linux-kernel - [RFC PATCH 4/9] x86/mm: Introduce X86_FEATURE

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Message-ID: <20250506003811.92405-5-riel@surriel.com>
Date: Mon,  5 May 2025 20:37:42 -0400
From: Rik van Riel <riel@...riel.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
	x86@...nel.org,
	kernel-team@...a.com,
	dave.hansen@...ux.intel.com,
	luto@...nel.org,
	peterz@...radead.org,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	hpa@...or.com,
	Rik van Riel <riel@...com>,
	Yu-cheng Yu <yu-cheng.yu@...el.com>,
	Rik van Riel <riel@...riel.com>
Subject: [RFC PATCH 4/9] x86/mm: Introduce X86_FEATURE_RAR

From: Rik van Riel <riel@...com>

Introduce X86_FEATURE_RAR and enumeration of the feature.

[riel: move 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/common.c       | 13 +++++++++++++
 3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig.cpufeatures b/arch/x86/Kconfig.cpufeatures
index e12d5b7e39a2..60042f8c2837 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 7642310276a8..06732c872998 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -75,7 +75,7 @@
 #define X86_FEATURE_CENTAUR_MCR		( 3*32+ 3) /* "centaur_mcr" Centaur MCRs (= MTRRs) */
 #define X86_FEATURE_K8			( 3*32+ 4) /* Opteron, Athlon64 */
 #define X86_FEATURE_ZEN5		( 3*32+ 5) /* CPU based on Zen5 microarchitecture */
-/* Free                                 ( 3*32+ 6) */
+#define X86_FEATURE_RAR			( 3*32+ 6) /* Intel Remote Action Request */
 /* Free                                 ( 3*32+ 7) */
 #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 */
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index b73e09315413..5666620e7153 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1502,6 +1502,18 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
 	setup_force_cpu_bug(X86_BUG_L1TF);
 }
 
+static void __init detect_rar(struct cpuinfo_x86 *c)
+{
+	u64 msr;
+
+	if (cpu_has(c, X86_FEATURE_CORE_CAPABILITIES)) {
+		rdmsrl(MSR_IA32_CORE_CAPABILITIES, msr);
+
+		if (msr & CORE_CAP_RAR)
+			setup_force_cpu_cap(X86_FEATURE_RAR);
+	}
+}
+
 /*
  * The NOPL instruction is supposed to exist on all CPUs of family >= 6;
  * unfortunately, that's not true in practice because of early VIA
@@ -1728,6 +1740,7 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
 		setup_clear_cpu_cap(X86_FEATURE_LA57);
 
 	detect_nopl();
+	detect_rar(c);
 }
 
 void __init init_cpu_devs(void)
-- 
2.49.0