[PATCH v4 0/4] Enabling Ring 3 MONITOR/MWAIT feature for Knights Landing

[PATCH v4 0/4] Enabling Ring 3 MONITOR/MWAIT feature for Knights Landing

[Grzegorz Andrejczuk]

These patches enable Intel Xeon Phi x200 feature to use MONITOR/MWAIT
instruction in ring 3 (userspace) Patches set MSR 0x140 for all logical CPUs.
Then expose it as CPU feature and introduces elf HWCAP capability for x86.
Reference (the solution is temporary MSR definition will be in next SDM document):
https://software.intel.com/en-us/blogs/2016/10/06/intel-xeon-phi-product-family-x200-knl-user-mode-ring-3-monitor-and-mwait

v2:
Check MSR before wrmsrl
Shortened names
Used Word 3 for feature init_scattered_cpuid_features()
Fixed commit messages

v3:
Included Daves and Thomas comments

v4:
Wrapped the enabling code by CONFIG_X86_64
Add documentation for phir3mwait=disable cmdline switch
Move probe_ function call from early_intel_init to intel_init
Fixed commit messages


Grzegorz Andrejczuk (4):
  x86/phi: Add R3MWAIT register and bit to msr-info.h
  x86/phi: Add enabling of the R3MWAIT during boot
  x86: Use HWCAP2 to expoose Xeon Phi ring 3 MWAIT
  x86/phi: Add R3MWAIT to CPU features

 Documentation/kernel-parameters.txt |  5 +++++
 arch/x86/include/asm/cpufeatures.h  |  2 ++
 arch/x86/include/asm/elf.h          |  9 +++++++++
 arch/x86/include/asm/msr-index.h    |  5 +++++
 arch/x86/include/uapi/asm/hwcap2.h  |  7 +++++++
 arch/x86/kernel/cpu/common.c        |  3 +++
 arch/x86/kernel/cpu/intel.c         | 40 +++++++++++++++++++++++++++++++++++++
 7 files changed, 71 insertions(+)
 create mode 100644 arch/x86/include/uapi/asm/hwcap2.h

-- 
2.5.1

[PATCH v4 1/4] x86/phi: Add R3MWAIT register and bit to msr-info.h

[Grzegorz Andrejczuk]

Intel Xeon Phi x200 (codenamed Knights Landing) has MSR
MISC_THD_FEATURE_ENABLE 0x140.

Setting 2nd bit of this register makes MONITOR and MWAIT instructions
do not cause invalid-opcode exception when called from ring different
than 0.

Hex   Dec  Name                    Scope
140H  320  MISC_THD_FEATURE_ENABLE Thread
           0    Reserved
           1    if set to 1, the MONITOR and MWAIT instructions do not
                cause invalid-opcode exceptions when executed with CPL > 0
                or in virtual-8086 mode. If MWAIT is executed when CPL > 0
                or in virtual-8086 mode, and if EAX indicates a C-state
                other than C0 or C1, the instruction operates as if EAX
                indicated the C-state C1.
           63:2 Reserved

Signed-off-by: Grzegorz Andrejczuk <grzegorz.andrejczuk@intel.com>
---
 arch/x86/include/asm/msr-index.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 56f4c66..df9d8d3 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -540,6 +540,11 @@
 #define MSR_IA32_MISC_ENABLE_IP_PREF_DISABLE_BIT	39
 #define MSR_IA32_MISC_ENABLE_IP_PREF_DISABLE		(1ULL << MSR_IA32_MISC_ENABLE_IP_PREF_DISABLE_BIT)
 
+/* Intel Xeon Phi x200 ring 3 MONITOR/MWAIT */
+#define MSR_PHI_MISC_THD_FEATURE	0x00000140
+#define MSR_PHI_MISC_THD_FEATURE_R3MWAIT_BIT	1
+#define MSR_PHI_MISC_THD_FEATURE_R3MWAIT	(1ULL << MSR_PHI_MISC_THD_FEATURE_R3MWAIT_BIT)
+
 #define MSR_IA32_TSC_DEADLINE		0x000006E0
 
 /* P4/Xeon+ specific */
-- 
2.5.1

[PATCH v4 2/4] x86/phi: Add enabling of the R3MWAIT during boot

[Grzegorz Andrejczuk]

If processor is Intel Xeon Phi we enable user-level mwait feature.
Enabling this feature suppreses invalid-opcode error, when MONITOR/MWAIT
is called from ring 3.

Signed-off-by: Grzegorz Andrejczuk <grzegorz.andrejczuk@intel.com>
---
 Documentation/kernel-parameters.txt |  5 +++++
 arch/x86/kernel/cpu/intel.c         | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index a4f4d69..d58915b 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3120,6 +3120,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 	pg.		[PARIDE]
 			See Documentation/blockdev/paride.txt.
 
+	phir3mwait=	[X86] Disable Intel Xeon Phi x200 ring 3 MONITOR/MWAIT
+			feature for all cpus.
+			Format: { disable }
+			See arch/x86/kernel/cpu/intel.c
+
 	pirq=		[SMP,APIC] Manual mp-table setup
 			See Documentation/x86/i386/IO-APIC.txt.
 
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index fcd484d..1134dca 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -61,6 +61,39 @@ void check_mpx_erratum(struct cpuinfo_x86 *c)
 	}
 }
 
+#ifdef CONFIG_X86_64
+static int phi_r3mwait_disabled __read_mostly;
+
+static int __init phir3mwait_disable(char *__unused)
+{
+	phi_r3mwait_disabled = 1;
+	pr_warn("x86/phir3mwait: Disabled ring 3 MWAIT for Xeon Phi");
+	return 1;
+}
+__setup("phir3mwait=disable", phir3mwait_disable);
+
+static void probe_xeon_phi_r3mwait(struct cpuinfo_x86 *c)
+{
+	if (phi_r3mwait_disabled)
+		return;
+
+	/*
+	* Setting ring 3 MONITOR/MWAIT for thread
+	* when CPU is Xeon Phi Family x200.
+	*/
+	if (c->x86 == 6 && c->x86_model == INTEL_FAM6_XEON_PHI_KNL) {
+		u64 msr;
+
+		rdmsrl(MSR_PHI_MISC_THD_FEATURE, msr);
+		msr |= MSR_PHI_MISC_THD_FEATURE_R3MWAIT;
+		wrmsrl(MSR_PHI_MISC_THD_FEATURE, msr);
+	}
+}
+
+#else
+static void probe_xeon_phi_r3mwait(struct cpuinfo_x86 *__unused) {}
+#endif
+
 static void early_init_intel(struct cpuinfo_x86 *c)
 {
 	u64 misc_enable;
@@ -565,6 +598,8 @@ static void init_intel(struct cpuinfo_x86 *c)
 		detect_vmx_virtcap(c);
 
 	init_intel_energy_perf(c);
+
+	probe_xeon_phi_r3mwait(c);
 }
 
 #ifdef CONFIG_X86_32
-- 
2.5.1

[PATCH v4 3/4] x86: Use HWCAP2 to expoose Xeon Phi ring 3 MWAIT

[Grzegorz Andrejczuk]

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

[PATCH v4 4/4] x86/phi: Add R3MWAIT to CPU features

[Grzegorz Andrejczuk]

Add cpu feature for ring 3 monitor/mwait.
Set HWCAP2 1st bit during init.

Signed-off-by: Grzegorz Andrejczuk <grzegorz.andrejczuk@intel.com>
---
 arch/x86/include/asm/cpufeatures.h | 2 ++
 arch/x86/kernel/cpu/intel.c        | 4 ++++
 2 files changed, 6 insertions(+)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 92a8308..d430200 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -71,6 +71,8 @@
 #define X86_FEATURE_RECOVERY	( 2*32+ 0) /* CPU in recovery mode */
 #define X86_FEATURE_LONGRUN	( 2*32+ 1) /* Longrun power control */
 #define X86_FEATURE_LRTI	( 2*32+ 3) /* LongRun table interface */
+/* Xeon Phi x200 ring 3 MONITOR/MWAIT enabled */
+#define X86_FEATURE_PHIR3MWAIT	( 2*32+ 4)
 
 /* Other features, Linux-defined mapping, word 3 */
 /* This range is used for feature bits which conflict or are synthesized */
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 1134dca..a2ea905 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -14,6 +14,8 @@
 #include <asm/bugs.h>
 #include <asm/cpu.h>
 #include <asm/intel-family.h>
+#include <asm/hwcap2.h>
+#include <asm/elf.h>
 
 #ifdef CONFIG_X86_64
 #include <linux/topology.h>
@@ -87,6 +89,8 @@ static void probe_xeon_phi_r3mwait(struct cpuinfo_x86 *c)
 		rdmsrl(MSR_PHI_MISC_THD_FEATURE, msr);
 		msr |= MSR_PHI_MISC_THD_FEATURE_R3MWAIT;
 		wrmsrl(MSR_PHI_MISC_THD_FEATURE, msr);
+		set_cpu_cap(c, X86_FEATURE_PHIR3MWAIT);
+		ELF_HWCAP2 |= HWCAP2_PHIR3MWAIT;
 	}
 }
 
-- 
2.5.1

Re: [PATCH v4 2/4] x86/phi: Add enabling of the R3MWAIT during boot

[Thomas Gleixner]

On Tue, 18 Oct 2016, Grzegorz Andrejczuk wrote:
> +static void probe_xeon_phi_r3mwait(struct cpuinfo_x86 *c)
> +{
> +	if (phi_r3mwait_disabled)
> +		return;

So you return when the command line option to disable the feature was
given. That's not really a good choice if the feature is already enabled
due to BIOS featuritis. This can also happen when you kexec from a enabled
kernel into one which has the command line option set.

You really should make sure that the command line option results in
disabling the feature no matter what.

Thanks,

	tglx

Re: [PATCH v4 3/4] x86: Use HWCAP2 to expoose Xeon Phi ring 3 MWAIT

[Thomas Gleixner]

On Tue, 18 Oct 2016, Grzegorz Andrejczuk wrote:

x86: Use HWCAP2 to expoose Xeon Phi ring 3 MWAIT

expoose ? Please proof read your patches before posting.

Thanks,

	tglx

Re: [PATCH v4 4/4] x86/phi: Add R3MWAIT to CPU features

[Thomas Gleixner]

On Tue, 18 Oct 2016, Grzegorz Andrejczuk wrote:

x86/phi: is not a proper subsystem. x86/cpufeature: is what you want here.

Thanks,

	tglx