Re: New VT-D spec available

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Nakajima, Jun wrote:
> An updated specification (Rev 1.0 update) of Intel(r) virtualization
> technology for Directed I/O is now available on Intel web site: 
>
> http://download.intel.com/technology/computing/vptech/Intel(r)_VT_for_Di
> rect_IO.pdf 
>
> The specification update includes DMA remapping capability, Interrupt
> remapping capability, queue management, invalidation information and
> enhancements.
>
> We are thinking how this should be enabled for KVM as well especially
> when assigning real devices to guests. Suggestions are welcome.
>   

I've had a quick look-see. There are two general approaches which I 
think make sense:

- tightly coupled kvm integration, where kvm is extended with a 
root-only 'assign pci dev x to this vm'.  As the page table format is 
the same as used by ept (I'm guessing... haven't actually read the ept 
spec), this should be quite easy to do on once npt/ept support is 
integrated.

- general interface for manipulating VT-d, with the ability to use it 
with kvm.  With this, it is possible to assign pci devices to ordinary 
userspace processes, some of which could be hosting virtual machines.  
This may fit will with the UIO patchset.

Unless I misread things, VT-d does not honor the U/S bit on the page 
table entries.  That makes the general approach fairly difficult.  I 
would recommend starting with the tightly-coupled, less generic approach 
first, and generalizing it if/when there is demand for it.

-- 
error compiling committee.c: too many arguments to function


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