From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:7884 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727644AbgBXS7k (ORCPT ); Mon, 24 Feb 2020 13:59:40 -0500 Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 01OInlFi069974 for ; Mon, 24 Feb 2020 13:59:39 -0500 Received: from e06smtp02.uk.ibm.com (e06smtp02.uk.ibm.com [195.75.94.98]) by mx0b-001b2d01.pphosted.com with ESMTP id 2yaxt7gkeu-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Mon, 24 Feb 2020 13:59:38 -0500 Received: from localhost by e06smtp02.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 24 Feb 2020 18:59:37 -0000 Date: Mon, 24 Feb 2020 19:59:28 +0100 From: Halil Pasic Subject: Re: [PATCH 2/2] virtio: let virtio use DMA API when guest RAM is protected In-Reply-To: <20200221163645.GB10054@lst.de> References: <20200220160606.53156-1-pasic@linux.ibm.com> <20200220160606.53156-3-pasic@linux.ibm.com> <20200220161309.GB12709@lst.de> <20200221025915.GB2298@umbus.fritz.box> <20200221163645.GB10054@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8bit Message-Id: <20200224195928.654694fd.pasic@linux.ibm.com> Sender: linux-s390-owner@vger.kernel.org List-ID: To: Christoph Hellwig Cc: David Gibson , "Michael S. Tsirkin" , Jason Wang , Marek Szyprowski , Robin Murphy , linux-s390@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, Christian Borntraeger , Janosch Frank , Viktor Mihajlovski , Cornelia Huck , Ram Pai , Thiago Jung Bauermann , "Lendacky, Thomas" , Michael Mueller On Fri, 21 Feb 2020 17:36:45 +0100 Christoph Hellwig wrote: > > By "legacy devices" I assume you mean pre-virtio-1.0 devices, that > > lack the F_VERSION_1 feature flag. Is that right? Because I don't > > see how being a legacy device or not relates to use of the DMA API. > > No. "legacy" is anything that does not set F_ACCESS_PLATFORM. FYI in virtio-speak the term 'legacy devices' is already taken and it ain't congruent with your intended semantics. Please look it up https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/virtio-v1.1-cs01.html#x1-60001 But with that understood your statement does provide insisting in how do you see F_ACCESS_PLATFORM. I.e. something that should be enabled in general, except for legacy reasons. But I'm afraid Michael sees it differently: i.e. something that should be enabled when necessary, and otherwise not (because it is likely to cost performance). Regards, Halil