On Wed, Apr 27, 2016 at 04:23:32PM +0200, 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. QEMU can choose to bypass IOMMU for one device and not the other. IOMMU in QEMU isn't involved when it's bypassed. > So any fix here belongs > into the platform/iommu code too and not into some driver. Fine but this is beside the point. Almost all virtio devices bypass IOMMU and what this patch does is create a way to detect devices that don't. This code can maybe go into platform. > > 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. > > > > Joerg It would be easy if they did but they don't do this on all systems. In particular the idea for firmware interface was clearly that a given bus either is connected through IOMMU or bypassing it. Whether virtio bypasses the iommu is unrelated to the bus it's on. -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
