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[Xen-users] Re: Merge Xen (the hypervisor) into Linux

On Tue, 2 Jun 2009, Joel Becker wrote:

[ Speaking as me, no regard to $EMPLOYER ]

On Wed, Jun 03, 2009 at 01:28:43AM +0200, Ingo Molnar wrote:
A lot of Xen legacies could be dropped: the crazy ring1 hack on
32-bit, the various wide interfaces to make pure-software
virtualization limp along. All major CPUs shipped with hardware
virtualization support in the past 2-3 years, so the availability of
VMX and SVM can be taken for granted for such a project.

        The biggest reason I personally want Xen to be in mainline is
PVM.  Dropping PVM is, to me, pretty much saying "let's merge Xen
without taking the useful parts."

        So I want to see PVM continue for a long time.  I'd like it to
be something I can get with mainline Linux.  I don't care if it is dom0,
dom0 and the hypervisor, whatever.  I just don't want to have to be
patching out-of-tree patches for a pretty basic functionality.
        I don't see 2-3 years as a time frame to assume "everyone has
one."  Otherwise, why does Linux have code for x86_32?  Everyone's had a
64bit system for at least that long.  Sure, that's a straw man.  It goes
both ways.

it's always easier to continue to support stuff that you already have in place than it is to add new things.

if the non PVM stuff could be added to the kernel, how much would that simplify the code needed to support PVM? would that reduce the amount of effort that the Xen people need to spend to something that would mean that they would be able to keep up with fairly recent kernels?

or what about getting the non PVM version in, and then making the seperate argument to add PVM support with a different config option ('xen support for older CPU's, note there is a performance degredation if this option is selected'), distros could support Xen in their main kernel package on new hardware, and users like you could enable the slower version.

David Lang

note: I am not an approver in this process, just an interested observer (who doesn't use Xen)

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