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[PATCH v10 5/7] x86/cpufeature: Detect CPUID faulting support

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  [PATCH v10 5/7] x86/cpufeature: Detect CPUID faulting support Kyle Huey <me@kylehuey.com> - 2016-11-08 19:50 +0100
    Re: [PATCH v10 5/7] x86/cpufeature: Detect CPUID faulting support Thomas Gleixner <tglx@linutronix.de> - 2016-11-08 20:20 +0100
      Re: [PATCH v10 5/7] x86/cpufeature: Detect CPUID faulting support Kyle Huey <me@kylehuey.com> - 2016-11-08 20:40 +0100
    Re: [PATCH v10 5/7] x86/cpufeature: Detect CPUID faulting support Borislav Petkov <bp@suse.de> - 2016-11-09 12:20 +0100

#1517462 — [PATCH v10 5/7] x86/cpufeature: Detect CPUID faulting support

Intel supports faulting on the CPUID instruction beginning with Ivy Bridge.
When enabled, the processor will fault on attempts to execute the CPUID
instruction with CPL>0. This will allow a ptracer to emulate the CPUID
instruction.

Bit 31 of MSR_PLATFORM_INFO advertises support for this feature. It is
documented in detail in Section 2.3.2 of
http://www.intel.com/content/dam/www/public/us/en/documents/application-notes/virtualization-technology-flexmigration-application-note.pdf

Detect support for this feature and expose it as X86_FEATURE_CPUID_FAULT.

Signed-off-by: Kyle Huey <khuey@kylehuey.com>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/include/asm/cpufeatures.h |  1 +
 arch/x86/include/asm/msr-index.h   |  2 ++
 arch/x86/kernel/cpu/scattered.c    | 22 +++++++++++++++++++++-
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index a396292..62962e8 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -184,16 +184,17 @@
  * Auxiliary flags: Linux defined - For features scattered in various
  * CPUID levels like 0x6, 0xA etc, word 7.
  *
  * Reuse free bits when adding new feature flags!
  */
 
 #define X86_FEATURE_CPB		( 7*32+ 2) /* AMD Core Performance Boost */
 #define X86_FEATURE_EPB		( 7*32+ 3) /* IA32_ENERGY_PERF_BIAS support */
+#define X86_FEATURE_CPUID_FAULT ( 7*32+ 4) /* Intel CPUID faulting */
 
 #define X86_FEATURE_HW_PSTATE	( 7*32+ 8) /* AMD HW-PState */
 #define X86_FEATURE_PROC_FEEDBACK ( 7*32+ 9) /* AMD ProcFeedbackInterface */
 
 #define X86_FEATURE_INTEL_PT	( 7*32+15) /* Intel Processor Trace */
 #define X86_FEATURE_AVX512_4VNNIW (7*32+16) /* AVX-512 Neural Network Instructions */
 #define X86_FEATURE_AVX512_4FMAPS (7*32+17) /* AVX-512 Multiply Accumulation Single precision */
 
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 78f3760..97fb50b 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -36,16 +36,18 @@
 #define EFER_LMSLE		(1<<_EFER_LMSLE)
 #define EFER_FFXSR		(1<<_EFER_FFXSR)
 
 /* Intel MSRs. Some also available on other CPUs */
 #define MSR_IA32_PERFCTR0		0x000000c1
 #define MSR_IA32_PERFCTR1		0x000000c2
 #define MSR_FSB_FREQ			0x000000cd
 #define MSR_PLATFORM_INFO		0x000000ce
+#define PLATINFO_CPUID_FAULT_BIT	31
+#define PLATINFO_CPUID_FAULT		(1ULL << PLATINFO_CPUID_FAULT_BIT)
 
 #define MSR_NHM_SNB_PKG_CST_CFG_CTL	0x000000e2
 #define NHM_C3_AUTO_DEMOTE		(1UL << 25)
 #define NHM_C1_AUTO_DEMOTE		(1UL << 26)
 #define ATM_LNC_C6_AUTO_DEMOTE		(1UL << 25)
 #define SNB_C1_AUTO_UNDEMOTE		(1UL << 27)
 #define SNB_C3_AUTO_UNDEMOTE		(1UL << 28)
 
diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
index 1db8dc4..97a340d 100644
--- a/arch/x86/kernel/cpu/scattered.c
+++ b/arch/x86/kernel/cpu/scattered.c
@@ -19,41 +19,61 @@ struct cpuid_bit {
 
 enum cpuid_regs {
 	CR_EAX = 0,
 	CR_ECX,
 	CR_EDX,
 	CR_EBX
 };
 
+struct msr_bit {
+	u16 feature;
+	u16 msr;
+	u8 bit;
+};
+
 void init_scattered_cpuid_features(struct cpuinfo_x86 *c)
 {
+	const struct cpuid_bit *cb;
+	const struct msr_bit *mb;
 	u32 max_level;
 	u32 regs[4];
-	const struct cpuid_bit *cb;
+	u64 msrval;
 
 	static const struct cpuid_bit cpuid_bits[] = {
 		{ X86_FEATURE_INTEL_PT,		CR_EBX,25, 0x00000007, 0 },
 		{ X86_FEATURE_AVX512_4VNNIW,	CR_EDX, 2, 0x00000007, 0 },
 		{ X86_FEATURE_AVX512_4FMAPS,	CR_EDX, 3, 0x00000007, 0 },
 		{ X86_FEATURE_APERFMPERF,	CR_ECX, 0, 0x00000006, 0 },
 		{ X86_FEATURE_EPB,		CR_ECX, 3, 0x00000006, 0 },
 		{ X86_FEATURE_HW_PSTATE,	CR_EDX, 7, 0x80000007, 0 },
 		{ X86_FEATURE_CPB,		CR_EDX, 9, 0x80000007, 0 },
 		{ X86_FEATURE_PROC_FEEDBACK,	CR_EDX,11, 0x80000007, 0 },
 		{ 0, 0, 0, 0, 0 }
 	};
 
+	static const struct msr_bit msr_bits[] = {
+		{ X86_FEATURE_CPUID_FAULT,	MSR_PLATFORM_INFO, 31 },
+		{ 0, 0, 0 }
+	};
+
 	for (cb = cpuid_bits; cb->feature; cb++) {
 
 		/* Verify that the level is valid */
 		max_level = cpuid_eax(cb->level & 0xffff0000);
 		if (max_level < cb->level ||
 		    max_level > (cb->level | 0xffff))
 			continue;
 
 		cpuid_count(cb->level, cb->sub_leaf, &regs[CR_EAX],
 			    &regs[CR_EBX], &regs[CR_ECX], &regs[CR_EDX]);
 
 		if (regs[cb->reg] & (1 << cb->bit))
 			set_cpu_cap(c, cb->feature);
 	}
+
+	for (mb = msr_bits; mb->feature; mb++) {
+		if (rdmsrl_safe(mb->msr, &msrval))
+			continue;
+		if (msrval & (1ULL << mb->bit))
+			set_cpu_cap(c, mb->feature);
+	}
 }
-- 
2.10.2

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#1517507

On Tue, 8 Nov 2016, Kyle Huey wrote:

> Intel supports faulting on the CPUID instruction beginning with Ivy Bridge.
> When enabled, the processor will fault on attempts to execute the CPUID
> instruction with CPL>0. This will allow a ptracer to emulate the CPUID
> instruction.
> 
> Bit 31 of MSR_PLATFORM_INFO advertises support for this feature. It is
> documented in detail in Section 2.3.2 of
> http://www.intel.com/content/dam/www/public/us/en/documents/application-notes/virtualization-technology-flexmigration-application-note.pdf

Can you please stick that document into the kernel bugzilla, as it's going
to be on a different place before this gets merged into Linus tree?

See: http://lkml.kernel.org/r/1478631281-5061-1-git-send-email-kan.liang@intel.com

> +	static const struct msr_bit msr_bits[] = {
> +		{ X86_FEATURE_CPUID_FAULT,	MSR_PLATFORM_INFO, 31 },

Can you please make that PLATINFO_CPUID_FAULT_BIT instead of 31?

Thanks,

	tglx

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#1517517

On Tue, Nov 8, 2016 at 11:06 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> On Tue, 8 Nov 2016, Kyle Huey wrote:
>
>> Intel supports faulting on the CPUID instruction beginning with Ivy Bridge.
>> When enabled, the processor will fault on attempts to execute the CPUID
>> instruction with CPL>0. This will allow a ptracer to emulate the CPUID
>> instruction.
>>
>> Bit 31 of MSR_PLATFORM_INFO advertises support for this feature. It is
>> documented in detail in Section 2.3.2 of
>> http://www.intel.com/content/dam/www/public/us/en/documents/application-notes/virtualization-technology-flexmigration-application-note.pdf

Done. https://bugzilla.kernel.org/attachment.cgi?id=243991

> Can you please stick that document into the kernel bugzilla, as it's going
> to be on a different place before this gets merged into Linus tree?
>
> See: http://lkml.kernel.org/r/1478631281-5061-1-git-send-email-kan.liang@intel.com
>
>> +     static const struct msr_bit msr_bits[] = {
>> +             { X86_FEATURE_CPUID_FAULT,      MSR_PLATFORM_INFO, 31 },
>
> Can you please make that PLATINFO_CPUID_FAULT_BIT instead of 31?

Sure.

- Kyle

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#1517979

On Tue, Nov 08, 2016 at 10:39:54AM -0800, Kyle Huey wrote:
> Intel supports faulting on the CPUID instruction beginning with Ivy Bridge.
> When enabled, the processor will fault on attempts to execute the CPUID
> instruction with CPL>0. This will allow a ptracer to emulate the CPUID
> instruction.
> 
> Bit 31 of MSR_PLATFORM_INFO advertises support for this feature. It is
> documented in detail in Section 2.3.2 of
> http://www.intel.com/content/dam/www/public/us/en/documents/application-notes/virtualization-technology-flexmigration-application-note.pdf
> 
> Detect support for this feature and expose it as X86_FEATURE_CPUID_FAULT.
> 
> Signed-off-by: Kyle Huey <khuey@kylehuey.com>
> Reviewed-by: Andy Lutomirski <luto@kernel.org>
> ---
>  arch/x86/include/asm/cpufeatures.h |  1 +
>  arch/x86/include/asm/msr-index.h   |  2 ++
>  arch/x86/kernel/cpu/scattered.c    | 22 +++++++++++++++++++++-
>  3 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index a396292..62962e8 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -184,16 +184,17 @@
>   * Auxiliary flags: Linux defined - For features scattered in various
>   * CPUID levels like 0x6, 0xA etc, word 7.
>   *
>   * Reuse free bits when adding new feature flags!
>   */
>  
>  #define X86_FEATURE_CPB		( 7*32+ 2) /* AMD Core Performance Boost */
>  #define X86_FEATURE_EPB		( 7*32+ 3) /* IA32_ENERGY_PERF_BIAS support */
> +#define X86_FEATURE_CPUID_FAULT ( 7*32+ 4) /* Intel CPUID faulting */

Bit 0 in that leaf is free. Also, bit 4 is already claimed by RDT/CAT/...
whatever that thing is going to be called so please do:

#define X86_FEATURE_CPUID_FAULT ( 7*32+ 0) /* Intel CPUID faulting */

>  
>  #define X86_FEATURE_HW_PSTATE	( 7*32+ 8) /* AMD HW-PState */
>  #define X86_FEATURE_PROC_FEEDBACK ( 7*32+ 9) /* AMD ProcFeedbackInterface */
>  
>  #define X86_FEATURE_INTEL_PT	( 7*32+15) /* Intel Processor Trace */
>  #define X86_FEATURE_AVX512_4VNNIW (7*32+16) /* AVX-512 Neural Network Instructions */
>  #define X86_FEATURE_AVX512_4FMAPS (7*32+17) /* AVX-512 Multiply Accumulation Single precision */

...

>  	for (cb = cpuid_bits; cb->feature; cb++) {
>  
>  		/* Verify that the level is valid */
>  		max_level = cpuid_eax(cb->level & 0xffff0000);
>  		if (max_level < cb->level ||
>  		    max_level > (cb->level | 0xffff))
>  			continue;
>  
>  		cpuid_count(cb->level, cb->sub_leaf, &regs[CR_EAX],
>  			    &regs[CR_EBX], &regs[CR_ECX], &regs[CR_EDX]);
>  
>  		if (regs[cb->reg] & (1 << cb->bit))
>  			set_cpu_cap(c, cb->feature);
>  	}
> +
> +	for (mb = msr_bits; mb->feature; mb++) {
> +		if (rdmsrl_safe(mb->msr, &msrval))
> +			continue;

<--- newline here.

> +		if (msrval & (1ULL << mb->bit))

		if (msrval & BIT_ULL(mb->bit))


> +			set_cpu_cap(c, mb->feature);
> +	}
>  }
> -- 

-- 
Regards/Gruss,
    Boris.

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

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