From nobody Sun Feb 8 13:44:59 2026 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9102525E825; Wed, 9 Apr 2025 12:04:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744200302; cv=none; b=rrOP6Hx8yqFeHS80bhVgkAM3uVpIp3UMwwZ6LHwE3tblvubFFhc10y2uLK12bBpRSXjw6gw2w4vVBcoA/lcTMkrTYBWnsxrs0zQhpXe+FwF0AMU7NMAHv7hULg4ji1X1PtYpKmflgkQ8PCf+ikRSxQQRLFBvWlCi8McXz/s8eH8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744200302; c=relaxed/simple; bh=GlZwCY4BAgacwhTavkIs9jTWFfuHo5KprQF5+BHZN7w=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=F+5aKz90LWtzbbGINET+QH8b/2KPjOFDOmr/5/Jk/it2a2GgZ2vJUlfZug0rjm/P4+fh5Y6W+j9T3CtEkG1bIL/MsFt7/f+9qk4JBCjVd7LsYGoobPGh/JaLjZvnbXu91a/9XILtfsm9x3PNLZwMNvCgd9xMpCCVvvS9q+i/xPs= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=iYGxWCao; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=Yxt+dh9w; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="iYGxWCao"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="Yxt+dh9w" Date: Wed, 09 Apr 2025 12:04:56 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1744200297; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=LBtR6S8RUveQuXCe3grfrCeco9UkmctVrebUu0e0Y/s=; b=iYGxWCaoyzyWXWSgqh5TpdrQjHjpwybBpTgbTwJuqgyK8cP2jukGZGOHwCYCm8oV6E/2DZ aHkGB/xDP8EId7j3aCq+HSH6SutUiTQPD7r8ASL/cVYHrDwLnNLLDmWYU1+1lFzckyn1yI VhP+/pgVyA5GXIv0tO8vIvPvvf7WrzmLDTwccoqthXc/x80s3sC5s4MBtthh3sLJ+ukFlW f+clpKw/R6hZxk84O3pf14R4OgrReft3JyXPCsRTl6LtERbtJYNN+g3ViMmBpJqAd7KnxU E21qZ52Z5KPTGDfbCOtsDqJQ4v7Nb02zzqhetxYaKCIUsuIbUmKjhmQXpCRusA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1744200297; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=LBtR6S8RUveQuXCe3grfrCeco9UkmctVrebUu0e0Y/s=; b=Yxt+dh9wXqJ7V2bpMLdDpCJNc9pVBPTBzoVzr5nAdAN9y1y7AnkwECvDT+h4Wkeuy+FS0e 7UiP/YXt7Jxx6vAA== From: "tip-bot2 for Borislav Petkov (AMD)" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: x86/urgent] Documentation/x86: Zap the subsection letters Cc: "Borislav Petkov (AMD)" , Ingo Molnar , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20250409111435.GEZ_ZWmz3_lkP8S9Lb@fat_crate.local> References: <20250409111435.GEZ_ZWmz3_lkP8S9Lb@fat_crate.local> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <174420029649.31282.6766699753807343972.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable The following commit has been merged into the x86/urgent branch of tip: Commit-ID: 254a6d14c9c952e8eae0fafd4fed3778721b948e Gitweb: https://git.kernel.org/tip/254a6d14c9c952e8eae0fafd4fed37787= 21b948e Author: Borislav Petkov (AMD) AuthorDate: Wed, 09 Apr 2025 13:14:35 +02:00 Committer: Ingo Molnar CommitterDate: Wed, 09 Apr 2025 13:56:52 +02:00 Documentation/x86: Zap the subsection letters The subsections already have numbering - no need for the letters too. Zap the latter. Signed-off-by: Borislav Petkov (AMD) Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20250409111435.GEZ_ZWmz3_lkP8S9Lb@fat_crate= .local --- Documentation/arch/x86/cpuinfo.rst | 51 ++++++++++++++++------------- 1 file changed, 29 insertions(+), 22 deletions(-) diff --git a/Documentation/arch/x86/cpuinfo.rst b/Documentation/arch/x86/cp= uinfo.rst index 7114f34..f80e2a5 100644 --- a/Documentation/arch/x86/cpuinfo.rst +++ b/Documentation/arch/x86/cpuinfo.rst @@ -79,8 +79,9 @@ feature flags. How are feature flags created? =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D =20 -a: Feature flags can be derived from the contents of CPUID leaves. ------------------------------------------------------------------- +Feature flags can be derived from the contents of CPUID leaves +-------------------------------------------------------------- + These feature definitions are organized mirroring the layout of CPUID leaves and grouped in words with offsets as mapped in enum cpuid_leafs in cpufeatures.h (see arch/x86/include/asm/cpufeatures.h for details). @@ -89,8 +90,9 @@ cpufeatures.h, and if it is detected at run time, the fla= gs will be displayed accordingly in /proc/cpuinfo. For example, the flag "avx2" comes from X86_FEATURE_AVX2 in cpufeatures.h. =20 -b: Flags can be from scattered CPUID-based features. ----------------------------------------------------- +Flags can be from scattered CPUID-based features +------------------------------------------------ + Hardware features enumerated in sparsely populated CPUID leaves get software-defined values. Still, CPUID needs to be queried to determine if a given feature is present. This is done in init_scattered_cpuid_featur= es(). @@ -104,8 +106,9 @@ has only one feature and would waste 31 bits of space i= n the x86_capability[] array. Since there is a struct cpuinfo_x86 for each possible CPU, the wast= ed memory is not trivial. =20 -c: Flags can be created synthetically under certain conditions for hardwar= e features. ---------------------------------------------------------------------------= ----------- +Flags can be created synthetically under certain conditions for hardware f= eatures +--------------------------------------------------------------------------= ------- + Examples of conditions include whether certain features are present in MSR_IA32_CORE_CAPS or specific CPU models are identified. If the needed conditions are met, the features are enabled by the set_cpu_cap or @@ -114,8 +117,8 @@ the feature X86_FEATURE_SPLIT_LOCK_DETECT will be enabl= ed and "split_lock_detect" will be displayed. The flag "ring3mwait" will be displayed only when running on INTEL_XEON_PHI_[KNL|KNM] processors. =20 -d: Flags can represent purely software features. ------------------------------------------------- +Flags can represent purely software features +-------------------------------------------- These flags do not represent hardware features. Instead, they represent a software feature implemented in the kernel. For example, Kernel Page Table Isolation is purely software feature and its feature flag X86_FEATURE_PTI = is @@ -130,8 +133,8 @@ x86_cap/bug_flags[] arrays in kernel/cpu/capflags.c. Th= e names in the resulting x86_cap/bug_flags[] are used to populate /proc/cpuinfo. The nami= ng of flags in the x86_cap/bug_flags[] are as follows: =20 -a: Flags do not appear by default in /proc/cpuinfo --------------------------------------------------- +Flags do not appear by default in /proc/cpuinfo +----------------------------------------------- =20 Feature flags are omitted by default from /proc/cpuinfo as it does not make sense for the feature to be exposed to userspace in most cases. For exampl= e, @@ -139,8 +142,8 @@ X86_FEATURE_ALWAYS is defined in cpufeatures.h but that= flag is an internal kernel feature used in the alternative runtime patching functionality. So = the flag does not appear in /proc/cpuinfo. =20 -b: Specify a flag name if absolutely needed -------------------------------------------- +Specify a flag name if absolutely needed +---------------------------------------- =20 If the comment on the line for the #define X86_FEATURE_* starts with a double-quote character (""), the string inside the double-quote characters @@ -155,25 +158,28 @@ shall override the new naming with the name already u= sed in /proc/cpuinfo. Flags are missing when one or more of these happen =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D =20 -a: The hardware does not enumerate support for it. --------------------------------------------------- +The hardware does not enumerate support for it +---------------------------------------------- + For example, when a new kernel is running on old hardware or the feature is not enabled by boot firmware. Even if the hardware is new, there might be a problem enabling the feature at run time, the flag will not be displayed. =20 -b: The kernel does not know about the flag. -------------------------------------------- +The kernel does not know about the flag +--------------------------------------- + For example, when an old kernel is running on new hardware. =20 -c: The kernel disabled support for it at compile-time. ------------------------------------------------------- +The kernel disabled support for it at compile-time +-------------------------------------------------- + For example, if 5-level-paging is not enabled when building (i.e., CONFIG_X86_5LEVEL is not selected) the flag "la57" will not show up [#f1]_. Even though the feature will still be detected via CPUID, the kernel disab= les it by clearing via setup_clear_cpu_cap(X86_FEATURE_LA57). =20 -d: The feature is disabled at boot-time. ----------------------------------------- +The feature is disabled at boot-time +------------------------------------ A feature can be disabled either using a command-line parameter or because it failed to be enabled. The command-line parameter clearcpuid=3D can be u= sed to disable features using the feature number as defined in @@ -186,8 +192,9 @@ disable specific features. The list of parameters inclu= des, but is not limited to, nofsgsbase, nosgx, noxsave, etc. 5-level paging can also be disabled u= sing "no5lvl". =20 -e: The feature was known to be non-functional. ----------------------------------------------- +The feature was known to be non-functional +------------------------------------------ + The feature was known to be non-functional because a dependency was missing at runtime. For example, AVX flags will not show up if XSAVE featu= re is disabled since they depend on XSAVE feature. Another example would be b= roken