From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (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 960FE37BE8F for ; Mon, 23 Mar 2026 22:04:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774303462; cv=none; b=IhnZy1ceCH5j6vRd6lVujy0JWNuW57Gr1QXLYrLVNT4ICBagZslA4YeCKg92UKbHw0pGtsdmID4YoLyZlqvNJKKIimiwWCxHNeavBnyQoLVEZD/Q99W7oc3cDeXAdQo0mI0htq/GkFEdMBUHdsqAD0ExxclMU2n+NUy/BL/Hckk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774303462; c=relaxed/simple; bh=sxoa3sdYvlfjFzyjt2aU0AhM5FQpXVySJNV93jcZdmk=; h=Date:From:To:CC:Subject:In-Reply-To:References:Message-ID: MIME-Version:Content-Type; b=ojSRTLZXImxfUKWSuSGW4tC6Lc0TLKsvAs1F+HNHh9JwF+tU3gKEQu0J17fK1nGnvXaZST87Gnx1w1c1Ms4F/kY661btI65XGxdSmbutd0vTVfhzZhz7Q5qVgp5gmfNgL/UP2wE9gxthmypKwfkJ20T7w7ju1Lo53R8xrk1f88w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=lpSmjJPg; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="lpSmjJPg" Received: from ehlo.thunderbird.net (c-76-133-66-138.hsd1.ca.comcast.net [76.133.66.138]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 62NM3dlI3290182 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Mon, 23 Mar 2026 15:03:40 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 62NM3dlI3290182 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2026022301; t=1774303420; bh=sxoa3sdYvlfjFzyjt2aU0AhM5FQpXVySJNV93jcZdmk=; h=Date:From:To:CC:Subject:In-Reply-To:References:From; b=lpSmjJPgva+h4UmbWfwSoLnAk2HxiuYbkuTOtu5LffIitLjzVyWP1vQq2NGn3gLla 2TM9lyTt4wcdko4J6B99vLqW4oLhP6NUz9onT/CQZk/GjzOp/VysFuK0uJLOOQo5cQ ms1fRsideUyvFB0KEXr6DR58k9r4np9PAn5JEatyWvnxQCf9zvncLilfQy1w/u1z36 ZrrFFdo7M+NmROjDq07zh7O2lbVBaXkk3iQ7Xa1QoC4aX3nOd5TVkActpmaYKshzqy 8jYiJtWiSrxYLYmXTF/1/jjs5+vUgFuibkoYjHNUykmZu8tJ7PTVbZjldLtjJyAfz5 i3IBFYmKIKu+g== Date: Mon, 23 Mar 2026 15:03:34 -0700 From: "H. Peter Anvin" To: Borislav Petkov CC: Maciej Wieczor-Retman , tglx@kernel.org, peterz@infradead.org, xin@zytor.com, maciej.wieczor-retman@intel.com, babu.moger@amd.com, chang.seok.bae@intel.com, sohil.mehta@intel.com, dave.hansen@linux.intel.com, jpoimboe@kernel.org, elena.reshetova@intel.com, pawan.kumar.gupta@linux.intel.com, ak@linux.intel.com, darwi@linutronix.de, mingo@redhat.com, x86@kernel.org, linux-kernel@vger.kernel.org Subject: =?US-ASCII?Q?Re=3A_=5BPATCH_v11_3/4=5D_x86/cpu=3A_Do_a_s?= =?US-ASCII?Q?anity_check_on_required_feature_bits?= User-Agent: K-9 Mail for Android In-Reply-To: <20260323215049.GGacG1uc-PQLp9DqWo@fat_crate.local> References: <7312c9f2feab8aea4612ed9a1841e8c22f5f69b1.1774008873.git.m.wieczorretman@pm.me> <20260323163145.GGacFq8WW0t2uqZm91@fat_crate.local> <207ba0a6-5ebc-465a-8d54-6e5a99622a72@zytor.com> <20260323191905.GDacGSKaG4rEU8O4NA@fat_crate.local> <20260323205841.GFacGpgZDBOCCG9Y5u@fat_crate.local> <20260323215049.GGacG1uc-PQLp9DqWo@fat_crate.local> Message-ID: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On March 23, 2026 2:50:49 PM PDT, Borislav Petkov wrote: >On Mon, Mar 23, 2026 at 02:40:47PM -0700, H=2E Peter Anvin wrote: >> I did: the PAE case, which was not hypothetical=2E I'm sure I can dig u= p more=2E > >So let's start our justification from this POV: we have use cases X and Y= and they >would profit from getting these warning checks about required features no= t >being set=2E > >I still am not persuaded that we want Linux to boot on those=2E Because t= hose >CPUs are clearly "out of whack" and they would work by pure luck=2E > >But I don't know anything about the particular snafus that happened there= =2E > >To take your example, the BIOS vendor disabled PAE=2E Do you really wanna= deal >with fixing that? I mean, what else is b0rked there=2E=2E=2E? > >So frankly, I'd turn that taint into a panic=2E > >Because this CPU sounds to me like an all-bets-are-off thing=2E > Yes, hence the tainting=2E The PAE case is historic, but it was a concrete example I had in my head w= here this issue You also of course mention BIOS settings and there are VMs = =2E=2E=2E