[Xen-devel] Re: about fixup_page_fault

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 17/12/2008 08:32, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

>> Consider copy_from_guest() applied to a PV guest with dirty
>> logging enabled.
>> The #PF handler should fix up faults when accessing guest
>> address space via
>> shadow page tables, even when the access happens within Xen.
> 
> If Xen access guest address space intentionally like a hypercall
> parameter, such fix up is desired. However what about an random
> illegal access in Xen with faulting address happening to fall into
> guest address space?

Well, HVM guests obviously have a separate address space, so no issue there.
For a PV guest -- yes, Xen will then erroneously access guest address space
instead of crashing. But this is no worse than what would happen if running
without shadow page tables (i.e., dirty logging disabled). Fortunately Xen
has no bugs. ;-)

 -- Keir



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