From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 7D8321799F for ; Sat, 16 Mar 2024 21:37:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710625032; cv=none; b=e/4n0Z8OIyWqGOxFV8iH/xnAPGX3Bmuc3IaZ5YJaCZm/CtnL5pCXbPRZjDH9X6oxF2XaIBwo7+/N6eY4v5jyvpLRoJgWLoZrej/S8/I8ZY/ceWUUlCK/EFMo+Uh1Ks6Pfs8ucE63O1rLqOyfFp0aE4ZOyQ7yLz5OUKPXw4zTB44= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710625032; c=relaxed/simple; bh=GKKge2ecLnpGrZsiljqV2+mUEsMSfr3X5lirRlPQE+k=; h=MIME-Version:Message-Id:In-Reply-To:References:Date:From:To:Cc: Subject:Content-Type; b=ogSmR9o9kTCPT5eAm8QXWT9jGiIUgeyhocTZgJ9GOmLINJih15V3OeJmqFz/HDkSaPpHv0CpYndrign3f2hWyNhu33yO7dMxhB7jMqnlo7mMpesKRVM5Cx30YBPnVqEAtSuIlcPH75T2Oda4f93WA3aKzLeJq0k1T95+st7Fk/0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Kl4fgSWF; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Kl4fgSWF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D051CC43390 for ; Sat, 16 Mar 2024 21:37:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1710625032; bh=GKKge2ecLnpGrZsiljqV2+mUEsMSfr3X5lirRlPQE+k=; h=In-Reply-To:References:Date:From:To:Cc:Subject:From; b=Kl4fgSWFgWtaVAOeHm1HAn//iH9iEyrNUF5aUPW6UOF1jIDY5CtIEqD1IYHKfgTdP pR6hN95eyokzTS0ojBfdov1NBid0Ni3N8w00NZvrxFCb3XvOVMbtHHFNyKrvfYUy2N 05lJRMVxypa1q7gfNzrLr8EyU6oBxVJCZRXSuxEHwuMAKeICQOqBESuOo+qzUiWgJ1 Eg6TkM2ZyikbJrvG6TkbB2ZmTWmUQs4Rtni8JXoHo9CE3wE8H0tZl0/et6sGgfctzO fwzipZoNv3676sIwo8GmNiApnTAa22L5Rj/EnFhqj1H+E0lXTEj3yknPWETVdo2KJF PGGXoRMpxqaUw== Received: from compute5.internal (compute5.nyi.internal [10.202.2.45]) by mailfauth.nyi.internal (Postfix) with ESMTP id C94B11200068; Sat, 16 Mar 2024 17:37:10 -0400 (EDT) Received: from imap51 ([10.202.2.101]) by compute5.internal (MEProxy); Sat, 16 Mar 2024 17:37:10 -0400 X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvledrkedvgdduvdejucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhepofgfggfkjghffffhvfevufgtsehttdertderredtnecuhfhrohhmpedftehr nhguuceuvghrghhmrghnnhdfuceorghrnhgusehkvghrnhgvlhdrohhrgheqnecuggftrf grthhtvghrnhepleevgfduieehfeeltdettdfhfffgkedugeeklefftdeivdfgveeiteet keehffevnecuffhomhgrihhnpehkvghrnhgvlhdrohhrghenucevlhhushhtvghrufhiii gvpedtnecurfgrrhgrmhepmhgrihhlfhhrohhmpegrrhhnugdomhgvshhmthhprghuthhh phgvrhhsohhnrghlihhthidquddvkeehudejtddvgedqvdekjedttddvieegqdgrrhhnug eppehkvghrnhgvlhdrohhrghesrghrnhgusgdruggv X-ME-Proxy: Feedback-ID: i36794607:Fastmail Received: by mailuser.nyi.internal (Postfix, from userid 501) id 365F2B6008D; Sat, 16 Mar 2024 17:37:10 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface User-Agent: Cyrus-JMAP/3.11.0-alpha0-300-gdee1775a43-fm-20240315.001-gdee1775a Precedence: bulk X-Mailing-List: linux-sparse@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: In-Reply-To: References: <20240303235029.555787150@linutronix.de> <20240304005104.622511517@linutronix.de> <87y1ajjsv9.ffs@tglx> <87o7bfjeae.ffs@tglx> <877ci3j80k.ffs@tglx> Date: Sat, 16 Mar 2024 22:34:55 +0100 From: "Arnd Bergmann" To: "Linus Torvalds" , "Thomas Gleixner" Cc: "Guenter Roeck" , LKML , x86@kernel.org, "Uros Bizjak" , linux-sparse@vger.kernel.org, "kernel test robot" , oe-kbuild-all@lists.linux.dev Subject: Re: [patch 5/9] x86: Cure per CPU madness on UP Content-Type: text/plain On Sat, Mar 16, 2024, at 02:23, Linus Torvalds wrote: > On Fri, 15 Mar 2024 at 18:11, Thomas Gleixner wrote: >> >> You wish. We still support 486 and some of the still produced 486 clones >> do not have a local APIC. > > Ouch. I was _sure_ we had dropped i486 support too due to cmpxchg8b. > > But apparently that was just a discussion, and my wishful thinking, > and we never actually followed through. Maciej Rozycki still cares about i486 type hardware, and he was asking for it to be kept around in the thread following [1] I think the best suggestion at the time was to make cmpxchg8b a compile-time feature and I had expected Maciej to follow up with a patch for that, but this never happend, and nobody sent a patch to remove support 486 and the early 586 clones either. I saw recently that there are still distros that advertise 486 support on modern kernels: Tiny Core Linux and Damn Small Linux. Both ship with a 486 SMP kernel but fail to boot on qemu unless an APIC is enabled (DSL also requires i686 or higher to run userspace). Arnd [1] https://lore.kernel.org/all/20220815071332.627393-9-yuzhao@google.com/