[Xen-devel] Re: [XenPPC] dom0 auto-translate mmap()

[Jimi Xenidis <jimix@xxxxxxxxxxxxxx>]

BTW: there was a quick discussion on this before:
  http://lists.xensource.com/archives/html/xen-devel/2006-11/ 
msg00672.html
IIRC, We we continued "faking it out" until we got the ability to  
mmap'ing arbitrary pages.
Now that we fixed the ability to properly address "remote" memory,  
this should be easy enough.
-JX

On Jun 11, 2007, at 12:42 PM, Hollis Blanchard wrote:

> Hi, as I'm porting the PPC patches to the current Linux tree, I  
> noticed
> this code in privcmd.c:
>
>         static int privcmd_mmap(struct file * file, struct  
> vm_area_struct * vma)
>         {
>                 /* Unsupported for auto-translate guests. */
>                 if (xen_feature(XENFEAT_auto_translated_physmap))
>                         return -ENOSYS;
>
>                 ... allow mmap to succeed ...
>         }
>
> All addresses provided to Xen by an autotranslate guest are guest
> physical addresses, which Xen then translates to machine: (domid,  
> gpfn)
> -> (mfn). The problem is that dom0 actually needs to address memory
> outside of its own domain allocation, but how can you distinguish a  
> gpfn
> from an mfn in this case?
>
> PowerPC runs all domains, including dom0, in "autotranslate mode", and
> so we have a workaround for this problem. When we know we're trying to
> map machine addresses (which is what the builder tools do), we simply
> set the high bit in "pfn" before passing it down to Xen. Xen then  
> knows
> it's a machine address.
>
> This limits autotranslate domains to 32 + 12 - 1 = 43 bits of address
> space, which I think is reasonable, especially since most "64-bit"
> processors don't use many more bits than that anyways...
>
>
>
> The net is that I would like to remove the above test. I wonder why it
> was added in the first place? Somebody has a privileged autotranslate
> domain and mistakenly tried to run the domain building tools?
>
> --
> Hollis Blanchard
> IBM Linux Technology Center
>
>
> _______________________________________________
> Xen-ppc-devel mailing list
> Xen-ppc-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-ppc-devel

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel