From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH v3 0/3] virtio DMA API core stuff Date: Fri, 20 Nov 2015 08:56:46 +0200 Message-ID: <20151120083857-mutt-send-email-mst@redhat.com> References: <20151119153821-mutt-send-email-mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Andy Lutomirski Cc: linux-s390 , KVM , Benjamin Herrenschmidt , Sebastian Ott , "linux-kernel@vger.kernel.org" , Linux Virtualization , Christian Borntraeger , Joerg Roedel , Martin Schwidefsky , Paolo Bonzini , David Woodhouse , Christoph Hellwig List-Id: virtualization@lists.linuxfoundation.org On Thu, Nov 19, 2015 at 01:59:05PM -0800, Andy Lutomirski wrote: > On Nov 19, 2015 5:45 AM, "Michael S. Tsirkin" wrote: > > > > On Tue, Oct 27, 2015 at 11:38:57PM -0700, Andy Lutomirski wrote: > > > This switches virtio to use the DMA API unconditionally. I'm sure > > > it breaks things, but it seems to work on x86 using virtio-pci, with > > > and without Xen, and using both the modern 1.0 variant and the > > > legacy variant. > > > > So thinking hard about it, I don't see any real drawbacks to making this > > conditional on a new feature bit, that Xen can then set.. > > Can you elaborate? If I run QEMU, hosting Xen, hosting Linux, and the > virtio device is provided by QEMU, then how does Xen set the bit? You would run QEMU with the appropriate flag. E.g. -global virtio-pci,use_platform_dma=on > Similarly, how would Xen set the bit for a real physical device? > > > --Andy There's no need to set bits for physical devices I think: from security point of view, using them from a VM isn't very different from using them from host. -- MST