Re: [Xen-devel] XENFEAT_writable_pagetables vs VMASST_TYPE_writable_pagetables

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 31 May 2006, at 15:22, Jacob Gorm Hansen wrote:

> I am trying to figure out what the difference is between calling
> vm-assist to enable writable page tables, and what the xen-feature
> with the same name does. The former is enabled, while the latter
> returns false. This has the effect that the various checks from
> changeset 9243:f00e257d200c fail and pages are still pinned/unpinned,
> but things still seem to work. This is with my own domain builder
> using libxc.
>
> So what is the story when combining VMASST_ and XENFEAT_?
It's a case of really bad naming: XENFEAT_writable_pagetables means 
that none of the pagetables need to be write-protected or pinned 
(presumably because you are permanently on shadow page tables). Whereas 
the vmassist simply means that you can attempt to directly write to 
your bottom-level PTEs, but page tables must generally be pinned and 
write-protected.
 -- Keir


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