On Wednesday 02 June 2010 10:46:15 am Chris Wright wrote: > * Joerg Roedel (joro@xxxxxxxxxx) wrote: > > On Wed, Jun 02, 2010 at 02:21:00PM +0300, Michael S. Tsirkin wrote: > > > On Wed, Jun 02, 2010 at 01:12:25PM +0200, Joerg Roedel wrote: > > > > > > Even if it is bound to a domain the userspace driver could program the > > > > device to do dma to unmapped regions causing io-page-faults. The kernel > > > > can't do anything about it. > > > > > > It can always corrupt its own memory directly as well :) > > > But that is not a reason not to detect errors if we can, > > > and not to make APIs hard to misuse. > > > > Changing the domain of a device while dma can happen is the same type of > > bug as unmapping potential dma target addresses. We can't catch this > > kind of misuse. > > > > > > > With 10 devices you have 10 extra ioctls. > > > > > > > > And this works implicitly with your proposal? > > > > > > Yes. so you do: > > > iommu = open > > > ioctl(dev1, BIND, iommu) > > > ioctl(dev2, BIND, iommu) > > > ioctl(dev3, BIND, iommu) > > > ioctl(dev4, BIND, iommu) > > > > > > No need to add a SHARE ioctl. > > > > In my proposal this looks like: > > > > > > dev1 = open(); > > ioctl(dev2, SHARE, dev1); > > ioctl(dev3, SHARE, dev1); > > ioctl(dev4, SHARE, dev1); > > > > So we actually save an ioctl. > > This is not any hot path, so saving an ioctl shouldn't be a consideration. > Only important consideration is a good API. I may have lost context here, > but the SHARE API is limited to the vfio fd. The BIND API expects a new > iommu object. Are there other uses for this object? Tom's current vfio > driver exposes a dma mapping interface, would the iommu object expose > one as well? Current interface is device specific DMA interface for > host device drivers typically mapping in-flight dma buffers, and IOMMU > specific interface for assigned devices typically mapping entire virtual > address space. Actually, it a domain object - which may be usable among iommus (Joerg?). However, you can't really do the dma mapping with just the domain because every device supports a different size address space as a master, i.e., the dma_mask. And I don't know how kvm would deal with devices with varying dma mask support, or why they'd be in the same domain. -- 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
