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. > > Remember that we still need to be able to provide seperate mappings > > for each device to support IOMMU emulation for the guest. > > Generally not true. E.g. guest can enable iommu passthrough > or have domain per a group of devices. What I meant was that there may me multiple io-addresses spaces necessary for one process. I didn't want to say that every device _needs_ to have its own address space. > > As I wrote the domain has a reference count and is destroyed only when > > it goes down to zero. This does not happen as long as a device is bound > > to it. > > > > Joerg > > We were talking about UNSHARE ioctl: > ioctl(dev1, UNSHARE, dev2) > Does it change the domain for dev1 or dev2? > If you make a mistake you get a hard to debug bug. As I already wrote we would have an UNBIND ioctl which just removes a device from its current domain. UNBIND is better than UNSHARE for exactly the reason you pointed out above. I thought I stated that already. Joerg -- 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
