Avi Kivity wrote:

Sander van Leeuwen wrote:

You are mistaken. VT-x allows multiple clients to work concurrently.
There's only one catch: all those
clients should follow certain guidelines.


Currently, kvm assumes that it is the only user that issues vmptrld
instructions.  There may me other such assumptions in the code.

There is also the question of who issues the vmxon/vmxoff instructions
and set the magic msr bits that enable kvm.  You can't have two
hypervisors doing that; that would be racy.  It should be possible to
abstract those bits out to something outside kvm, but I don't see that
happening.

VirtualBox currently always executes vmxon when it wants to execute some guest code. When leaving
ring 0 it issues the corresponding vmxoff. While that may increase world switch overhead, it has not turned
out to be an issue for us. I think it's a bit risky to use somebody else's vmxon pointer.

You have a point with the msr updates though.

-- 
Kind regards / mit freundlichen Gruessen / Met vriendelijke groet
  Sander van Leeuwen

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