[PATCH v8: 0/4] Enabling Ring 3 MONITOR/MWAIT feature for Knights Landing

[PATCH v8: 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:
https://software.intel.com/en-us/blogs/2016/10/06/intel-xeon-phi-product-family-x200-knl-user-mode-ring-3-monitor-and-mwait

v8:
Fixed commit messages
Removed logging
Used msr_set/clear_bit functions instesd of wrmsrl
Fixed documentation
Renamed HWCAP2_PHIR3MWAIT to HWCAP2_RING3MWAIT

v7:
Change order of the patches, with this code looks cleaner.
Changed the name of MSR to MSR_MISC_FEATURE_ENABLES.
Used Word 3 25th bit to expose feature.

v6: 

v5:
When phir3mwait=disable is cmdline switch off r3 mwait feature
Fix typos

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

v3:
Included Daves and Thomas comments

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


Grzegorz Andrejczuk (4):
  x86/msr: Add MSR_MISC_FEATURE_ENABLES and PHIR3MWAIT bit
  x86/elf: Use HWCAP2 to expose ring 3 MWAIT
  x86/cpufeature: Add PHIR3MWAIT to CPU features
  x86/cpufeatures: Handle RING3MWAIT on Xeon Phi models

 Documentation/kernel-parameters.txt       |  5 ++++
 Documentation/x86/x86_64/boot-options.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               | 39 +++++++++++++++++++++++++++++++
 8 files changed, 74 insertions(+), 1 deletion(-)
 create mode 100644 arch/x86/include/uapi/asm/hwcap2.h

-- 
2.5.1

[PATCH v8: 1/4] x86/msr: Add MSR_MISC_FEATURE_ENABLES and PHIR3MWAIT bit

[Grzegorz Andrejczuk]

Intel Xeon Phi x200 (codenamed Knights Landing) allows to enable
MONITOR and MWAIT instructions outside of ring 0.

The feature is controlled by MSR MISC_FEATURE_ENABLES (0x140).
Setting bit 1 of this register enables it, so MONITOR and MWAIT
instructions do not cause invalid-opcode exceptions when invoked
outside of ring 0.
The feature MSR is not yet documented in the SDM. Here is
the relevant documentation:

Hex   Dec  Name                    Scope
140H  320  MISC_FEATURE_ENABLES    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..0fc220d 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_MISC_FEATURE_ENABLES	0x00000140
+#define MSR_MISC_FEATURE_ENABLES_PHIR3MWAIT_BIT	1
+#define MSR_MISC_FEATURE_ENABLES_PHIR3MWAIT	(1ULL << MSR_MISC_FEATURE_ENABLES_PHIR3MWAIT_BIT)
+
 #define MSR_IA32_TSC_DEADLINE		0x000006E0
 
 /* P4/Xeon+ specific */
-- 
2.5.1

[PATCH v8: 2/4] x86/elf: Use HWCAP2 to expose ring 3 MWAIT

[Grzegorz Andrejczuk]

Add HWCAP2 for x86 and reserve its bit 0 to expose
ring 3 mwait.

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..9e7c117
--- /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_RING3MWAIT		(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 v8: 3/4] x86/cpufeature: Add PHIR3MWAIT to CPU features

[Grzegorz Andrejczuk]

Add Intel Xeon Phi x200 (KnightsLanding) cpu feature - ring 3 monitor/mwait

Signed-off-by: Grzegorz Andrejczuk <grzegorz.andrejczuk@intel.com>
---
 arch/x86/include/asm/cpufeatures.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 92a8308..98414c5 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -100,7 +100,7 @@
 #define X86_FEATURE_XTOPOLOGY	( 3*32+22) /* cpu topology enum extensions */
 #define X86_FEATURE_TSC_RELIABLE ( 3*32+23) /* TSC is known to be reliable */
 #define X86_FEATURE_NONSTOP_TSC	( 3*32+24) /* TSC does not stop in C states */
-/* free, was #define X86_FEATURE_CLFLUSH_MONITOR ( 3*32+25) * "" clflush reqd with monitor */
+#define X86_FEATURE_PHIR3MWAIT	( 3*32+25) /* Xeon Phi x200 ring 3 MONITOR/MWAIT */
 #define X86_FEATURE_EXTD_APICID	( 3*32+26) /* has extended APICID (8 bits) */
 #define X86_FEATURE_AMD_DCM     ( 3*32+27) /* multi-node processor */
 #define X86_FEATURE_APERFMPERF	( 3*32+28) /* APERFMPERF */
-- 
2.5.1

[PATCH v8: 4/4] x86/cpufeatures: Handle RING3MWAIT on Xeon Phi models

[Grzegorz Andrejczuk]

Unfortunately presence of this feature cannot be detected
automatically (by reading some other MSR) therefore it is required
to do explicit check for the family and model of the cpu.

If processor is Intel Xeon Phi x200 RING3MWAIT feature is enabled
by setting cpu cap X86_FEATURE_PHIR3MWAIT and elf HWCAP2_RING3MWAIT.

Signed-off-by: Grzegorz Andrejczuk <grzegorz.andrejczuk@intel.com>
---
 Documentation/kernel-parameters.txt       |  5 ++++
 Documentation/x86/x86_64/boot-options.txt |  5 ++++
 arch/x86/kernel/cpu/intel.c               | 39 +++++++++++++++++++++++++++++++
 3 files changed, 49 insertions(+)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index a4f4d69..7754310 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=	[X86-64] Do not enable Intel Xeon Phi x200 ring 3 MONITOR/MWAIT
+			feature for all cpus.
+			Format: { disable }
+			See Documentation/x86/x86_64/boot-options.txt
+
 	pirq=		[SMP,APIC] Manual mp-table setup
 			See Documentation/x86/i386/IO-APIC.txt.
 
diff --git a/Documentation/x86/x86_64/boot-options.txt b/Documentation/x86/x86_64/boot-options.txt
index 0965a71..1a515e8 100644
--- a/Documentation/x86/x86_64/boot-options.txt
+++ b/Documentation/x86/x86_64/boot-options.txt
@@ -281,6 +281,11 @@ Debugging
 
   kstack=N	Print N words from the kernel stack in oops dumps.
 
+  phir3mwait=disable
+  Disables unconditional setting bit 1 of the MSR_MISC_FEATURE_ENABLES
+  for Intel Xeon Phi, this way administrator can switch off ring 3 mwait
+  feature.
+
 Miscellaneous
 
 	nogbpages
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index fcd484d..670dd98 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>
@@ -61,6 +63,41 @@ 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;
+	return 1;
+}
+__setup("phir3mwait=disable", phir3mwait_disable);
+
+static void probe_xeon_phi_r3mwait(struct cpuinfo_x86 *c)
+{
+	/*
+	 * Rign 3 MWAIT feature cannot be detected without
+	 * ugly model and family comparison.
+	 */
+	if (c->x86 != 6 || c->x86_model != INTEL_FAM6_XEON_PHI_KNL)
+		return;
+
+	if (phi_r3mwait_disabled) {
+		msr_clear_bit(MSR_MISC_FEATURE_ENABLES,
+			      MSR_MISC_FEATURE_ENABLES_PHIR3MWAIT_BIT);
+		return;
+	}
+
+	msr_set_bit(MSR_MISC_FEATURE_ENABLES,
+		    MSR_MISC_FEATURE_ENABLES_PHIR3MWAIT_BIT);
+	set_cpu_cap(c, X86_FEATURE_PHIR3MWAIT);
+	ELF_HWCAP2 |= HWCAP2_RING3MWAIT;
+}
+
+#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 +602,8 @@ 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

Re: [PATCH v8: 1/4] x86/msr: Add MSR_MISC_FEATURE_ENABLES and PHIR3MWAIT bit

[Borislav Petkov]

On Tue, Nov 01, 2016 at 11:14:47AM +0100, Grzegorz Andrejczuk wrote:
> Intel Xeon Phi x200 (codenamed Knights Landing) allows to enable
> MONITOR and MWAIT instructions outside of ring 0.
> 
> The feature is controlled by MSR MISC_FEATURE_ENABLES (0x140).
> Setting bit 1 of this register enables it, so MONITOR and MWAIT
> instructions do not cause invalid-opcode exceptions when invoked
> outside of ring 0.
> The feature MSR is not yet documented in the SDM. Here is
> the relevant documentation:
> 
> Hex   Dec  Name                    Scope
> 140H  320  MISC_FEATURE_ENABLES    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(+)

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

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
-- 

Re: [PATCH v8: 3/4] x86/cpufeature: Add PHIR3MWAIT to CPU features

[Borislav Petkov]

On Tue, Nov 01, 2016 at 11:14:49AM +0100, Grzegorz Andrejczuk wrote:
> Add Intel Xeon Phi x200 (KnightsLanding) cpu feature - ring 3 monitor/mwait

@tip guys: s/cpu/CPU/, s!monitor/mwait!MONITOR/MWAIT! and add a fullstop when committing.

> Signed-off-by: Grzegorz Andrejczuk <grzegorz.andrejczuk@intel.com>
> ---
>  arch/x86/include/asm/cpufeatures.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index 92a8308..98414c5 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -100,7 +100,7 @@
>  #define X86_FEATURE_XTOPOLOGY	( 3*32+22) /* cpu topology enum extensions */
>  #define X86_FEATURE_TSC_RELIABLE ( 3*32+23) /* TSC is known to be reliable */
>  #define X86_FEATURE_NONSTOP_TSC	( 3*32+24) /* TSC does not stop in C states */
> -/* free, was #define X86_FEATURE_CLFLUSH_MONITOR ( 3*32+25) * "" clflush reqd with monitor */
> +#define X86_FEATURE_PHIR3MWAIT	( 3*32+25) /* Xeon Phi x200 ring 3 MONITOR/MWAIT */
>  #define X86_FEATURE_EXTD_APICID	( 3*32+26) /* has extended APICID (8 bits) */
>  #define X86_FEATURE_AMD_DCM     ( 3*32+27) /* multi-node processor */
>  #define X86_FEATURE_APERFMPERF	( 3*32+28) /* APERFMPERF */
> --

Otherwise:

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

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
-- 

[PATCH v8 3/4] x86/cpufeature: Add PHIR3MWAIT to CPU features

[Grzegorz Andrejczuk]

Add Intel Xeon Phi x200 (KnightsLanding) CPU feature - ring 3 MONITOR/MWAIT.

Signed-off-by: Grzegorz Andrejczuk <grzegorz.andrejczuk@intel.com>
---
 arch/x86/include/asm/cpufeatures.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 92a8308..98414c5 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -100,7 +100,7 @@
 #define X86_FEATURE_XTOPOLOGY	( 3*32+22) /* cpu topology enum extensions */
 #define X86_FEATURE_TSC_RELIABLE ( 3*32+23) /* TSC is known to be reliable */
 #define X86_FEATURE_NONSTOP_TSC	( 3*32+24) /* TSC does not stop in C states */
-/* free, was #define X86_FEATURE_CLFLUSH_MONITOR ( 3*32+25) * "" clflush reqd with monitor */
+#define X86_FEATURE_PHIR3MWAIT	( 3*32+25) /* Xeon Phi x200 ring 3 MONITOR/MWAIT */
 #define X86_FEATURE_EXTD_APICID	( 3*32+26) /* has extended APICID (8 bits) */
 #define X86_FEATURE_AMD_DCM     ( 3*32+27) /* multi-node processor */
 #define X86_FEATURE_APERFMPERF	( 3*32+28) /* APERFMPERF */
-- 
2.5.1

Re: [PATCH v8: 1/4] x86/msr: Add MSR_MISC_FEATURE_ENABLES and PHIR3MWAIT bit

[Thomas Gleixner]

On Tue, 1 Nov 2016, Grzegorz Andrejczuk wrote:
>  
> +/* Intel Xeon Phi x200 ring 3 MONITOR/MWAIT */

Oh well. I asked you to make that whole PHI thing go away.

This is a feature which has nothing to do with PHI. It just happens to be
implemented on PHI. The FEATURES_ENABLES MSR is not at all PHI specific.

It's all about a feature which enables ring 3 mwait/monitor.

> +#define MSR_MISC_FEATURE_ENABLES	0x00000140
> +#define MSR_MISC_FEATURE_ENABLES_PHIR3MWAIT_BIT	1
> +#define MSR_MISC_FEATURE_ENABLES_PHIR3MWAIT	(1ULL << MSR_MISC_FEATURE_ENABLES_PHIR3MWAIT_BIT)
> +

You really try hard to get your crap behind me. Stop sending out half baken
shit every other day without addressing my review comments.

Your trust level approaches negative space.

Thanks,

	tglx

RE: [PATCH v8: 1/4] x86/msr: Add MSR_MISC_FEATURE_ENABLES and PHIR3MWAIT bit

[Andrejczuk, Grzegorz]

>>On Tue, 1 Nov 2016, Grzegorz Andrejczuk wrote:
>>  
>> +/* Intel Xeon Phi x200 ring 3 MONITOR/MWAIT */
>
>Oh well. I asked you to make that whole PHI thing go away. 
>
>This is a feature which has nothing to do with PHI. It just happens to be implemented on PHI. The FEATURES_ENABLES MSR is not at all PHI specific.
>
>It's all about a feature which enables ring 3 mwait/monitor.

This bit enables ring 3 MONITOR/MWAIT only on Xeon Phi. It is reserved for other architectures.
I think this will be confusing when I remove PHI.

>> +#define MSR_MISC_FEATURE_ENABLES	0x00000140
>> +#define MSR_MISC_FEATURE_ENABLES_PHIR3MWAIT_BIT	1
>> +#define MSR_MISC_FEATURE_ENABLES_PHIR3MWAIT	(1ULL << MSR_MISC_FEATURE_ENABLES_PHIR3MWAIT_BIT)
>> +
>
>You really try hard to get your crap behind me. Stop sending out half baken shit every other day without addressing my review comments.
>
>Your trust level approaches negative space. 
>
>Thanks,
>
>	tglx

Regards,
Grzegorz

RE: [PATCH v8: 1/4] x86/msr: Add MSR_MISC_FEATURE_ENABLES and PHIR3MWAIT bit

[Thomas Gleixner]

On Fri, 4 Nov 2016, Andrejczuk, Grzegorz wrote:
> >>On Tue, 1 Nov 2016, Grzegorz Andrejczuk wrote:
> >>  
> >> +/* Intel Xeon Phi x200 ring 3 MONITOR/MWAIT */
> >
> > Oh well. I asked you to make that whole PHI thing go away. 
> >
> > This is a feature which has nothing to do with PHI. It just happens to
> > be implemented on PHI. The FEATURES_ENABLES MSR is not at all PHI
> > specific.
> > It's all about a feature which enables ring 3 mwait/monitor.
> 
> This bit enables ring 3 MONITOR/MWAIT only on Xeon Phi. It is reserved
> for other architectures.  I think this will be confusing when I remove
> PHI.

It's reserved for other models simply because they do not implement it.

PHI is nothing special and the MSR is not PHI specific at all. It's used
for other features on other models, e.g. CPUID faulting (bit 0). That's
why PHI got bit 1.

Intel has so far been very consistent with MSRs which are implemented on
different models and it would be highly surprising if they would use a
different MSR/BIT when they bring that ring3 mwait feature to other models
than PHI. We make it PHI special when that happens, but for now there is
nothing PHI special, except that the only model which implements this is
PHI at the moment.

Thanks,

	tglx