[Xen-ia64-devel] RE: A patch to remove dcr.63 for running_on_xen indicator

["Magenheimer, Dan (HP Labs Fort Collins)" <dan.magenheimer@xxxxxx>]

>       Is not xenlinux-ia64 accessing fixed address for shared 
> memory like following code from xenlinux-ia64?   This patch 
> just use same assumption.

Yes, there is code like this all over xenlinux.  But the code
that is missing in early_xen_setup looks like this: (pseudo-code)

if (running_on_xen) {
        if (hypercall_assign_shared_page_address(SHARED_PAGE_ADDR) !=
OK)
                panic("hypervisor rejects shared page address!\n");
}

So running_on_xen needs to be determined before the shared page
address is set.

>       If xenlinux support dynamic configurable share memory 
> address, this patch can simply be updated too.
>       
>       The reason to push this patch is that bit 63 of DCR may 
> be not reserved in future just like PSR.vm bit in VT-i spec. 
> Probing shared memory is just much safe.

While it is true that bit 63 of the DCR is architecturally
reserved, we will probably have several years of notice
if it is actually going to be architecturally-defined in
a future IPF implementation.  (If you know that it is
definitely going to be defined in an IPF chip before
2010, please let me know and we certainly can choose a
different bit.)

I intend to utilize dynamic configurable shared memory address
within the next 6-12 months.

Anyway, I am open to using another method (other than dcr bit 63)
to determine running_on_xen, but I am not open to defining a
fixed shared page address.

Dan

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