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 EF266378817 for ; Mon, 30 Mar 2026 23:57:07 +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=1774915029; cv=none; b=cQ8TT5VxJBQaB5C0+0IoLiqwSB2GauYxlBmn6p2qbgV10nOIlyEKNPtrwuhOkmYnM5gkAvCOHiQv/d+c3610IZbgKw3N1ekpu+gASYWvoE8DqT+dGzOTipVLkEx/I2mLZp0GJqYT21ma9JMplTaC3viQoXd7YAnzvTT+bTUoh8g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774915029; c=relaxed/simple; bh=Y/qAYVN9BWAiH+SilK/xX1G5D0o70d47vxAMSoBrGzc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=nmxWI3C4ZJYat3w72grmFj3ZTKyTomlc4IJ62cwgeaL7YmGRn2UzcMnTvySVpm3nlLtND7caRKA8Y8JF147BkiSr6n3YOUvZ+HIt5CRpbkrVEi5ZIevlkDxZ/T1tRG6XOt7SkeVUhTTn27f/hhV1lY8hIWPVKMJ8t3BWLZRn91U= 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=a6CYfMXl; 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="a6CYfMXl" Received: from [172.27.2.41] (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 62UNeRD02856263 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Mon, 30 Mar 2026 16:40:28 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 62UNeRD02856263 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2026032601; t=1774914029; bh=J0ybCh4fD3JQ1o9nDZzWQZy8AFc5EZJ7ygavS0XD39Y=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=a6CYfMXln/mVfGFOXN5pYf4RdXI1FGpzaeiIl+FYLieqZRJGJnNeRJ+bGfVRb/j/u 6H1mw8IN3TsINanNQxfeQ7JnEpWBIfkcbh4Nbx2w7tw2ZZZMZaETyS8gXnRhBtiYSY lpmJCOxX7t55UzAqWoO3HGwXCDyeHXYE9pQGWT6qh8E/JCfIIkjqBYxfSogTG6zUPZ buP/cQTf1beOZ9D0WTDLmh+lUp//fpcX+3HxqqCoYSdrKCVWXR3ljo3ebnvilMf/Qr rWZjzGgw+SeFjDblmnotiSLii0p2AhdCfjXFxIJAGrW6S+QR6EaN9ENzn+SmuskhV1 TTqH4vk3mAiFw== Message-ID: <872d030a-5080-4dfb-bb3a-2aacc915f737@zytor.com> Date: Mon, 30 Mar 2026 16:40:22 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v12 0/4] x86: Capability bits fix and required bits sanity check To: Andi Kleen , Maciej Wieczor-Retman Cc: bp@alien8.de, dave.hansen@linux.intel.com, xin@zytor.com, chang.seok.bae@intel.com, mingo@redhat.com, elena.reshetova@intel.com, maciej.wieczor-retman@intel.com, babu.moger@amd.com, sohil.mehta@intel.com, pawan.kumar.gupta@linux.intel.com, pmladek@suse.com, nik.borisov@suse.com, ptesarik@suse.com, darwi@linutronix.de, tglx@kernel.org, peterz@infradead.org, jpoimboe@kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org References: Content-Language: en-US, sv-SE From: "H. Peter Anvin" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2026-03-29 23:11, Andi Kleen wrote: > > I'm not sure what the point of this check is. Obviously the kernel cannot > handle it, short of refusing to boot which would be far too drastic. > > And if it's just for having something in the kernel log, who would look > for this? Any possible symptoms from a bogus cpuid will be far > disconnected from that particular log location. > > Further, there's also no evidence that it is a real practical problem. > If anything it could likely only come from rogue VMMs, but these don't > seem to be common. But VMMs normally don't really disable ISA, so even if the > CPUID is inconsistent things will still likely work because the actual > instructions are fine. > That's the main case; "it seems to work but if it breaks you get to keep both pieces" -- i.e. the EXACT meaning of TAINT_CPU_OUT_OF_SPEC. See my other posts on this thread. > Assuming it was a real problem, you could just do it in a user program, why > put it into the kernel and waste everyone's memory? (this cannot be > initcode due to hotplug) > > Also it seems to violate Steinbach's system programing maxim > (never check for something you don't know how to handle) You *do* realize that is sarcasm, right? -hpa