Re: [Xen-devel] [PATCH RFC 2/2] xen/pvh: enable mmu_update hypercall

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.10.14 at 09:53, <tim@xxxxxxx> wrote:
> At 12:53 +0200 on 15 Oct (1413374025), Roger Pau Monne wrote:
>> This is needed for performing save/restore of PV guests.
> 
> On IRC I suggested that this would be OK as long as there were other
> checks to make sure that the target of all these ops is PV (in
> particular that a PVH/HVM guest can't end up calling PV MM operations
> on itself).

And not just that - I can't even see how this would work at present:
paging_write_guest_entry() uses
v->arch.paging.mode->write_guest_entry, yet that actor gets filled
by shadow code only. I don't currently see how for PVH, requiring
HAP, this wouldn't end up in NULL dereferences. Am I overlooking
some (non-grep-able) initialization of this and .cmpxchg_guest_entry?

Jan


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