Re: Interaction between Xen and XFS: stray RW mappings

Jeremy Fitzhardinge
2007-10-22T18:37:59Z

Nick Piggin wrote:
> You could call it a bug I think. I don't know much about Xen though,
> whether or not it expects to be able to run an arbitrary OS kernel.
>

Xen's paravirtualized mode always requires a guest OS to be modified;
certainly some operating systems would be very hard to make work with
Xen. But you can always fall back to using shadow pagetables or full
hvm (VT/SVM) mode.

> Presumably, the hypervisor _could_ write protect and trap writes to
> *all* page table page mappings.
>

Xen manages this stuff with refcounts; it doesn't maintain an rmap for
these pages, so it would have to exhaustively search to do this. But
aside from that, Xen never actively modifies pagetables, so this would
be a new behaviour in the interface.

J