Re: [Qemu-devel] Will the ELI incorporated in theKVM?

[Avi Kivity <avi@redhat.com>]

On 09/19/2012 05:10 PM, Jan Kiszka wrote:
>> Although ELI works today, I'd be happy to
>> hear what parts of it you find "invasive" and "imperfect" (what
>> software ever is perfect?)
> 
> It's imperfect as you need to dedicate a core to pure guest-mode load
> and cannot run userspace on that core (cannot walk through
> userspace-based device models e.g.). And it requires that magic bar to
> map the shadow IDT into the guest (hmm, I think Hitachi avoided this).
> 
> It's invasive as it has to change Linux to maintain those isolated slave
> CPUs. That is, of course, based on code that was published by Hitachi.
> Yours may differ but will still have to solve the same problems.
> 
> Back then in our discussion, it was unclear if and when real hardware
> will actually show up. Now the spec is already there, hardware should
> follow within months (typically). I'm not aware of limitations regarding
> zero-exit virtualization so far. But please share any insights you
> collected from studying the specs or recent patches!

This matches my thoughts on the matter exactly.  I would add that ELI
adds a maintenance burden of supporting rarely used code, as ELI can
hardly be called mainstream.  On the other hand, the new hardware
support will be used by every guest running on new hardware, for IPIs,
virtual interrupts, and assigned device interrupts.

-- 
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