Re: [Xen-devel] Writable page tables

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 6 Apr 2006, at 22:50, Ky Srinivasan wrote:

> I have a question with regards to writable page table support. I am 
> able
> to modify a page table entry via the hypercall interface
> (xen_l1_entry_update). However, if I enable the writable page table
> feature, the hypervisor fails to fix up the write fault on the same 
> page
> table. The fixup fails in ptwr_do_page_fault() - the problem appears to
> be with the TYPE_COUNT  (it is 0 and all other checks pass). Why is the
> writable code path more restrictive, given that the modifications done
> via the writable path will be validated by the hypervisor before 
> hooking
> in the page table under question. Since the validation is deferred, I
> was expecting this path would have fewer checks.
Have you write protected the page but not yet pinned it as a pagetable 
page, nor hooked it into an existing pagetable?
 -- Keir


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