Xen, PAE, and NetBSD

On Sun, Feb 11, 2007 at 12:25:10AM -0500, Todd Vierling
wrote:
> Runs fine on a PAE mode 32-bit Linux host that you do
not have the
> option to reconfigure?

Out of technical curiosity:
Why does a domU have to support PAE? AFAIK the page table is
managed by
the Hypervisor. Is the interface to the Hypervisor so badly
designed
that it can't hide such details?

	Kind regards

-- 
Matthias Scheler                                  http://zhadum.org.uk/

On 2/12/07, Matthias Scheler <tronzhadum.org.uk> wrote:
> > Runs fine on a PAE mode 32-bit Linux host that you
do not have the
> > option to reconfigure?
>
> Out of technical curiosity:
> Why does a domU have to support PAE? AFAIK the page
table is managed by
> the Hypervisor. Is the interface to the Hypervisor so
badly designed
> that it can't hide such details?

See messages in mail-index:port-xen for August 2006, with
the subject

    Xen3/PAE problems with domainU

There are some web link pointers to xen-users in that
thread.  What I
gathered from it without digging for major technical details
is that
the page tables are manipulated in a native-like format in
all
domains, so their structural layout must match in all
domains (PAE vs.
non-PAE).

>From a user's perspective, if you try to load a
non-PAE-capable domU
on a PAE host, xend will spit out EINVAL and refuse to
complete the
domain construction.

-- 
-- Todd Vierling <tvduh.org> <tvpobox.com> <toddvierling.name>

On 2/12/07, Matthias Scheler <tronzhadum.org.uk> wrote:
> > Runs fine on a PAE mode 32-bit Linux host that you
do not have the
> > option to reconfigure?
>
> Out of technical curiosity:
> Why does a domU have to support PAE? AFAIK the page
table is managed by
> the Hypervisor. Is the interface to the Hypervisor so
badly designed
> that it can't hide such details?

See messages in mail-index:port-xen for August 2006, with
the subject

    Xen3/PAE problems with domainU

There are some web link pointers to xen-users in that
thread.  What I
gathered from it without digging for major technical details
is that
the page tables are manipulated in a native-like format in
all
domains, so their structural layout must match in all
domains (PAE vs.
non-PAE).

>From a user's perspective, if you try to load a
non-PAE-capable domU
on a PAE host, xend will spit out EINVAL and refuse to
complete the
domain construction.

-- 
-- Todd Vierling <tvduh.org> <tvpobox.com> <toddvierling.name>

On 2/12/07, Todd Vierling <tvpobox.com> wrote:
> On 2/12/07, Matthias Scheler <tronzhadum.org.uk> wrote:
> > > Runs fine on a PAE mode 32-bit Linux host
that you do not have the
> > > option to reconfigure?
> >
> > Out of technical curiosity:
> > Why does a domU have to support PAE? AFAIK the
page table is managed by
> > the Hypervisor. Is the interface to the Hypervisor
so badly designed
> > that it can't hide such details?
>
> See messages in mail-index:port-xen for August 2006,
with the subject
>
>     Xen3/PAE problems with domainU
>
> There are some web link pointers to xen-users in that
thread.  What I
> gathered from it without digging for major technical
details is that
> the page tables are manipulated in a native-like format
in all
> domains, so their structural layout must match in all
domains (PAE vs.
> non-PAE).
>
> From a user's perspective, if you try to load a
non-PAE-capable domU
> on a PAE host, xend will spit out EINVAL and refuse to
complete the
> domain construction.

What about an AMD64 NetBSD domU kernel? 

On 2/12/07, Todd Vierling <tvpobox.com> wrote:
> On 2/12/07, Matthias Scheler <tronzhadum.org.uk> wrote:
> > > Runs fine on a PAE mode 32-bit Linux host
that you do not have the
> > > option to reconfigure?
> >
> > Out of technical curiosity:
> > Why does a domU have to support PAE? AFAIK the
page table is managed by
> > the Hypervisor. Is the interface to the Hypervisor
so badly designed
> > that it can't hide such details?
>
> See messages in mail-index:port-xen for August 2006,
with the subject
>
>     Xen3/PAE problems with domainU
>
> There are some web link pointers to xen-users in that
thread.  What I
> gathered from it without digging for major technical
details is that
> the page tables are manipulated in a native-like format
in all
> domains, so their structural layout must match in all
domains (PAE vs.
> non-PAE).
>
> From a user's perspective, if you try to load a
non-PAE-capable domU
> on a PAE host, xend will spit out EINVAL and refuse to
complete the
> domain construction.

What about an AMD64 NetBSD domU kernel? 

On 2/12/07, Felipe Alfaro Solana <felipe.alfarogmail.com> wrote:
> > From a user's perspective, if you try to load a
non-PAE-capable domU
> > on a PAE host, xend will spit out EINVAL and
refuse to complete the
> > domain construction.
>
> What about an AMD64 NetBSD domU kernel? 

Not on a "PAE" host, because a "PAE"
host is running 32-bit.  (Yes, I
know that amd64 uses the PAE table structure with more PTEs
in the
first level, but amd64 isn't normally referred to as a
"PAE" system.)

Unfortunately, 32-bit + PAE is by far the most commonly
deployed Xen
hosting setup.  So when the question is how to get NetBSD
running as a
domU when you don't have control over the host (mmm, virtual
server
hosting, the new commodity!), we're way behind the curve.

-- 
-- Todd Vierling <tvduh.org> <tvpobox.com> <toddvierling.name>

On 2/12/07, Felipe Alfaro Solana <felipe.alfarogmail.com> wrote:
> > From a user's perspective, if you try to load a
non-PAE-capable domU
> > on a PAE host, xend will spit out EINVAL and
refuse to complete the
> > domain construction.
>
> What about an AMD64 NetBSD domU kernel? 

Not on a "PAE" host, because a "PAE"
host is running 32-bit.  (Yes, I
know that amd64 uses the PAE table structure with more PTEs
in the
first level, but amd64 isn't normally referred to as a
"PAE" system.)

Unfortunately, 32-bit + PAE is by far the most commonly
deployed Xen
hosting setup.  So when the question is how to get NetBSD
running as a
domU when you don't have control over the host (mmm, virtual
server
hosting, the new commodity!), we're way behind the curve.

-- 
-- Todd Vierling <tvduh.org> <tvpobox.com> <toddvierling.name>