linux-kernel - [tip: x86/cpu] x86/split_lock: Enumerate architectural split lock disable bit

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Message-ID: <167896465821.5837.11576952994116410374.tip-bot2@tip-bot2>
Date:   Thu, 16 Mar 2023 11:04:18 -0000
From:   "tip-bot2 for Fenghua Yu" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        "Borislav Petkov (AMD)" <bp@...en8.de>,
        Tony Luck <tony.luck@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/cpu] x86/split_lock: Enumerate architectural split lock disable bit

The following commit has been merged into the x86/cpu branch of tip:

Commit-ID:     d7ce15e1d4162ab5e56dead10d4ae69a6b5c8ee8
Gitweb:        https://git.kernel.org/tip/d7ce15e1d4162ab5e56dead10d4ae69a6b5c8ee8
Author:        Fenghua Yu <fenghua.yu@...el.com>
AuthorDate:    Wed, 01 Mar 2023 17:19:46 -08:00
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Thu, 16 Mar 2023 11:50:51 +01:00

x86/split_lock: Enumerate architectural split lock disable bit

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.

Originally-by: Dave Hansen <dave.hansen@...ux.intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Tony Luck <tony.luck@...el.com>
Link: https://lore.kernel.org/lkml/20220701131958.687066-1-fenghua.yu@intel.com/t/#mada243bee0915532a6adef6a9e32d244d1a9aef4
---
 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 291d416..1c648b0 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -1451,31 +1451,13 @@ 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),
 	{}
 };
 
@@ -1487,24 +1469,27 @@ 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();
 }