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xen-devel
Re: [Xen-devel] XENFEAT_writable_pagetables vs VMASST_TYPE_writable_page
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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