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 2C087C169C4 for ; Mon, 11 Feb 2019 17:34:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F285121B18 for ; Mon, 11 Feb 2019 17:34:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731706AbfBKRe0 (ORCPT ); Mon, 11 Feb 2019 12:34:26 -0500 Received: from mga01.intel.com ([192.55.52.88]:49856 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727393AbfBKRe0 (ORCPT ); Mon, 11 Feb 2019 12:34:26 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 11 Feb 2019 09:34:25 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.58,359,1544515200"; d="scan'208";a="117035838" Received: from ahduyck-desk1.jf.intel.com ([10.7.198.76]) by orsmga008.jf.intel.com with ESMTP; 11 Feb 2019 09:34:25 -0800 Message-ID: <96285ed154dbb92686ca0068e21f5e0500bb1ce7.camel@linux.intel.com> Subject: Re: [RFC PATCH 2/4] kvm: Add host side support for free memory hints From: Alexander Duyck To: "Michael S. Tsirkin" , Alexander Duyck Cc: 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 Date: Mon, 11 Feb 2019 09:34:25 -0800 In-Reply-To: <20190209194108-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> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5 (3.28.5-2.fc28) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.