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

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

I dug back through my email to find this as I remembered
having a concern when I first glanced at it...

Although it is not implemented now for Xen/ia64,
vBlades allowed the guest to choose the (virtual)
location of the shared page.   This can be useful
as some guest OS's may already use the virtual
addresses currently "reserved" for the shared page
in the current Xen/ia64 implementation.  Also,
one can conceive of reasons why different guests
might have different shared pages (e.g. to allow
domain0 and domU's to be coresident in virtual
address space).

So, I don't think a guest should probe a fixed
virtual address as the mechanism to determine if
it is running_on_xen.

> -----Original Message-----
> From: Dong, Eddie [mailto:eddie.dong@xxxxxxxxx] 
> Sent: Monday, August 15, 2005 10:21 PM
> To: Magenheimer, Dan (HP Labs Fort Collins)
> Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
> Subject: A patch to remove dcr.63 for running_on_xen indicator
> 
> Dan:
>       The attached patch is target to remove dcr.63 bit usage to
> indicate running_on_xen or not, thus avoid future IPF spec violation
> (reserve bits should be 0 base on spec).
>       Please comments.
>       BTW, currnet XENLinux tree (yesterday) can't run on native
> environment for some reason. So I only test that on XEN environment.
> Eddie
> 
> 
> 
> diff -r 84356b86adf0 arch/ia64/xen/xensetup.S
> --- a/arch/ia64/xen/xensetup.S        Fri Aug 12 21:15:45 2005
> +++ b/arch/ia64/xen/xensetup.S        Mon Aug 15 18:44:21 2005
> @@ -16,12 +16,17 @@
>  
>       .text
>  GLOBAL_ENTRY(early_xen_setup)
> -     mov r8=cr.dcr;;
> -     extr.u r8=r8,63,1
> +     rsm psr.ic
> +     movl r9=XSI_BASE;;
> +     ld8.s r8=[r9];;
> +     tnat.nz.unc p6,p7=r8    // p6=1: No share memory
> +(p6) mov r8=0
> +(p7) mov r8=1                // on XEN
>       movl r9=running_on_xen;;
>       st4 [r9]=r8;;
> -     cmp.ne p7,p0=r8,r0;;
>  (p7) movl r10=xen_ivt;;
>  (p7) mov cr.iva=r10
> +     ssm psr.ic
> +     srlz.d
>       br.ret.sptk.many rp;;
>  END(xen_init)
> 

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