[PATCH] x86/split_lock: Enumerate architectural split lock disable bit

[PATCH] x86/split_lock: Enumerate architectural split lock disable bit

[Fenghua Yu]

The December 2022 edition of the Intel Instruction Set Extensions manual
defined that the split lock disable bit in the IA32_CORE_CAPABILITIES MSR
is (and retrospectively always has been) architectural.

Remove all the model specific checks except for Ice Lake variants which are
still needed because these CPU models do not enumerate presence of the
IA32_CORE_CAPABILITIES MSR.

Link: https://lore.kernel.org/lkml/20220701131958.687066-1-fenghua.yu@intel.com/t/#mada243bee0915532a6adef6a9e32d244d1a9aef4
Originally-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
---
 arch/x86/kernel/cpu/intel.c | 59 ++++++++++++++-----------------------
 1 file changed, 22 insertions(+), 37 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 2d7ea5480ec3..d27f8973b58f 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -1266,31 +1266,13 @@ void handle_bus_lock(struct pt_regs *regs)
 }
 
 /*
- * Bits in the IA32_CORE_CAPABILITIES are not architectural, so they should
- * only be trusted if it is confirmed that a CPU model implements a
- * specific feature at a particular bit position.
- *
- * The possible driver data field values:
- *
- * - 0: CPU models that are known to have the per-core split-lock detection
- *	feature even though they do not enumerate IA32_CORE_CAPABILITIES.
- *
- * - 1: CPU models which may enumerate IA32_CORE_CAPABILITIES and if so use
- *      bit 5 to enumerate the per-core split-lock detection feature.
+ * CPU models that are known to have the per-core split-lock detection
+ * feature even though they do not enumerate IA32_CORE_CAPABILITIES.
  */
 static const struct x86_cpu_id split_lock_cpu_ids[] __initconst = {
-	X86_MATCH_INTEL_FAM6_MODEL(ICELAKE_X,		0),
-	X86_MATCH_INTEL_FAM6_MODEL(ICELAKE_L,		0),
-	X86_MATCH_INTEL_FAM6_MODEL(ICELAKE_D,		0),
-	X86_MATCH_INTEL_FAM6_MODEL(ATOM_TREMONT,	1),
-	X86_MATCH_INTEL_FAM6_MODEL(ATOM_TREMONT_D,	1),
-	X86_MATCH_INTEL_FAM6_MODEL(ATOM_TREMONT_L,	1),
-	X86_MATCH_INTEL_FAM6_MODEL(TIGERLAKE_L,		1),
-	X86_MATCH_INTEL_FAM6_MODEL(TIGERLAKE,		1),
-	X86_MATCH_INTEL_FAM6_MODEL(SAPPHIRERAPIDS_X,	1),
-	X86_MATCH_INTEL_FAM6_MODEL(ALDERLAKE,		1),
-	X86_MATCH_INTEL_FAM6_MODEL(ALDERLAKE_L,		1),
-	X86_MATCH_INTEL_FAM6_MODEL(RAPTORLAKE,		1),
+	X86_MATCH_INTEL_FAM6_MODEL(ICELAKE_X,	0),
+	X86_MATCH_INTEL_FAM6_MODEL(ICELAKE_L,	0),
+	X86_MATCH_INTEL_FAM6_MODEL(ICELAKE_D,	0),
 	{}
 };
 
@@ -1302,24 +1284,27 @@ static void __init split_lock_setup(struct cpuinfo_x86 *c)
 	if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
 		return;
 
+	/* Check for CPUs that have support but do not enumerate it: */
 	m = x86_match_cpu(split_lock_cpu_ids);
-	if (!m)
-		return;
+	if (m)
+		goto supported;
 
-	switch (m->driver_data) {
-	case 0:
-		break;
-	case 1:
-		if (!cpu_has(c, X86_FEATURE_CORE_CAPABILITIES))
-			return;
-		rdmsrl(MSR_IA32_CORE_CAPS, ia32_core_caps);
-		if (!(ia32_core_caps & MSR_IA32_CORE_CAPS_SPLIT_LOCK_DETECT))
-			return;
-		break;
-	default:
+	if (!cpu_has(c, X86_FEATURE_CORE_CAPABILITIES))
 		return;
-	}
 
+	/*
+	 * Not all bits in MSR_IA32_CORE_CAPS are architectural, but
+	 * MSR_IA32_CORE_CAPS_SPLIT_LOCK_DETECT is.  All CPUs that set
+	 * it have split lock detection.
+	 */
+	rdmsrl(MSR_IA32_CORE_CAPS, ia32_core_caps);
+	if (ia32_core_caps & MSR_IA32_CORE_CAPS_SPLIT_LOCK_DETECT)
+		goto supported;
+
+	/* CPU is not in the model list and does not have the MSR bit: */
+	return;
+
+supported:
 	cpu_model_supports_sld = true;
 	__split_lock_setup();
 }
-- 
2.32.0

Re: [PATCH] x86/split_lock: Enumerate architectural split lock disable bit

[Fenghua Yu]

Hi, Dear X86 Maintainers,

On 3/1/23 17:19, Fenghua Yu wrote:
> The December 2022 edition of the Intel Instruction Set Extensions manual
> defined that the split lock disable bit in the IA32_CORE_CAPABILITIES MSR
> is (and retrospectively always has been) architectural.
> 
> Remove all the model specific checks except for Ice Lake variants which are
> still needed because these CPU models do not enumerate presence of the
> IA32_CORE_CAPABILITIES MSR.
> 
> Link: https://lore.kernel.org/lkml/20220701131958.687066-1-fenghua.yu@intel.com/t/#mada243bee0915532a6adef6a9e32d244d1a9aef4
> Originally-by: Dave Hansen <dave.hansen@linux.intel.com>
> Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> ---
>   arch/x86/kernel/cpu/intel.c | 59 ++++++++++++++-----------------------
>   1 file changed, 22 insertions(+), 37 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> index 2d7ea5480ec3..d27f8973b58f 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -1266,31 +1266,13 @@ void handle_bus_lock(struct pt_regs *regs)
>   }
>   
>   /*
> - * Bits in the IA32_CORE_CAPABILITIES are not architectural, so they should
> - * only be trusted if it is confirmed that a CPU model implements a
> - * specific feature at a particular bit position.
> - *
> - * The possible driver data field values:
> - *
> - * - 0: CPU models that are known to have the per-core split-lock detection
> - *	feature even though they do not enumerate IA32_CORE_CAPABILITIES.
> - *
> - * - 1: CPU models which may enumerate IA32_CORE_CAPABILITIES and if so use
> - *      bit 5 to enumerate the per-core split-lock detection feature.
> + * CPU models that are known to have the per-core split-lock detection
> + * feature even though they do not enumerate IA32_CORE_CAPABILITIES.
>    */
>   static const struct x86_cpu_id split_lock_cpu_ids[] __initconst = {
> -	X86_MATCH_INTEL_FAM6_MODEL(ICELAKE_X,		0),
> -	X86_MATCH_INTEL_FAM6_MODEL(ICELAKE_L,		0),
> -	X86_MATCH_INTEL_FAM6_MODEL(ICELAKE_D,		0),
> -	X86_MATCH_INTEL_FAM6_MODEL(ATOM_TREMONT,	1),
> -	X86_MATCH_INTEL_FAM6_MODEL(ATOM_TREMONT_D,	1),
> -	X86_MATCH_INTEL_FAM6_MODEL(ATOM_TREMONT_L,	1),
> -	X86_MATCH_INTEL_FAM6_MODEL(TIGERLAKE_L,		1),
> -	X86_MATCH_INTEL_FAM6_MODEL(TIGERLAKE,		1),
> -	X86_MATCH_INTEL_FAM6_MODEL(SAPPHIRERAPIDS_X,	1),
> -	X86_MATCH_INTEL_FAM6_MODEL(ALDERLAKE,		1),
> -	X86_MATCH_INTEL_FAM6_MODEL(ALDERLAKE_L,		1),
> -	X86_MATCH_INTEL_FAM6_MODEL(RAPTORLAKE,		1),
> +	X86_MATCH_INTEL_FAM6_MODEL(ICELAKE_X,	0),
> +	X86_MATCH_INTEL_FAM6_MODEL(ICELAKE_L,	0),
> +	X86_MATCH_INTEL_FAM6_MODEL(ICELAKE_D,	0),
>   	{}
>   };
>   
> @@ -1302,24 +1284,27 @@ static void __init split_lock_setup(struct cpuinfo_x86 *c)
>   	if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
>   		return;
>   
> +	/* Check for CPUs that have support but do not enumerate it: */
>   	m = x86_match_cpu(split_lock_cpu_ids);
> -	if (!m)
> -		return;
> +	if (m)
> +		goto supported;
>   
> -	switch (m->driver_data) {
> -	case 0:
> -		break;
> -	case 1:
> -		if (!cpu_has(c, X86_FEATURE_CORE_CAPABILITIES))
> -			return;
> -		rdmsrl(MSR_IA32_CORE_CAPS, ia32_core_caps);
> -		if (!(ia32_core_caps & MSR_IA32_CORE_CAPS_SPLIT_LOCK_DETECT))
> -			return;
> -		break;
> -	default:
> +	if (!cpu_has(c, X86_FEATURE_CORE_CAPABILITIES))
>   		return;
> -	}
>   
> +	/*
> +	 * Not all bits in MSR_IA32_CORE_CAPS are architectural, but
> +	 * MSR_IA32_CORE_CAPS_SPLIT_LOCK_DETECT is.  All CPUs that set
> +	 * it have split lock detection.
> +	 */
> +	rdmsrl(MSR_IA32_CORE_CAPS, ia32_core_caps);
> +	if (ia32_core_caps & MSR_IA32_CORE_CAPS_SPLIT_LOCK_DETECT)
> +		goto supported;
> +
> +	/* CPU is not in the model list and does not have the MSR bit: */
> +	return;
> +
> +supported:
>   	cpu_model_supports_sld = true;
>   	__split_lock_setup();
>   }

Any comment on this patch?

If this patch is in upstream, we won't continuously send model specific 
enumeration patches for future processors.

Thanks.

-Fenghua