From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api Date: Wed, 27 Apr 2016 17:38:51 +0300 Message-ID: <20160427173603-mutt-send-email-mst@redhat.com> References: <1461245745-6710-1-git-send-email-mst@redhat.com> <20160421135416.GE11775@citrix.com> <1461759501.118304.149.camel@infradead.org> <20160427153345-mutt-send-email-mst@redhat.com> <20160427142331.GH17926@8bytes.org> 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: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Andy Lutomirski Cc: Kevin Wolf , Anthony PERARD , Cornelia Huck , Wei Liu , Stefan Hajnoczi , qemu-block-qX2TKyscuCcdnm+yROfE0A@public.gmane.org, Stefano Stabellini , "qemu-devel-qX2TKyscuCcdnm+yROfE0A@public.gmane.org Developers" , peterx-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Christian Borntraeger , iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, Andy Lutomirski , kvm list , Amit Shah , Paolo Bonzini , Linux Virtualization , David Woodhouse , Jason Wang List-Id: iommu@lists.linux-foundation.org On Wed, Apr 27, 2016 at 07:31:43AM -0700, Andy Lutomirski wrote: > On Wed, Apr 27, 2016 at 7:23 AM, Joerg Roedel wrote: > > On Wed, Apr 27, 2016 at 04:37:04PM +0300, Michael S. Tsirkin wrote: > >> One correction: it's a feature of the device in the system. > >> There could be a mix of devices bypassing and not > >> bypassing the IOMMU. > > > > No, it really is not. A device can't chose to bypass the IOMMU. But the > > IOMMU can chose to let the device bypass. So any fix here belongs > > into the platform/iommu code too and not into some driver. > > > >> Sounds good. And a way to detect appropriate devices could > >> be by looking at the feature flag, perhaps? > > > > Again, no! The way to detect that is to look into the iommu description > > structures provided by the firmware. They provide everything necessary > > to tell the iommu code which devices are not translated. > > > > Except on PPC and SPARC. As far as I know, those are the only > problematic platforms. > > Is it too late to *disable* QEMU's q35-iommu thingy until it can be > fixed to report correct data in the DMAR tables? > > --Andy Meaning virtio or assigned devices? For virtio - it's way too late since these are working configurations. For assigned devices - they don't work on x86 so it doesn't have to be disabled, it's safe to ignore. -- MST