include/uapi/asm/hwcap2.h
new file mode 100644
index 0000000..90ef445
--- /dev/null
+++ b/arch/x86/include/uapi/asm/hwcap2.h
@@ -0,0 +1,7 @@
+#ifndef _ASM_HWCAP2_H
+#define _ASM_HWCAP2_H
+
+/* Kernel enabled Ring 3 MWAIT for Xeon Phi*/
+#define HWCAP2_PHIR3MWAIT		(1 << 0)
+
+#endif
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index bcc9ccc..fdbf708 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/hwcap2.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

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#1512252

On Fri, 28 Oct 2016, Grzegorz Andrejczuk wrote:

The subject subsystem wants to be 'x86/elf:'

And please remove that Xeon PHI reference. See below.

> Add HWCAP2 for x86 and reserve its 1st bit to expose

s/1st bit/bit 0/ please

> +
> +/* Kernel enabled Ring 3 MWAIT for Xeon Phi*/
> +#define HWCAP2_PHIR3MWAIT		(1 << 0)

Can we please make that

/* MWAIT/MONITOR are available in ring 3 */
#define HWCAP2_RING3MWAIT		(1 << 0)

Simply because this feature might become available on other platforms and
then the PHI thing does not make any sense. We do not care on which CPU
model this works, we care about the fact that it works.

Thanks,

	tglx

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