Messages in this thread | | | Date | Wed, 2 Jun 2010 14:19:28 +0200 | From | Joerg Roedel <> | Subject | Re: [PATCH] VFIO driver: Non-privileged user level PCI drivers |
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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
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