[RFC] Hypervisor, x86 emulation deprivileged

[Anthony PERARD <anthony.perard@citrix.com>]

Hi,

I've taken over the work from Ben to have a deprivileged mode in the
hypervisor, but I'm unsure about which direction to take.

First, after understanding what have been done, and fixing a few things,
I did some benchmark to compare a simple "device" running in ring0 to
the same one running in ring3 and also in QEMU. This "device" would call
'rdtsc' on 'outl' and return the value in 'inl' (I actually do not use
the value). The measurement is done from a kernel module in the guest
(simply rdtsc;inl;rdtsc multiple time). This is the result I've found:

    ring3 ~3.5x slower than ring0
    qemu   ~22x slower than ring0
          ~6.5x slower than ring3

So that would be the worst-case scenario, where an emulator barely do
anything.


There have been different methods proposed to do the depriv mode, in
<55A8D477.2060909@citrix.com>, one of which was to implement a per-vcpu
stack which could be more elegant.

So, would you suggest that I start working on a per-vcpu stack? Or
should I continue with the current direction?


Some of the code I have, including the code for the benchmark, can be
found here:
git://xenbits.xen.org/people/aperard/xen-unstable.git
branch: hvm-x86-deprivileged-mode-wip

Regards,

-- 
Anthony PERARD

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