linux-kernel - [RFC v5 3/8] x86/mm: Introduce X86_FEATURE

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Message-ID: <20251121185530.21876-4-riel@surriel.com>
Date: Fri, 21 Nov 2025 13:54:24 -0500
From: Rik van Riel <riel@...riel.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
	x86@...nel.org,
	dave.hansen@...ux.intel.com,
	peterz@...radead.org,
	kernel-team@...a.com,
	bp@...en8.de,
	Yu-cheng Yu <yu-cheng.yu@...el.com>,
	Rik van Riel <riel@...riel.com>
Subject: [RFC v5 3/8] x86/mm: Introduce X86_FEATURE_RAR

From: Yu-cheng Yu <yu-cheng.yu@...el.com>

Introduce X86_FEATURE_RAR and enumeration of the feature.

[riel: moved initialization to intel.c and disabling to Kconfig.cpufeatures]

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
Signed-off-by: Rik van Riel <riel@...riel.com>
---
 arch/x86/Kconfig.cpufeatures       | 4 ++++
 arch/x86/include/asm/cpufeatures.h | 2 +-
 arch/x86/kernel/cpu/intel.c        | 9 +++++++++
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig.cpufeatures b/arch/x86/Kconfig.cpufeatures
index 733d5aff2456..6389f0a617c8 100644
--- a/arch/x86/Kconfig.cpufeatures
+++ b/arch/x86/Kconfig.cpufeatures
@@ -199,3 +199,7 @@ config X86_DISABLED_FEATURE_SEV_SNP
 config X86_DISABLED_FEATURE_INVLPGB
 	def_bool y
 	depends on !BROADCAST_TLB_FLUSH
+
+config X86_DISABLED_FEATURE_RAR
+	def_bool y
+	depends on !BROADCAST_TLB_FLUSH
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index b6472e252491..5cb57a820198 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -76,7 +76,7 @@
 #define X86_FEATURE_K8			( 3*32+ 4) /* Opteron, Athlon64 */
 #define X86_FEATURE_ZEN5		( 3*32+ 5) /* CPU based on Zen5 microarchitecture */
 #define X86_FEATURE_ZEN6		( 3*32+ 6) /* CPU based on Zen6 microarchitecture */
-/* Free                                 ( 3*32+ 7) */
+#define X86_FEATURE_RAR			( 3*32+ 7) /* Intel Remote Action Request */
 #define X86_FEATURE_CONSTANT_TSC	( 3*32+ 8) /* "constant_tsc" TSC ticks at a constant rate */
 #define X86_FEATURE_UP			( 3*32+ 9) /* "up" SMP kernel running on UP */
 #define X86_FEATURE_ART			( 3*32+10) /* "art" Always running timer (ART) */
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 98ae4c37c93e..b53bf3452d6a 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -719,6 +719,15 @@ static void intel_detect_tlb(struct cpuinfo_x86 *c)
 	cpuid_leaf_0x2(&regs);
 	for_each_cpuid_0x2_desc(regs, ptr, desc)
 		intel_tlb_lookup(desc);
+
+	if (cpu_has(c, X86_FEATURE_CORE_CAPABILITIES)) {
+		u64 msr;
+
+		rdmsrl(MSR_IA32_CORE_CAPS, msr);
+
+		if (msr & MSR_IA32_CORE_CAPS_RAR)
+			setup_force_cpu_cap(X86_FEATURE_RAR);
+	}
 }
 
 static const struct cpu_dev intel_cpu_dev = {
-- 
2.51.1