From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793532478; b=rha6pGlynO9MxNqBVdcJDaXoxubGcrqZuJrlY7rTeq3iDm6eleRJUMSbxprwO0OSxxKb jCQrMf0X4tOOo2fQHWX/irilxJCDJa/KUGTpcpEtLMEATfvY3Ax3xCh6k7RfiMmpjpvn/ kXermCCDs+9KLm/1qjGTgWXSNQYb6uFHmI33QnH21qiE30oFZ7qcMzLtwPS/igFWn3bF9 R99Ap+YTEyRySur29xBtrNpw5Xy+19cDzfyeb+bmDwgJMg2dIBjT6jHdV4kLNWv/DbdYI meFUJC5jItBVWLR7V/RHQurTR2KGSo3Uhp57+y4Z68rp7Twda3cq5adSS8/F67H1aPA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793532478; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=siqR+D9HkbI6+sWgtn1cpXSgsKhOnoez6zawNDWUpYc=; b=cOw1AaZ6bk2HNwyQhCHAaJoyAMs6VV3H8cpdbyc/CgiqABlhoOjHkdYSuTIdnJv404Uk 9lzPvVM3sjJNb7M8bOgg8it3llEOXTbDuW+MCRKEnY5eWAIB6/UpEuz5xU4Oxg0ZgiSIG jXCdf17SKNnnN7JODBecpsx/dOkyJmubksFStT0o69T+pkVhewThudfotX3af0/VaybEx TbU6A3BfQ22FugzZwtCkQV8s0eheTd0URDd9W9ohXKcfe/LwL5J5VxS2oMLvGt4aYlYKR dzCYTonNlJ8+tGZbJMfbmGyMNQUwzAg2kRaNI4cMUhiReSm/wQHFbXBvvGIbJ22TlJA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=cB1Hk1sN; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0C980606A324 for ; Sun, 1 Nov 2026 11:27:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=cB1Hk1sN Received: by smtp.kernel.org (Postfix) with ESMTPSA id ED8D21F000C1; Sun, 1 Nov 2026 11:27:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793532477; bh=siqR+D9HkbI6+sWgtn1cpXSgsKhOnoez6zawNDWUpYc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=cB1Hk1sNxBlDNzC+BygHOB0Weos2tKXuaBV7tar8GHJCQwSgp7IrGYkNyisex/DRq t7Li6T/8l0AKgO40Fa74Y2rf1MxMOkB8zgqocDos5g2HK/eYCUsX+natjhHWWftQBm gNb9g9xFCbHCfK5QLbTwAuhl0NlQR+08yqhhHJUFLv2wmP7p0r1ZEBi8Co4xzUc4uE bL4VPOSSbvEz6NvYiKJPexnRAJtX2ByTA17NccAaXfAxkTjqzrNcSF2eE6Mx/rUXBu 9UOW65ULWO9Tz+fWc0bFzyttc+kFbhFo14mwaYoWQk9QzEGULqH1fDwHwByRAlooYX +2zKpBltKmxZg== Message-ID: Date: Sun, 1 Nov 2026 12:27:54 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/3] x86: Make processor vendor selection available without EXPERT To: Borislav Petkov , Vincent Mailhol Cc: Thomas Gleixner , Ingo Molnar , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , linux-kernel@vger.kernel.org References: <20261031-processor_select_is_not_an_expert_feature-v1-0-6227bdbbe5a9@kernel.org> <20261031214351.GCauZhF1l6ENBfLKIS@fat_crate.local> From: Vincent Mailhol Content-Language: en-US Autocrypt: addr=mailhol@kernel.org; keydata= xjMEZluomRYJKwYBBAHaRw8BAQdAf+/PnQvy9LCWNSJLbhc+AOUsR2cNVonvxhDk/KcW7FvN JFZpbmNlbnQgTWFpbGhvbCA8bWFpbGhvbEBrZXJuZWwub3JnPsKZBBMWCgBBAhsDBQsJCAcC AiICBhUKCQgLAgQWAgMBAh4HAheAFiEE7Y9wBXTmfyDldOjiq1/riG27mcIFAmrTM8wFCR1O HxcACgkQq1/riG27mcJ2KAEAhG19xBSkjiA9dtatvq2WJnGaes4SUmY+LSn7dh1Lf7YBAIwB lsMMmigMTk3Qgwymg1nT+Z8z1Owc/TGtRlo4ZcwMzjgEZx4y8xIKKwYBBAGXVQEFAQEHQJrb YZzu0JG5w8gxE6EtQe6LmxKMqP6EyR33sA+BR9pLAwEIB8J+BBgWCgAmAhsMFiEE7Y9wBXTm fyDldOjiq1/riG27mcIFAmrTNKcFCRUFdT0ACgkQq1/riG27mcLEVwD/VmnQtTf6yhowaIFj AjUtwiyQz9ja4NRu9GOvz/pb2L8A/3QcADR0dcxADGsmOiBpN2M9KI7nqdNIq3VPM/3/5fcB In-Reply-To: <20261031214351.GCauZhF1l6ENBfLKIS@fat_crate.local> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 31/10/2026 at 22:43, Borislav Petkov wrote: > On Sat, Oct 31, 2026 at 08:51:48AM +0100, Vincent Mailhol wrote: >> Restricting a kernel build to a known CPU vendor currently requires >> enabling EXPERT. >> >> Make PROCESSOR_SELECT available without EXPERT. It remains disabled by >> default, preserving support for all applicable CPU vendors in existing >> configurations. > > What I am not seeing is git archeology about why it is behind EXPERT and > whether that reason is or is not valid anymore. PROCESSOR_SELECT was introduced in 2008 by commit 8d02c2110b3f ("x86: configuration options to compile out x86 CPU support code"). At that time, it was gated by CONFIG_EMBEDDED with space savings given as the main motivation. In the thread [1], Bodo pointed out that this wasn't specific to embedded systems but his comment didn't get any replies. Commit 6a108a14fa35 ("kconfig: rename CONFIG_EMBEDDED to CONFIG_EXPERT") then did a treewide renaming. The commit explains that EMBEDDED already covered nonstandard configurations beyond embedded systems but does not give a PROCESSOR_SELECT-specific rationale. Beyond Bodo's unanswered comment, I did not find further discussion of the relevance of PROCESSOR_SELECT for non-embedded machines or the Kconfig user experience. The main point I am raising in this series is how easily users should be able to disable all the features specific to CPU vendors they do not need. I think this aspect deserves further discussion. Finally, the size savings have changed since 2008. As reported in my tests, an AMD-only build reduces vmlinux.o size by 8.88%. What used to be a micro-optimization back then now has a much bigger impact. [1] https://lore.kernel.org/all/E1KRp7q-0001pd-61@be1.7eggert.dyndns.org/ Yours sincerely, Vincent Mailhol