Virtual machines

[James P White]

At 12:26 PM 5/22/97 -0400, Terrence W. Zellers wrote:
>
>On Thu, 22 May 1997, Dwight Hughes wrote:
>
>> | From: Terrence W. Zellers <zellert@voicenet.com>
>> |  
>> |    IMO it ***MUST*** be capable of fully virtualizing itself in 
>> | execution, not just emulation.   This means it must have a paging
>> | prefix algorithm, the ability to intercept any instructions which
>
>> Can this be done with an i486 or Pentium? Does it require special
>> hardware to pull it off properly?
>
>    The x86 architecture is NOT self virtualizable, no, but we're
>discussing an idealized VM to be emulated.  That can be done, of
>course, though at greater overhead than true on virtualizable hardware.
>A fair amount of the FREEVM discussion touched on that.

The x86 VM (386 and up) *is* self virtualizable using exactly the same
techniques as the IBM VM architecture (memory and i/o
mapping/paging/trapping, exception trapping and emulation, privilege
limits/exceptions).

It is interesting to note that, AFAIK, no commercial OS for the x86 bothers
to support self virtual operation.  They all use it for security sandboxes.

Jim
-----------------------------------------------------------------------
James P. White                        Netscape DevEdge Champion for IFC
Director of Technology Adventure Online Gaming http://www.gameworld.com
Developers of Gameworld -- Live Action Role-Playing and Strategic Games
jim@pagesmiths.com        Pagesmiths' home is http://www.pagesmiths.com