Re: where is writable page table implemented?

[weiming <zephyr.zhao@gmail.com>]

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Hi Tim,

Do you know under which situation we use writable page table instead of
calling update_va_mapping?

And do you know the purpose of the counter defined in
page_info.u.in_use.type_info?
I understand that xen needs to keep track of the type of each page
(L1_page_table_page, L2_page_table_page, pinned, unpinned, validated, etc),
but why do we need to use the lower 26 bits of "type_info" as a counter? (in
"get_page_type()", the counter is increased. )  Similarly,  get_page() /
put_page() also increases/decreases the page.count_info. Could you please
give me some hint about the usage of such counters?

Thanks a lot!
Weiming


On Tue, Apr 1, 2008 at 4:38 AM, Tim Deegan <Tim.Deegan@citrix.com> wrote:

> At 19:43 -0400 on 30 Mar (1206906207), weiming wrote:
> > with writable page table, why guest os still calls update_va_mapping to
> > update the pte?
>
> It's faster to call into Xen with an explicit modification, or a list of
> them, than to have xen trap and do a full x86 instruction emaulation to
> figure out what you werere doing.
>
> Cheers,
>
> Tim.
>
> --
> Tim Deegan <Tim.Deegan@citrix.com>
> Principal Software Engineer, Citrix Systems (R&D) Ltd.
> [Company #02300071, SL9 0DZ, UK.]
>

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