Re: [Xen-devel] where is writable page table implemented?

[weiming <zephyr.zhao@xxxxxxxxx>]

Hi Tim,

Thanks a lot!

Now, I know that fixup_page_fault() -> ptwr_do_page_fault handles the write attempts to a pagetable page.

But 
1) how does the guest OS tell xen which page is a pagetable page?  What if the guest doesn't do so? I assume xen should check if a pagetable had already been registered or not. But in do_mmuext_op(), there is no such check before setting the cr3.

2) in ptwr_do_page_fault(), it should disconnect the page from page directory and then mark the page as writable.  Where are they done? In x86_emulate()?

Thanks in advance!
Weiming

On Mon, Mar 24, 2008 at 12:25 PM, Tim Deegan <Tim.Deegan@xxxxxxxxxx> wrote:

At 12:18 -0400 on 24 Mar (1206361139), weiming wrote:
> Hi,
>
> I want to read the code about the implementation of writable page table. But
> I can't find it in the source codes.

xen/arch/x86/mm.c, the functions after the comment "Writable Pagetables"
(ptwr_*)

The guest is responsible for revoking write access to its own
pagetables, but that is checked by the recursive pagetable walk started
by the MMUEXT_PIN_* hypercall.

Cheers,

Tim.

--
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Citrix Systems (R&D) Ltd.
[Company #02300071, SL9 0DZ, UK.]

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