[Xen-devel] Re: about fixup_page_fault

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 17/12/2008 11:04, "Tim Deegan" <Tim.Deegan@xxxxxxxxxx> wrote:

>>> At 09:04 +0000 on 17 Dec (1229504644), Keir Fraser wrote:
>>>> A Xen fault shouldn't cause a lookup in guest tables for HVM guests.
>>> 
>>> Looks like it does, though. :(  The check in fixup_page_fault should
>>> probably be more like:
>> 
>> But wouldn't this just cause an infinite loop?
> 
> I thought that was what Kevin was reporting.

Oh yes, so he was. Duh. :-)

>> Since shadow code would fix up the fault in the guest shadow tables,
>> which the hypervisor is not running on?
> 
> Yes, exactly.  But it would only do that for faulting accesses from Xen
> that (a) weren't fixed up by any of the other mechanism, and (b)
> happened to be to addresses that were mapped in the guest tables.  And
> Xen would never do such a thing. :)

I certainly think that something like the patch you proposed would cause a
better failure mode.

Kevin: Can you try out what Tim proposed and if it indeed makes things
better (at least, you get a proper crash!) we should get that checked in.

 -- Keir



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