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 4231B1D6187; Thu, 25 Sep 2025 15:33:19 +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=1758814402; cv=none; b=PT66vZXrZ/iUgGVBRhx/PWq4b8XilVM7VwpFtIu/G1pC9Lb0N5RRyHuywiW2JuXsKAzUbwfsXnD6F+5HMAOWGHiUZDvsm3p7XIcIrZ8/psuAtEagE+lMi4ZZeB5qbf3ni8PHRRF7d8mEUUpxS7gPt2riWCQ+en0ayuBYO580d/Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758814402; c=relaxed/simple; bh=u5FAkVs1d2yn2V+vcAWfPQaluNSH3+uZoP8oWWENrP8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=IbUmVP2GDio8+0xjxKVKFAG7mljCmwtZUXV2V3wC3RgxTJYFb9+Hy97+n4MJXIC++7HwVO9Oh9O3LZyNlrRFF+m+XzUtp47fhJ/kOd5mJVO/tCFZQ7uFXDr/hmoqWqdHcbgJ07gGfvuP36ICcbdmjdSOMDAKqKWY81KjlUlHPpk= 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=XN7IDCL2; 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="XN7IDCL2" Received: from [IPV6:2601:646:8081:9484:60d0:6c9:beea:16a] ([IPv6:2601:646:8081:9484:60d0:6c9:beea:16a]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 58PFWQ7T2493900 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Thu, 25 Sep 2025 08:32:27 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 58PFWQ7T2493900 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2025092201; t=1758814349; bh=AlBarqxfhsKUEiXxrH663bEYPMkBt9GFIKZMwmsouDE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=XN7IDCL2hY74mA4XAqYEpQlWM22WhzIkHQDMT09Fa7KGN2qfZXMZH8A5+62nxAlYK hRT5jjh5KjF/gSUrUk81P2hu67RN0xhpMV05N3g8+TqWEHSVBCo5Lkyc/2RXaaCj5W WHTZhiQd8oCnOiRaueELO3jym5VFYB3Kda676ngVklxmqfoi+6ItqxjzP9br9U82U5 LZ/EipCl9W8Em9a1jMStFuIREedWydmfnLgBLYsdklw4Gbtd3YwsVA/8RjGQUgifRu ufhw0YVOOxe1RXNMeE5ulR4YF+0nO2qqCdlXDiy5WK5175xuFfwrerCAa2tnhEZWkW PsBStTLa0kl5w== Message-ID: <113902a5-a635-4d21-8192-8c6d482e88bf@zytor.com> Date: Thu, 25 Sep 2025 08:32:21 -0700 Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [External] Re: [RFC 0/5] parker: PARtitioned KERnel To: Fam Zheng Cc: fam@euphon.net, Dave Hansen , linux-kernel@vger.kernel.org, Lukasz Luba , linyongting@bytedance.com, songmuchun@bytedance.com, satish.kumar@bytedance.com, Borislav Petkov , Thomas Gleixner , yuanzhu@bytedance.com, Ingo Molnar , Daniel Lezcano , Zhang Rui , x86@kernel.org, liangma@bytedance.com, Dave Hansen , "Rafael J. Wysocki" , guojinhui.liam@bytedance.com, linux-pm@vger.kernel.org, Thom Hughes References: <20250923153146.365015-1-fam.zheng@bytedance.com> <40419dea-666e-4a8d-97a7-fa571d7122f4@intel.com> <585D086B-733C-4274-B274-794F360E8E33@zytor.com> 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 2025-09-25 00:26, Fam Zheng wrote: >> From: "H. Peter Anvin" >> The difference is that this is highly invasive to the OS, which affects developers and users not wanting this feature. > > Yeah that makes sense, thanks for clarifying. By having a hypervisor > at least in early boot of secondary kernels, we don't need to patch > device enumeration etc. In the kernel code. > > Once the kernel is up, it can be then promoted to run directly on bare > metal, so zero performance overhead. Realistically you would remain in the hypervisor, but nothing or almost nothing will trap into the hypervisor, so again, zero or negligible performance overhead. You also *can* put some isolation or protection features in the low-level hypervisor. The important thing here is that the maintenance burden *and* the policy choices fall on the users of the feature, and as the upstream maintainers cannot and thus will not test this use case, it is likely to break on a regular basis. This is basically "paravirt_ops all over again." There are very good reasons we are trying to get rid of them. -hpa