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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <173348021509.412.6713554902949596363.tip-bot2@tip-bot2>
Date: Fri, 06 Dec 2024 10:16:55 -0000
From: "tip-bot2 for Sohil Mehta" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Sohil Mehta <sohil.mehta@...el.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>, Ingo Molnar <mingo@...nel.org>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/cpu] x86/cpufeatures: Free up unused feature bits

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

Commit-ID:     7a470e826d7521bec6af789deab31cfa4fd05af3
Gitweb:        https://git.kernel.org/tip/7a470e826d7521bec6af789deab31cfa4fd05af3
Author:        Sohil Mehta <sohil.mehta@...el.com>
AuthorDate:    Thu, 07 Nov 2024 23:30:00 
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Fri, 06 Dec 2024 10:57:44 +01:00

x86/cpufeatures: Free up unused feature bits

Linux defined feature bits X86_FEATURE_P3 and X86_FEATURE_P4 are not
used anywhere. Commit f31d731e4467 ("x86: use X86_FEATURE_NOPL in
alternatives") got rid of the last usage in 2008. Remove the related
mappings and code.

Just like all X86_FEATURE bits, the raw bit numbers can be exposed to
userspace via MODULE_DEVICE_TABLE(). There is a very small theoretical
chance of userspace getting confused if these bits got reassigned and
changed logical meaning.  But these bits were never used for a device
table, so it's highly unlikely this will ever happen in practice.

[ dhansen: clarify userspace visibility of these bits ]

Signed-off-by: Sohil Mehta <sohil.mehta@...el.com>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Link: https://lore.kernel.org/all/20241107233000.2742619-1-sohil.mehta%40intel.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 17b6590..f725ccc 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 d1de300..5a9fbe9 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -597,11 +597,6 @@ 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 */