Status of 64 bit DomU PVs?

[Roger Pau Monné]

On 05/04/14 15:14, Cherry G. Mathew wrote:
> Hi Jonni,
> 
> Date: Sat, 05 Apr 2014 00:39:24 +0300
>> From: Jonni Nakari <jonni at egarden.fi>
>> To: freebsd-xen at freebsd.org
>> Subject: Status of 64 bit DomU PVs?
>> Message-ID: <533F268C.8040909 at egarden.fi>
>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>
>> Hello,
>> what is the current status of 64 bit paravirtualized FreeBSD? The wiki
>> page Xen wiki page [1] states that only i386 kernels can be run in fully
>> paravirtualized mode. The wiki page hasn't been updated in a while. Has
>> anything changed since the last update?
>>
>> I would like to run FreeBSD as a DomU on a AMD 64 bit machine that does
>> not have hardware accelerated virtualization. That propably means that
>> it's not feasible to run a HVM based DomU on the machine? I would also
>> like the DomU to be 64 bit to provide more than 4 gigabytes of RAM to
>> the ZFS serving FreeBSD.
>>
>>
> I've been working on this for quite some time now (perhaps too long), and
> the bad news is that, no, it's not ready for use - the code on the branch
> does bring us up to single user mode, but I'm reworking the pmap module
> with the wisdom of hindsight. The good news is that it should be ready for
> testing "soon" (May, 2014).
> 
> With PV on 64bit, you should be able to have a 64bit address space with
> support for 47bit RAM (in theory).
> 
> 
> 
>> Or maybe I have misunderstood something. Is it possible to provide more
>> than 4 GB RAM for a 32 bit DomU so that it can use all of it for ZFS
>> caching?
>>
>>
> On 64bit PV, the DomU is 64bit (although there used to be support for 32bit
> PV on 64bit hypervisor until the 3.x hypervisors, iirc). So yes, you should
> in *theory*, be able to have more than 4GB ram for your 64bit DomU.

Just to clarify, a 64-bit Xen Hypervisor is perfectly capable of running
32-bit PV guests, support for 32-bit guests has never been removed from
the hypervisor.

Roger.