From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f73.google.com (mail-pj1-f73.google.com [209.85.216.73]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DEF8F1F708F for ; Wed, 4 Dec 2024 15:31:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.73 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733326262; cv=none; b=Tmw+UUntsDhlp9Lx7pFI6/PUZmxqfniLBO+JPRWfVyhgWYG074jptFhR0H/UZCmfnssosIMfnm1OCgAtMPrSqMzOmxC7/pHmvOoHTxcPCaopGoF1kAbnQsKos2vI+kdxEpJw2Jp7IZ8Hg2ew+CkiKmDJbIKwT0DYmCSckXwm5DY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733326262; c=relaxed/simple; bh=raZSwCSoIxMAMxZedsY7kgc1gQPkh8K/6vkYq+qQ0yU=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=cUAxwhQ6lgirhy0MVyfZUod3rR6Q5SnuZQm1JO0fFpV9FmtQkeaBCDjmp6bgTVyJOMoa+m+O/3cHz/QRjpYl4mTmBevSzAYrrrxvy7aigCRpwb5yKD+VYZKHJL6l+PjqVW2A2NAoVZUrB58AwstuTwdT4dmsyRb3pQenf9eaK68= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=s7cfGAPq; arc=none smtp.client-ip=209.85.216.73 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="s7cfGAPq" Received: by mail-pj1-f73.google.com with SMTP id 98e67ed59e1d1-2e5efb04da7so6490093a91.0 for ; Wed, 04 Dec 2024 07:31:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1733326260; x=1733931060; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=LWzYXhh1XGle9PKP984gp5jQmjBdiOdHdzDrlgt7MZk=; b=s7cfGAPqPixORq7s40p3eeNZ/H1XR5cPKckVKg9m2ggNuD61U8uFHMGNSh5YYHOw10 PWLRT8ocbR8jRE7eFe8qEQHHCvtINmDWRtHDPVIT8ZRQf2lijLxqDnx6ctnNzl8w7ltd 5XKX+vMjqscW+ArK9+OzUgcr9T9YzWGXmvw1ymuRLiWJ7nsdvE1n+GXFWU3WTC8hL6z9 vG4S6lHJUkQdTKys0Qy4BrcXPZlT7+wcqKlyr618RWtSi3AFrSuhxewrwPA6fIMjigMK hLCupV5MSqWMJgG/O2IkIdW7D2a6fQcMMNadBY87dR3T9r2Xxus3VCMEhhT6b9r0V1fk k/lw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1733326260; x=1733931060; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=LWzYXhh1XGle9PKP984gp5jQmjBdiOdHdzDrlgt7MZk=; b=wdm6I2gVUTYC6WS6h0RqJ+ml5tpEhZ3ArEv718rj9lHIUtln5i1tCulIwdYvXI3Udl FBCDleVG8vQVWl6YbborxWtkowPCdTOyS4xSG+31UQ0FfB0TdU+sOVkFw2swBlvNJ66V Misp96UieeapqUM/qJxRg2uN5H9PYmJ7QpkX88TFbbUj4gm9MMmGClp0EUy8tBH7VEqY uTDvJHXer2lhCLA0YPrX+DJ+DcrRiBrD5//nToPm5bUe9uDZlX4WKSv2HGCSbAHKv0a3 7TQow1LY/lC9OHoOsS1orZToMTp73SFibD/c8eBHhndXlHIX6WYejBT2XLff9mAZqYIe mc0Q== X-Gm-Message-State: AOJu0Yz8+kKT4lW+MXem3OYho7uyQKnEN7vh7OBt12XfqAsZAAdFjPWD 4s2DkVWBCFM3nKKeRhj4YCPMWHe87hkCfH6x19ZlRNUxCoHCtuWYjI6fv1TqhaNHB7dJDvqZUJS BFA== X-Google-Smtp-Source: AGHT+IG8hKZnFRirR/ao2e8umiwaB/AV15nxqrbtp2UlNP2cgH4Q1y4HPfvHflLtOx0OwlnKrZjyoia9Lc8= X-Received: from pjj15.prod.google.com ([2002:a17:90b:554f:b0:2e5:5ffc:1c36]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:1a8e:b0:2ee:f550:3848 with SMTP id 98e67ed59e1d1-2ef011e3802mr8465345a91.5.1733326260234; Wed, 04 Dec 2024 07:31:00 -0800 (PST) Date: Wed, 4 Dec 2024 07:30:58 -0800 In-Reply-To: <20241204103042.1904639-12-arnd@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20241204103042.1904639-1-arnd@kernel.org> <20241204103042.1904639-12-arnd@kernel.org> Message-ID: Subject: Re: [PATCH 11/11] x86: drop 32-bit KVM host support From: Sean Christopherson To: Arnd Bergmann Cc: linux-kernel@vger.kernel.org, x86@kernel.org, Arnd Bergmann , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Linus Torvalds , Andy Shevchenko , Matthew Wilcox , Davide Ciminaghi , Paolo Bonzini , kvm@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Wed, Dec 04, 2024, 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 release just before their > 64-bit counterparts. > > Using KVM as a host on a 64-bit CPU using a 32-bit kernel generally > works fine, but is rather pointless since 64-bit kernels are much better > supported and deal better with the memory requirements of VM guests. > > Drop all the 32-bit-only portions and the "#ifdef CONFIG_X86_64" checks > of the x86 KVM code and add a Kconfig dependency to only allow building > this on 64-bit kernels. While 32-bit KVM doesn't need to be a thing for x86 usage, Paolo expressed concerns that dropping 32-bit support on x86 would cause general 32-bit KVM support to bitrot horribly. 32-bit x86 doesn't get much testing, but I do at least boot VMs with it on a semi-regular basis. I don't think we can say the same for other architectures with 32-bit variants. PPC apparently still has 32-bit users[1][2], and 32-bit RISC-V is a thing, so I think we're stuck with 32-bit x86 for the time being. :-( [1] https://lore.kernel.org/all/87zg4aveow.fsf@mail.lhotse [2] https://lore.kernel.org/all/fc43f9eb-a60f-5c4a-a694-83029234a9c4@xenosoft.de