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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 BD8F8C282D7 for ; Mon, 11 Feb 2019 17:37:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 989D0222A0 for ; Mon, 11 Feb 2019 17:37:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731920AbfBKRg7 (ORCPT ); Mon, 11 Feb 2019 12:36:59 -0500 Received: from mx1.redhat.com ([209.132.183.28]:39634 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726243AbfBKRg6 (ORCPT ); Mon, 11 Feb 2019 12:36:58 -0500 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 2159DB650; Mon, 11 Feb 2019 17:36:58 +0000 (UTC) Received: from redhat.com (ovpn-120-40.rdu2.redhat.com [10.10.120.40]) by smtp.corp.redhat.com (Postfix) with SMTP id 163AE1850E; Mon, 11 Feb 2019 17:36:55 +0000 (UTC) Date: Mon, 11 Feb 2019 12:36:55 -0500 From: "Michael S. Tsirkin" To: Alexander Duyck Cc: Alexander Duyck , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, rkrcmar@redhat.com, x86@kernel.org, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, pbonzini@redhat.com, tglx@linutronix.de, akpm@linux-foundation.org Subject: Re: [RFC PATCH 2/4] kvm: Add host side support for free memory hints Message-ID: <20190211123638-mutt-send-email-mst@kernel.org> References: <20190204181118.12095.38300.stgit@localhost.localdomain> <20190204181546.12095.81356.stgit@localhost.localdomain> <20190209194108-mutt-send-email-mst@kernel.org> <96285ed154dbb92686ca0068e21f5e0500bb1ce7.camel@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <96285ed154dbb92686ca0068e21f5e0500bb1ce7.camel@linux.intel.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Mon, 11 Feb 2019 17:36:58 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 11, 2019 at 09:34:25AM -0800, Alexander Duyck wrote: > On Sat, 2019-02-09 at 19:44 -0500, Michael S. Tsirkin wrote: > > On Mon, Feb 04, 2019 at 10:15:46AM -0800, Alexander Duyck wrote: > > > From: Alexander Duyck > > > > > > Add the host side of the KVM memory hinting support. With this we expose a > > > feature bit indicating that the host will pass the messages along to the > > > new madvise function. > > > > > > This functionality is mutually exclusive with device assignment. If a > > > device is assigned we will disable the functionality as it could lead to a > > > potential memory corruption if a device writes to a page after KVM has > > > flagged it as not being used. > > > > I really dislike this kind of tie-in. > > > > Yes right now assignment is not smart enough but generally > > you can protect the unused page in the IOMMU and that's it, > > it's safe. > > > > So the policy should not leak into host/guest interface. > > Instead it is better to just keep the pages pinned and > > ignore the hint for now. > > Okay, I can do that. It also gives me a means of benchmarking just the > hypercall cost versus the extra page faults and zeroing. Good point. Same goes for poisoning :)