From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from fhigh-b6-smtp.messagingengine.com (fhigh-b6-smtp.messagingengine.com [202.12.124.157]) (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 ABBF51B21A2; Fri, 13 Dec 2024 09:22:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=202.12.124.157 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734081776; cv=none; b=skcpJEK6AHsKiDaVmJ4r4oXFbAuzR/UoADLgmS4GC7bygkUwwo5TAbbt8pUN94o7KOEoOLqs/TrxQxglJimhWgxpwIhETOU5qnUzceM6Fi8wRA0XacuNAjegeAogH+W2p4qCRbVAsQWWHF00aL8rTPyfpSoPxPhX4kqnzijqVIQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734081776; c=relaxed/simple; bh=l7QiCILD+TyAYh5PJNEJ39zLrVWBIrPnLOAuB2a5WaQ=; h=MIME-Version:Date:From:To:Cc:Message-Id:In-Reply-To:References: Subject:Content-Type; b=ByMb+bcFnv+fBw3sju0ocxvSwGS+kOgCAA1npeT+dCbI5cFNdN3VPnz/HoC63+beOGL7f3/+Ftv3ppOyYYapz+bGmLOXYKvEo8wjzPtgy1r9tLNvf2AMwn+eFqONwOjJThw+QIiw1iG9MoI6gR/Tf+OV1XxKKbJx4uj8UPurjwY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arndb.de; spf=pass smtp.mailfrom=arndb.de; dkim=pass (2048-bit key) header.d=arndb.de header.i=@arndb.de header.b=jPrxzkDW; dkim=pass (2048-bit key) header.d=messagingengine.com header.i=@messagingengine.com header.b=O3J2GfBs; arc=none smtp.client-ip=202.12.124.157 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arndb.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arndb.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=arndb.de header.i=@arndb.de header.b="jPrxzkDW"; dkim=pass (2048-bit key) header.d=messagingengine.com header.i=@messagingengine.com header.b="O3J2GfBs" Received: from phl-compute-10.internal (phl-compute-10.phl.internal [10.202.2.50]) by mailfhigh.stl.internal (Postfix) with ESMTP id B0E6725401EB; Fri, 13 Dec 2024 04:22:51 -0500 (EST) Received: from phl-imap-11 ([10.202.2.101]) by phl-compute-10.internal (MEProxy); Fri, 13 Dec 2024 04:22:52 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=arndb.de; h=cc :cc:content-transfer-encoding:content-type:content-type:date :date:from:from:in-reply-to:in-reply-to:message-id:mime-version :references:reply-to:subject:subject:to:to; s=fm1; t=1734081771; x=1734168171; bh=Suh2qqmp5LswXS6UM/NIeYadyUDj4ZrAq9xKXIGb2h0=; b= jPrxzkDWUl3aZHiWpcBoRvsXR2+XkpZRfhXJtHWInIubTyhL2qirmziXdiwbVByj 37KmlWdS8nGgBphp0T19RTCsNtRKK+hLRhyZpXD7xqz8q0ZX+2Gv8ZcdCio9/P7d 9RZJ2DxPVvlO1ktsiRfJwaosVD01tZtpnb7T+F/dLIz4Mh0ngwfJbQMc5kJ+rov2 +fijSthBoEwYko7qCCSeafPMNm0jQGZ+XNG43SKu+JiZf+aGCDLGCf5CbN8kC8ti oyzNPKT0z1S0OvW8KSruiJtj6cTUH9YgN/5cQYmiDs1wyaWOMtpcUTQ6INLHCRI9 aLXdn8s6LFtONQ3O9taeJQ== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:cc:content-transfer-encoding :content-type:content-type:date:date:feedback-id:feedback-id :from:from:in-reply-to:in-reply-to:message-id:mime-version :references:reply-to:subject:subject:to:to:x-me-proxy :x-me-sender:x-me-sender:x-sasl-enc; s=fm1; t=1734081771; x= 1734168171; bh=Suh2qqmp5LswXS6UM/NIeYadyUDj4ZrAq9xKXIGb2h0=; b=O 3J2GfBsFQXPk/CS3lrNw/2c+Fh6DQZ3psgwQDwf/B/6wK2En1fq1Aypf7BDPFEHb L022F8LfZsLo02faH1m7Gj5aWDvJHLoUHsnWn8CItk8UKD9ERyN7XZZMWJv/24CL ig86MxOlBgbJYB+LK4bYnv6lXm61XPjezwZfsyTZBcBLduSsRnT74mpaACIxkebW QebqzGVTbgK0hZ8Uio+sjmBkdo4uwS9Oa+bcXI9uzKBoz357j0a1iDtn48i07eEU mmPj9VOStcKN635SJp6XTHbbGJrT42uKf0AqZcD5LpbeIQgnJ9Q3ra/F4rr9Tb44 jKlXoc5F7QIb04fEYoAUw== X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeefuddrkeejgddtfecutefuodetggdotefrodftvf curfhrohhfihhlvgemucfhrghsthforghilhdpggftfghnshhusghstghrihgsvgdpuffr tefokffrpgfnqfghnecuuegrihhlohhuthemuceftddtnecusecvtfgvtghiphhivghnth hsucdlqddutddtmdenucfjughrpefoggffhffvvefkjghfufgtgfesthejredtredttden ucfhrhhomhepfdetrhhnugcuuegvrhhgmhgrnhhnfdcuoegrrhhnugesrghrnhgusgdrug gvqeenucggtffrrghtthgvrhhnpeefhfehteffuddvgfeigefhjeetvdekteekjeefkeek leffjeetvedvgefhhfeihfenucffohhmrghinhepkhgvrhhnvghlrdhorhhgnecuvehluh hsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrhhomheprghrnhgusegrrhhn uggsrdguvgdpnhgspghrtghpthhtohepfeegpdhmohguvgepshhmthhpohhuthdprhgtph htthhopegsphesrghlihgvnhekrdguvgdprhgtphhtthhopehtshgsohhgvghnugesrghl phhhrgdrfhhrrghnkhgvnhdruggvpdhrtghpthhtohepghhrrghfsegrmhgriihonhdrtg homhdprhgtphhtthhopegrthhishhhphesrghtihhshhhprghtrhgrrdhorhhgpdhrtghp thhtoheprghnuhhpsegsrhgrihhnfhgruhhlthdrohhrghdprhgtphhtthhopegthhhrih hsthhophhhvgdrlhgvrhhohiestghsghhrohhuphdrvghupdhrtghpthhtohepphgrlhhm vghrsegurggssggvlhhtrdgtohhmpdhrtghpthhtoheprghouhesvggvtghsrdgsvghrkh gvlhgvhidrvgguuhdprhgtphhtthhopehmphgvsegvlhhlvghrmhgrnhdrihgurdgruh X-ME-Proxy: Feedback-ID: i56a14606:Fastmail Received: by mailuser.phl.internal (Postfix, from userid 501) id 02ED32220072; Fri, 13 Dec 2024 04:22:48 -0500 (EST) X-Mailer: MessagingEngine.com Webmail Interface Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Fri, 13 Dec 2024 10:22:28 +0100 From: "Arnd Bergmann" To: "Paolo Bonzini" , "Arnd Bergmann" , kvm@vger.kernel.org Cc: "Thomas Bogendoerfer" , "Huacai Chen" , "Jiaxun Yang" , "Michael Ellerman" , "Nicholas Piggin" , "Christophe Leroy" , "Naveen N Rao" , "Madhavan Srinivasan" , "Alexander Graf" , "Crystal Wood" , "Anup Patel" , "Atish Patra" , "Paul Walmsley" , "Palmer Dabbelt" , "Albert Ou" , "Sean Christopherson" , "Thomas Gleixner" , "Ingo Molnar" , "Borislav Petkov" , "Dave Hansen" , x86@kernel.org, "H. Peter Anvin" , "Vitaly Kuznetsov" , "David Woodhouse" , "Paul Durrant" , "Marc Zyngier" , linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org Message-Id: <062f7269-580e-4008-904a-919ca0bda482@app.fastmail.com> In-Reply-To: <6bc05f3c-f473-480d-b9a2-c8cd3c80a66c@redhat.com> References: <20241212125516.467123-1-arnd@kernel.org> <20241212125516.467123-6-arnd@kernel.org> <6bc05f3c-f473-480d-b9a2-c8cd3c80a66c@redhat.com> Subject: Re: [RFC 5/5] x86: kvm drop 32-bit host support Content-Type: text/plain Content-Transfer-Encoding: 7bit >n Thu, Dec 12, 2024, at 17:27, Paolo Bonzini wrote: > On 12/12/24 13:55, Arnd Bergmann wrote: >> From: Arnd Bergmann >> >> There are very few 32-bit machines that support KVM, the main exceptions >> are the "Yonah" Generation Xeon-LV and Core Duo from 2006 and the Atom >> Z5xx "Silverthorne" from 2008 that were all released just before their >> 64-bit counterparts. > > Unlike other architectures where you can't run a "short bitness" kernel > at all, or 32-bit systems require hardware enablement that simply does > not exist, the x86 situation is a bit different: 32-bit KVM would not be > used on 32-bit processors, but on 64-bit kernels running 32-bit kernels; > presumably on a machine with 4 or 8 GB of memory, above which you're > hurting yourself even more, and for smaller guests where the limitations > in userspace address space size don't matter. > > Apart from a bunch of CONFIG_X86_64 conditionals, the main issue that > KVM has with 32-bit x86 is that they cannot read/write a PTE atomically > (i.e. without tearing) and therefore they can't use the newer and more > scalable page table management code. So no objections from me for > removing this support, but the justification should be the truth, i.e. > developers don't care enough. Right, I should have updated the description based on the comments for the first version, especially after separating it from the patches that make it harder to run 32-bit kernels on 64-bit hardware. I've updated the changelog now to x86: kvm drop 32-bit host support There are very few 32-bit machines that support KVM, the main exceptions are the "Yonah" Generation Xeon-LV and Core Duo from 2006 and the Atom Z5xx "Silverthorne" from 2008 that were all released just before their 64-bit counterparts. The main usecase for KVM in x86-32 kernels these days is to verify that 32-bit KVM is still working, by running it on 64-bit hardware. With KVM support on other 32-bit architectures going away, and x86-32 kernels on 64-bit hardware becoming more limited in available RAM, this usecase becomes much less interesting. Remove this support to make KVM exclusive to 64-bit hosts on all architectures, and stop testing 32-bit host mode. Link: https://lore.kernel.org/all/Z1B1phcpbiYWLgCD@google.com/ Signed-off-by: Arnd Bergmann which assumes that we end up going ahead with the powerpc patches. Does that work for you? Arnd