linux-kernel - [PATCH] x86/cpufeatures: Free up unused feature bits

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Message-Id: <20241107233000.2742619-1-sohil.mehta@intel.com>
Date: Thu,  7 Nov 2024 23:30:00 +0000
From: Sohil Mehta <sohil.mehta@...el.com>
To: x86@...nel.org,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Sohil Mehta <sohil.mehta@...el.com>,
	Sean Christopherson <seanjc@...gle.com>,
	Tony Luck <tony.luck@...el.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] x86/cpufeatures: Free up unused feature bits

Linux defined feature bits X86_FEATURE_P3 and X86_FEATURE_P4 are not
used anywhere, neither are they visible to userspace.
commit f31d731e4467 ("x86: use X86_FEATURE_NOPL in alternatives") got
rid of the last usage. Remove the related mappings and code.

Signed-off-by: Sohil Mehta <sohil.mehta@...el.com>
---
 arch/x86/include/asm/cpufeatures.h | 4 ++--
 arch/x86/kernel/cpu/intel.c        | 5 -----
 2 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 913fd3a7bac6..f5c4ea3fd364 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -83,8 +83,8 @@
 #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 */
-#define X86_FEATURE_P3			( 3*32+ 6) /* P3 */
-#define X86_FEATURE_P4			( 3*32+ 7) /* P4 */
+/* Free                                 ( 3*32+ 6) */
+/* 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 */
 #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 e7656cbef68d..1c892ebaa68c 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -628,11 +628,6 @@ static void init_intel(struct cpuinfo_x86 *c)
 		if (p)
 			strcpy(c->x86_model_id, p);
 	}
-
-	if (c->x86 == 15)
-		set_cpu_cap(c, X86_FEATURE_P4);
-	if (c->x86 == 6)
-		set_cpu_cap(c, X86_FEATURE_P3);
 #endif
 
 	/* Work around errata */
-- 
2.34.1