linux-kernel - [PATCH] x86/cpu: Drop vestigial PBE logic in AMD/Hygon/Centaur/Cyrix

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: <20251126125147.880275-1-andrew.cooper3@citrix.com>
Date: Wed, 26 Nov 2025 12:51:47 +0000
From: Andrew Cooper <andrew.cooper3@...rix.com>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Andrew Cooper <andrew.cooper3@...rix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Pu Wen <puwen@...on.cn>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	x86@...nel.org
Subject: [PATCH] x86/cpu: Drop vestigial PBE logic in AMD/Hygon/Centaur/Cyrix

Besides formatting changes, this logic dates back to Linux 2.4.0-test11 in
November 2000.

Prior to "Massive cleanup of CPU detection and bug handling",
c->x86_capability was a single u32 containing cpuid(1).edx,
cpuid(0x80000001).edx, or a synthesis thereof.  X86_FEATURE_AMD3D was
defined as the top bit this single u32.

After "Massive cleanup of CPU detection and bug handling",
c->x86_capability became an array with AMD's extended feature leaf split
away from Intel's basic feature leaf.

AMD doc #20734-G states that 3DNow is only enumerated in the extended
feature leaf, and that other vendors where using this bit too.  i.e. AMD
never produced a CPU which set bit 31 in the basic leaf, meaning that
there's nothing to clear out in the first place.

This logic looks like it was relevant in the pre-"Massive cleanup" world
but ought to have been dropped when c->x86_capability was properly split.

Signed-off-by: Andrew Cooper <andrew.cooper3@...rix.com>
---
CC: Thomas Gleixner <tglx@...utronix.de>
CC: Ingo Molnar <mingo@...hat.com>
CC: Borislav Petkov <bp@...en8.de>
CC: Dave Hansen <dave.hansen@...ux.intel.com>
CC: "H. Peter Anvin" <hpa@...or.com>
CC: Pu Wen <puwen@...on.cn> (maintainer:HYGON PROCESSOR SUPPORT)
CC: "Peter Zijlstra (Intel)" <peterz@...radead.org>
CC: x86@...nel.org
CC: linux-kernel@...r.kernel.org

I'm not sure how best to represent:

https://github.com/schwabe/davej-history/commit/67ad24e6d39c3bc4618e7eb0563ccde3d76d0a51#diff-ab4c065cef7ebcd6d255c47ed4c3c0a77da8ad3df004dab9a183cc88814730ff

in the commit message.

git://git.kernel.org/pub/scm/linux/kernel/git/davej/history.git doesn't
appear to exist any more.

In principle this wants a fixes tag to 25 years ago, but I don't think it's
important enough to warrant backporting.
---
 arch/x86/kernel/cpu/amd.c     | 6 ------
 arch/x86/kernel/cpu/centaur.c | 6 ------
 arch/x86/kernel/cpu/cyrix.c   | 6 ------
 arch/x86/kernel/cpu/hygon.c   | 6 ------
 4 files changed, 24 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 505ff37b850c..73d634bc8e98 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -1051,12 +1051,6 @@ static void init_amd(struct cpuinfo_x86 *c)
 
 	early_init_amd(c);
 
-	/*
-	 * Bit 31 in normal CPUID used for nonstandard 3DNow ID;
-	 * 3DNow is IDd by bit 31 in extended CPUID (1*32+31) anyway
-	 */
-	clear_cpu_cap(c, 0*32+31);
-
 	if (c->x86 >= 0x10)
 		set_cpu_cap(c, X86_FEATURE_REP_GOOD);
 
diff --git a/arch/x86/kernel/cpu/centaur.c b/arch/x86/kernel/cpu/centaur.c
index a3b55db35c96..c8398940b975 100644
--- a/arch/x86/kernel/cpu/centaur.c
+++ b/arch/x86/kernel/cpu/centaur.c
@@ -119,12 +119,6 @@ static void init_centaur(struct cpuinfo_x86 *c)
 	u32  fcr_clr = 0;
 	u32  lo, hi, newlo;
 	u32  aa, bb, cc, dd;
-
-	/*
-	 * Bit 31 in normal CPUID used for nonstandard 3DNow ID;
-	 * 3DNow is IDd by bit 31 in extended CPUID (1*32+31) anyway
-	 */
-	clear_cpu_cap(c, 0*32+31);
 #endif
 	early_init_centaur(c);
 	init_intel_cacheinfo(c);
diff --git a/arch/x86/kernel/cpu/cyrix.c b/arch/x86/kernel/cpu/cyrix.c
index dfec2c61e354..8f22085c4dd2 100644
--- a/arch/x86/kernel/cpu/cyrix.c
+++ b/arch/x86/kernel/cpu/cyrix.c
@@ -195,12 +195,6 @@ static void init_cyrix(struct cpuinfo_x86 *c)
 	char *buf = c->x86_model_id;
 	const char *p = NULL;
 
-	/*
-	 * Bit 31 in normal CPUID used for nonstandard 3DNow ID;
-	 * 3DNow is IDd by bit 31 in extended CPUID (1*32+31) anyway
-	 */
-	clear_cpu_cap(c, 0*32+31);
-
 	/* Cyrix used bit 24 in extended (AMD) CPUID for Cyrix MMX extensions */
 	if (test_cpu_cap(c, 1*32+24)) {
 		clear_cpu_cap(c, 1*32+24);
diff --git a/arch/x86/kernel/cpu/hygon.c b/arch/x86/kernel/cpu/hygon.c
index 1fda6c3a2b65..7f95a74e4c65 100644
--- a/arch/x86/kernel/cpu/hygon.c
+++ b/arch/x86/kernel/cpu/hygon.c
@@ -174,12 +174,6 @@ static void init_hygon(struct cpuinfo_x86 *c)
 
 	early_init_hygon(c);
 
-	/*
-	 * Bit 31 in normal CPUID used for nonstandard 3DNow ID;
-	 * 3DNow is IDd by bit 31 in extended CPUID (1*32+31) anyway
-	 */
-	clear_cpu_cap(c, 0*32+31);
-
 	set_cpu_cap(c, X86_FEATURE_REP_GOOD);
 
 	/*

base-commit: ac3fd01e4c1efce8f2c054cdeb2ddd2fc0fb150d
-- 
2.39.5