From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755183AbbJ1CHI (ORCPT ); Tue, 27 Oct 2015 22:07:08 -0400 Received: from mx2.suse.de ([195.135.220.15]:51521 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754077AbbJ1CHF (ORCPT ); Tue, 27 Oct 2015 22:07:05 -0400 Date: Wed, 28 Oct 2015 11:06:50 +0900 From: Joerg Roedel To: Andy Lutomirski Cc: linux-kernel@vger.kernel.org, Christian Borntraeger , Cornelia Huck , Sebastian Ott , Paolo Bonzini , Christoph Hellwig , benh@kernel.crashing.org, KVM , dwmw2@infradead.org, Martin Schwidefsky , linux-s390 , Andy Lutomirski Subject: Re: [PATCH 2/3] virtio_ring: Support DMA APIs Message-ID: <20151028020650.GA18467@suse.de> References: <6b42014d04258c706c7c43ae739efb30e32496b9.1445994839.git.luto@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6b42014d04258c706c7c43ae739efb30e32496b9.1445994839.git.luto@kernel.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Andy, On Tue, Oct 27, 2015 at 06:17:09PM -0700, Andy Lutomirski wrote: > From: Andy Lutomirski > > virtio_ring currently sends the device (usually a hypervisor) > physical addresses of its I/O buffers. This is okay when DMA > addresses and physical addresses are the same thing, but this isn't > always the case. For example, this never works on Xen guests, and > it is likely to fail if a physical "virtio" device ever ends up > behind an IOMMU or swiotlb. The overall code looks good, but I havn't seen and dma_sync* calls. When swiotlb=force is in use this would break. > + vq->vring.desc[head].addr = cpu_to_virtio64(_vq->vdev, vring_map_single( > + vq, > + desc, total_sg * sizeof(struct vring_desc), > + DMA_TO_DEVICE)); Nit: I think readability could be improved here by using a temporary variable for the return value of vring_map_single(). Joerg