From nobody Mon Nov 25 01:38:30 2024 Received: from mail.alien8.de (mail.alien8.de [65.109.113.108]) (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 8820A19994A; Thu, 31 Oct 2024 10:34:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=65.109.113.108 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730370876; cv=none; b=sagRHIKSepmQ0ksJyTHuOTIOPyKnt6u32P/nmSQE71f/sBiDKZSWtV/njHEizf/jdAIvmguObooChn/Up812nBYGXbl5lU32pzY7pQzNy2M3kHWpC8EMTDgeS7ZCk7AQvOOoQ6AaXjvBpKw1BTKu1ZxRBhbg99HjWi/rPmqTq/U= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730370876; c=relaxed/simple; bh=TPbtUoJ+jGDTtJ0ySfxGn2crD4a9xAZ2hYxDO2co/Ac=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=LQBFrb8c6Lz4URKjBMajecVWzcPIl/qrE5rwDkl0FiHFcE+7C/QGdyJtHawt8ZerARR57irffNBA0ta55VIXHp48eOzlxB7MORd4z3KF+MJgPZkUFbj/48vXkpAsvxw/4luK6rmkPrz0hAh1oL6PqwAPr39mCPcPcXLrRoCoQ1g= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=alien8.de; spf=pass smtp.mailfrom=alien8.de; dkim=pass (4096-bit key) header.d=alien8.de header.i=@alien8.de header.b=VN6hHEP3; arc=none smtp.client-ip=65.109.113.108 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=alien8.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=alien8.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (4096-bit key) header.d=alien8.de header.i=@alien8.de header.b="VN6hHEP3" Received: from localhost (localhost.localdomain [127.0.0.1]) by mail.alien8.de (SuperMail on ZX Spectrum 128k) with ESMTP id 12D0740E0219; Thu, 31 Oct 2024 10:34:32 +0000 (UTC) X-Virus-Scanned: Debian amavisd-new at mail.alien8.de Authentication-Results: mail.alien8.de (amavisd-new); dkim=pass (4096-bit key) header.d=alien8.de Received: from mail.alien8.de ([127.0.0.1]) by localhost (mail.alien8.de [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id 9H39GjSMgIyd; Thu, 31 Oct 2024 10:34:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=alien8; t=1730370867; bh=L+YfhXYMp9fc+q1eUkGrYH2j5uqrfhIaFjnfYZBfX8M=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=VN6hHEP3RqRkVpvGO7kZl0b/W75I3QEmvBPAKGq1DMQYIKriDw24cQf8h87mcUyxq ZxTdF38JplhZI48OBNcmCupfl+UEzKUn4wtXavDLvCFliGkyRWr54Nj/t2qNVHXCiE jpO4PRKzIrbXfPRHWQLPOjcsZzX649mGv+wjKGA3pqGpnebZpLEgXhTDGgPhzwPRu9 PxvKcHknCzeUrT/eCKJ1RRFWKB24tWq06oMsYPDPoS9xb7Uo49mqZqV0IAc/Fd44jh JihqF1cRwE1+IGWMApO0wVdc80FCY5CIKasgmvzaEFF4ZAQuK0ECYZ24McYHfccMzw 5oMbqYp3FlXzJHPGnxoEuOp+DgqYEapS+ihxdvB2I7f9iQOrFQtIL/2QJ7SOGAGLfi vGad4GR6y5kO0Qmwd27cwKaigOHNtvjoCurpy93UOrLnvBx+EZ7FQYtKNDbiOv6LKu /mhCTJcB9NfvBWbuq37VKGPPRivPcvsbg7kT0BlHlyP5thc25DxBqIH7XRm+gr6eZU DgOX8MRc8ud2qxP6G/UmjbKzCAPGWBNcWA/JyJqRFIY2BLnW+2Hto/lhSs8IYqwWpI Qc4icAwGb9yMgsq3ozBWvz/s4cQuL2URvj9BHj8v3mHalQJF/hr1/MpOWVU0KNRWmp 8U6ialZU3K4qvyODeGbfxU+I= Received: from zn.tnic (p5de8e8eb.dip0.t-ipconnect.de [93.232.232.235]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature ECDSA (P-256) server-digest SHA256) (No client certificate requested) by mail.alien8.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id AE8F940E015F; Thu, 31 Oct 2024 10:34:02 +0000 (UTC) Date: Thu, 31 Oct 2024 11:34:01 +0100 From: Borislav Petkov To: Sohil Mehta Cc: Yazen Ghannam , "Luck, Tony" , Andy Whitcroft , Joe Perches , "linux-edac@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , "avadhut.naik@amd.com" , "john.allen@amd.com" , "mario.limonciello@amd.com" , "bhelgaas@google.com" , "Shyam-sundar.S-k@amd.com" , "richard.gong@amd.com" , "jdelvare@suse.com" , "linux@roeck-us.net" , "clemens@ladisch.de" , "hdegoede@redhat.com" , "ilpo.jarvinen@linux.intel.com" , "linux-pci@vger.kernel.org" , "linux-hwmon@vger.kernel.org" , "platform-driver-x86@vger.kernel.org" , "naveenkrishna.chatradhi@amd.com" , "carlos.bilbao.osdev@gmail.com" Subject: [PATCH] x86/cpufeature: Document cpu_feature_enabled() as the default to use Message-ID: <20241031103401.GBZyNdGQ-ZyXKyzC_z@fat_crate.local> References: <20241023172150.659002-1-yazen.ghannam@amd.com> <20241023172150.659002-4-yazen.ghannam@amd.com> <20241025155830.GQZxvAJkJnfLfNpSRx@fat_crate.local> <20241029143928.GA1011322@yaz-khff2.amd.com> <20241029150847.GLZyD6f-Hk6pRTEt2c@fat_crate.local> <20241030142138.GA1304646@yaz-khff2.amd.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: "Borislav Petkov (AMD)" cpu_feature_enabled() should be used in most cases when CPU feature support needs to be tested in code. Document that. Reported-by: Sohil Mehta Signed-off-by: Borislav Petkov (AMD) Acked-by: Dave Hansen Reviewed-by: Sohil Mehta --- arch/x86/include/asm/cpufeature.h | 18 ++++++------------ 1 file changed, 6 insertions(+), 12 deletions(-) diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufe= ature.h index 0b9611da6c53..de1ad09fe8d7 100644 --- a/arch/x86/include/asm/cpufeature.h +++ b/arch/x86/include/asm/cpufeature.h @@ -132,11 +132,12 @@ extern const char * const x86_bug_flags[NBUGINTS*32]; x86_this_cpu_test_bit(bit, cpu_info.x86_capability)) =20 /* - * This macro is for detection of features which need kernel - * infrastructure to be used. It may *not* directly test the CPU - * itself. Use the cpu_has() family if you want true runtime - * testing of CPU features, like in hypervisor code where you are - * supporting a possible guest feature where host support for it + * This is the default CPU features testing macro to use in code. + * + * It is for detection of features which need kernel infrastructure to be + * used. It may *not* directly test the CPU itself. Use the cpu_has() fa= mily + * if you want true runtime testing of CPU features, like in hypervisor co= de + * where you are supporting a possible guest feature where host support fo= r it * is not relevant. */ #define cpu_feature_enabled(bit) \ @@ -161,13 +162,6 @@ extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsig= ned int bit); #define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit) =20 /* - * Static testing of CPU features. Used the same as boot_cpu_has(). It - * statically patches the target code for additional performance. Use - * static_cpu_has() only in fast paths, where every cycle counts. Which - * means that the boot_cpu_has() variant is already fast enough for the - * majority of cases and you should stick to using it as it is generally - * only two instructions: a RIP-relative MOV and a TEST. - * * Do not use an "m" constraint for [cap_byte] here: gcc doesn't know * that this is only used on a fallback path and will sometimes cause * it to manifest the address of boot_cpu_data in a register, fouling --=20 2.43.0 --=20 Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette