From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EA763C04A95 for ; Wed, 28 Sep 2022 17:44:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234651AbiI1Rod (ORCPT ); Wed, 28 Sep 2022 13:44:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51466 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234536AbiI1Rob (ORCPT ); Wed, 28 Sep 2022 13:44:31 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4555519C37 for ; Wed, 28 Sep 2022 10:44:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1664387069; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=1jdTlaHlqUGsp+WQYmTbrToN1KOLkOWoz/mZqD7wNkI=; b=SFYZdnBINAJBQ9kAKFfv1bs6+xL+bbnL5wJiCprWoxwrpVPsU3Y6XyrrL8gsmt4qMlvN9b /w/QNujCwLLfl1Y45bQb8zs47p2g9eErIrteAedP+fVYseX9zqZeQjQguKx9x9mcsgC3i4 JU/X9I0IPgyTLDYCozkngBgPUPDgpHc= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-515-jTqblEF3M-ypPsQpFngd5Q-1; Wed, 28 Sep 2022 13:44:26 -0400 X-MC-Unique: jTqblEF3M-ypPsQpFngd5Q-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 6831B101AA5B; Wed, 28 Sep 2022 17:44:25 +0000 (UTC) Received: from starship (unknown [10.40.193.233]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2B6791121314; Wed, 28 Sep 2022 17:44:23 +0000 (UTC) Message-ID: Subject: Re: [PATCH] KVM: x86: disable on 32-bit unless CONFIG_BROKEN From: Maxim Levitsky To: Sean Christopherson , Paolo Bonzini Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Date: Wed, 28 Sep 2022 20:44:22 +0300 In-Reply-To: References: <20220926165112.603078-1-pbonzini@redhat.com> <15291c3f-d55c-a206-9261-253a1a33dce1@redhat.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.5 (3.36.5-2.fc32) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2022-09-28 at 16:12 +0000, Sean Christopherson wrote: > On Wed, Sep 28, 2022, Paolo Bonzini wrote: > > On 9/28/22 09:10, Maxim Levitsky wrote: > > > I also think that outside KVM developers nobody should be using KVM on 32 bit host. > > > > > > However for_developement_ I think that 32 bit KVM support is very useful, as it > > > allows to smoke test the support for 32 bit nested hypervisors, which I do once in a while, > > > and can even probably be useful to some users (e.g running some legacy stuff in a VM, > > > which includes a hypervisor, especially to run really legacy OSes / custom bare metal software, > > > using an old hypervisor) - or in other words, 32 bit nested KVM is mostly useless, but > > > other 32 bit nested hypervisors can be useful. > > > > > > Yes, I can always use an older 32 bit kernel in a guest with KVM support, but as long > > > as current kernel works, it is useful to use the same kernel on host and guest. > > > > Yeah, I would use older 32 bit kernels just like I use RHEL4 to test PIT > > reinjection. :) But really the ultimate solution to this would be to > > improve kvm-unit-tests so that we can compile vmx.c and svm.c for 32-bit. > > Agreed. I too use 32-bit KVM to validate KVM's handling of 32-bit L1 hypervisors, > but the maintenance cost is painfully high. > But is it actually? I test it routinely and it it does work quite well IMHO. I don't remember that there were that much breakage lately in this area. As far as my opinion goes I do volunteer to test this code more often, and I do not want to see the 32 bit KVM support be removed *yet*. Best regards, Maxim Levitsky