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 X-Spam-Level: X-Spam-Status: No, score=-6.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 67A7FC47082 for ; Wed, 26 May 2021 11:10:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 44D986128D for ; Wed, 26 May 2021 11:10:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234172AbhEZLL6 (ORCPT ); Wed, 26 May 2021 07:11:58 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:39541 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234006AbhEZLLz (ORCPT ); Wed, 26 May 2021 07:11:55 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1622027422; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=FvJbAVf0Tb1ulZyuUSwZ0lrOmeUKOAeH734xKBdluCA=; b=TWYNmpTtMYQH5LfN3Q//aBclg/kHIlaV84y5lQc54Ni4DEx07JCBVa5kFVunCnzMcCWQRE BOov1ikWWyhi5UJB7OVJ2DIcOETirNTf1qOACP4TK9c1s3KMWPHguqppNZ7r8/73dOJzHS KxT/m12iKlIEJ7oxt5P3O8TU3MeyGdk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-515-dx5q9S1fO7OcQHJE81YmsA-1; Wed, 26 May 2021 07:10:21 -0400 X-MC-Unique: dx5q9S1fO7OcQHJE81YmsA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D87AF6D5C2; Wed, 26 May 2021 11:10:19 +0000 (UTC) Received: from starship (unknown [10.40.192.15]) by smtp.corp.redhat.com (Postfix) with ESMTP id D9A8378623; Wed, 26 May 2021 11:10:11 +0000 (UTC) Message-ID: <2fd417c59f40bd10a3446f9ed4be434e17e9a64f.camel@redhat.com> Subject: Re: Writable module parameters in KVM From: Maxim Levitsky To: Paolo Bonzini , Ben Gardon , Sean Christopherson , Jim Mattson , Junaid Shahid , Peter Xu , LKML , kvm Date: Wed, 26 May 2021 14:10:10 +0300 In-Reply-To: <35fe7a86-d808-00e9-a6aa-e77b731bd4bf@redhat.com> References: <35fe7a86-d808-00e9-a6aa-e77b731bd4bf@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 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2021-05-26 at 12:49 +0200, Paolo Bonzini wrote: > On 26/05/21 01:45, Ben Gardon wrote: > > At Google we have an informal practice of adding sysctls to control some > > KVM features. Usually these just act as simple "chicken bits" which > > allow us to turn off a feature without having to stall a kernel rollout > > if some feature causes problems. (Sysctls were used for reasons specific > > to Google infrastructure, not because they're necessarily better.) > > > > We'd like to get rid of this divergence with upstream by converting the > > sysctls to writable module parameters, but I'm not sure what the general > > guidance is on writable module parameters. Looking through KVM, it seems > > like we have several writable parameters, but they're mostly read-only. > > Sure, making them writable is okay. Most KVM parameters are read-only > because it's much simpler (the usecase for introducing them was simply > "test what would happen on old processors"). What are these features > that you'd like to control? > > > I also don't see central documentation of the module parameters. They're > > mentioned in the documentation for other features, but don't have their > > own section / file. Should they? > > They probably should, yes. > > Paolo > I vote (because I have fun with my win98 once in a while), to make 'npt' writable, since that is the only way to make it run on KVM on AMD. My personal itch only though! Best regards, Maxim Levitsky