Re: [Xen-devel] Shadow pagetable code changes since 3.0.2

[Yongjun Jeon <yongjunj@xxxxxxxxxxxxxx>]

Thanks for your response; I just saw it.

Just one more question: Do you know of any updated documentation, besides 
what's on the Cambridge website 
(http://www.cl.cam.ac.uk/research/srg/netos/xen/documentation.html)?
Thanks,
Jun

On Wed, 11 Jul 2007, Tim Deegan wrote:

> At 16:02 -0400 on 09 Jul (1183996971), Yongjun Jeon wrote:
> > I noticed that the shadow pagetable code has went through some serious
> > design change since 3.0.2, and I couldn't find a good documentation that
> > explains how the old code maps to the new code.
> >
> > Can anyone please explain the exact nature of the change - how the new
> > functions replace the old ones?
> The architecture of the shadow code changed considerably after 3.0.2; I
> doubt you will have much luck porting that patchset directly.
> The major change is that instead of "unhooking" shadow pages from the
> hierarchy when a guest writes to a pagetable, and re-syncing the shadow
> to the pagetable afterwards, we trap and emulate writes to pagetables,
> synchronously updating the shadows as we go.  But also the way shadow
> pagetables are allocated, tracked, protected and destroyed have
> changed.
>
> Most of the moving parts of the shadow code (including the shadow lock)
> are now private to the arch/x86/mm/shadow directory.  Outside callers
> use the functions in asm-x86/paging.h, which dispatch to shadow code or
> to hardware paging assistance as appropriate.
>
> The p2m table is now organised as a pagetable, and managed by
> arch/x86/mm/p2m.c I expect that most of the changes you will want to
> make are in there; changes to the p2m map are reflected automatically in
> the shadow pagetables by the callback to paging_write_p2m_entry().
>
> For data pages, the function sh_get_page_from_l1e() handles reference
> counting and will need to know about the extra domain ID used.  For
> pagetable pages, shadow_promote() still exists and would be a good place
> to make sure the promoted page is not copy-on-write.
>
> Tim.
>
> --
> Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, XenSource UK Limited
> Registered office c/o EC2Y 5EB, UK; company number 05334508
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