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See http://www.infradead.org/rpr.html Cc: jgross@suse.com, Peng Fan , x86@kernel.org, konrad.wilk@oracle.com, jasowang@redhat.com, "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, iommu@lists.linux-foundation.org, linux-imx@nxp.com, xen-devel@lists.xenproject.org, boris.ostrovsky@oracle.com, linux-arm-kernel@lists.infradead.org X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Mon, Jun 29, 2020 at 04:46:09PM -0700, Stefano Stabellini wrote: > > I could imagine some future Xen hosts setting a flag somewhere in the > > platform capability saying "no xen specific flag, rely on > > "VIRTIO_F_ACCESS_PLATFORM". Then you set that accordingly in QEMU. > > How about that? > > Yes, that would be fine and there is no problem implementing something > like that when we get virtio support in Xen. Today there are still no > virtio interfaces provided by Xen to ARM guests (no virtio-block/net, > etc.) > > In fact, in both cases we are discussing virtio is *not* provided by > Xen; it is a firmware interface to something entirely different: > > 1) virtio is used to talk to a remote AMP processor (RPMesg) > 2) virtio is used to talk to a secure-world firmware/OS (Trusty) > > VIRTIO_F_ACCESS_PLATFORM is not set by Xen in these cases but by RPMesg > and by Trusty respectively. I don't know if Trusty should or should not > set VIRTIO_F_ACCESS_PLATFORM, but I think Linux should still work > without issues. > Any virtio implementation that is not in control of the memory map (aka not the hypervisor) absolutely must set VIRTIO_F_ACCESS_PLATFORM, else it is completely broken. > The xen_domain() check in Linux makes it so that vring_use_dma_api > returns the opposite value on native Linux compared to Linux as Xen/ARM > DomU by "accident". By "accident" because there is no architectural > reason why Linux Xen/ARM DomU should behave differently compared to > native Linux in this regard. > > I hope that now it is clearer why I think the if (xen_domain()) check > needs to be improved anyway, even if we fix generic dma_ops with virtio > interfaces missing VIRTIO_F_ACCESS_PLATFORM. IMHO that Xen quirk should never have been added in this form.. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu