[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH] Solved the Xen PV/KASLR riddle

On 08/29/2014 04:55 PM, Konrad Rzeszutek Wilk wrote:
On Fri, Aug 29, 2014 at 03:44:06PM +0100, Jan Beulich wrote:
On 29.08.14 at 16:27, <stefan.bader@xxxxxxxxxxxxx> wrote:
Sure. Btw, someone also contacted me saying they have the same problem
changing the layout but having really big initrd (500M). While that feels
it should be impossible (if the kernel+initrd+xen stuff has to fix the 512M
kernel image size area then). But if it can happen, then surely it does
mappings to be where the module space starts then.

Since the initrd doesn't really need to be mapped into the (limited)
virtual address space a pv guest starts with, we specifically got

  * Whether or not the guest can deal with being passed an initrd not
  * mapped through its initial page tables.

to deal with that situation. The hypervisor side for Dom0 is in place,
and the kernel side works in our (classic) kernels. Whether it got
implemented for DomU meanwhile I don't know; I'm pretty certain
pv-ops kernels don't support it so far.

Correct - Not implemented. Here is what I had mentioned in the past:
(see http://lists.xen.org/archives/html/xen-devel/2014-03/msg00580.html)

     at that but I can't figure out a nice way of implementing this
     without the usage of SPARSEMAP_VMAP virtual addresses - which is how
     the classic Xen does it. But then - I don't know who is using huge PV
     guests - as the PVHVM does a fine job? But then with PVH, now you can
     boot with large amount of memory (1TB?) - so some of these issues
     would go away? Except the 'large ramdisk' as that would eat in the
     MODULES_VADDR I think? Needs more thinking.

.. and then I left it and to my suprise saw on Luis's slides that
Jurgen is going to take a look at that (500GB support).

I have a patch which should do the job. It is based on the classic
kernel patch Jan mentioned above. The system is coming up with it, I
haven't tested it with a huge initrd up to now. My plan was to post the
patch together with the rest of the >500GB support, but I can send it
on it's own if required.


Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.