Re: rendezvousing all physical CPUs

[Keir Fraser <keir@xensource.com>]

On 1/12/06 08:16, "Jan Beulich" <jbeulich@novell.com> wrote:

>> How about providing the linear address of a chunk of dom0 code that Xen
>> should run in ring 0 with CPUs in a particular configuration? We could
>> provide flags to represent useful configurations: e.g., run on all CPUs
>> atomicaly, run on CPU0 only and quiesce others, etc.
> 
> Hmm??? I would have to question why dom0 currently gets run in ring 1 then.

Uniformity with execution of other domains and it's also a useful safety
mechanism for catching dom0 bugs. It is *not* for security reasons!

> I would at best consider allowing the guest to pass a batch of operations that
> it wants carried out - I/O memory accesses (normal RAM not allowed), MSR
> reads/writes, port I/O. However, for the specific case of the RNG, PCI config
> space accesses would also need to be supported - while they can be reduced
> to iomem or port accesses, abstracting this out from the requester and from
> Xen would require some thought.

Dom0 can map any memory, DMA to any memory, and with your original proposed
hypercall would be able to tear down physical CPUs for unbounded time
periods. It 0wns the machine already. ;-)

 -- Keir