svn commit: r255744 - in head/sys: amd64/amd64 amd64/conf amd64/include i386/conf i386/i386 i386/include kern x86/xen xen

Justin T. Gibbs gibbs at freebsd.org
Fri Sep 27 22:34:47 UTC 2013


On Sep 27, 2013, at 11:33 PM, Benjamin Kaduk <bjkfbsd at gmail.com> wrote:

> On Fri, Sep 20, 2013 at 6:59 PM, Justin T. Gibbs <gibbs at freebsd.org> wrote:
> Author: gibbs
> Date: Fri Sep 20 22:59:22 2013
> New Revision: 255744
> URL: http://svnweb.freebsd.org/changeset/base/255744
> 
> Log:
>   Merge Xen PVHVM support into the GENERIC kernel config for both
>   amd64 and i386.
> 
> I confess to a poor understanding of the reason for existence of sys/i386/conf/XEN -- in particular, does this change render that configuration obsolete as well as XENHVM?  Maybe -hackers would be a better place to ask...
> 
> Thanks,
> 
> Ben 

sys/i386/conf/XEN is for a fully para-virtualized FreeBSD configuration.  This means that nothing is emulated and all aspects of the kernel (VM, device drivers, etc) are using hypervisor services to do their job.  FreeBSD's full PV implementation is not production ready.  However, full PV is currently required for DOM0 support and work is currently underway to improve it for at least amd64.

HVM with PV optimizations is another guest mode for Xen.  Recent changes make it possible for FreeBSD to cleanly detect it is running on Xen and enable these optimizations without having to build a custom kernel.  For this reason, the XENHVM config was removed.

--
Justin


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