On Wed, Jun 02, 2010 at 01:12:25PM +0200, Joerg Roedel wrote: > On Wed, Jun 02, 2010 at 01:38:28PM +0300, Michael S. Tsirkin wrote: > > On Wed, Jun 02, 2010 at 12:35:16PM +0200, Joerg Roedel wrote: > > > > With the userspace interface a process can create io-page-faults > > > anyway if it wants. We can't protect us from this. > > > > We could fail all operations until an iommu is bound. This will help > > catch bugs with access before setup. We can not do this if a domain is > > bound by default. > > 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. > > > The second IOMMU_MAP ioctl is just to show that existing mappings would > > > be destroyed if the device is assigned to another address space. Not > > > strictly necessary. So we have two ioctls but save one call to create > > > the iommu-domain. > > > > 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. > 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. > I think my proposal does not have any > extra costs. with my proposal we have 1 ioctl per device + 1 per domain. with yours we have 2 ioctls per device is iommu is shared and 1 if it is not shared. as current apps share iommu it seems to make sense to optimize for that. > > > Because we express here that "dev2 shares the iommu mappings of dev1". > > > Thats easy to remember. > > > > they both share the mappings. which one gets the iommu > > destroyed (breaking the device if it is now doing DMA)? > > 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. -- 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
