On Sat, Feb 18, 2023 at 01:14:04PM -0800, Rick Edgecombe wrote:

The x86 Control-flow Enforcement Technology (CET) feature includes a new
type of memory called shadow stack. This shadow stack memory has some
unusual properties, which requires some core mm changes to function
properly.

One of these changes is to allow for pmd_mkwrite() to create different
types of writable memory (the existing conventionally writable type and
also the new shadow stack type). Future patches will convert pmd_mkwrite()
to take a VMA in order to facilitate this, however there are places in the
kernel where pmd_mkwrite() is called outside of the context of a VMA.
These are for kernel memory. So create a new variant called
pmd_mkwrite_kernel() and switch the kernel users over to it. Have
pmd_mkwrite() and pmd_mkwrite_kernel() be the same for now. Future patches
will introduce changes to make pmd_mkwrite() take a VMA.

Only do this for architectures that need it because they call pmd_mkwrite()
in arch code without an associated VMA. Since it will only currently be
used in arch code, so do not include it in arch_pgtable_helpers.rst.

Cc: linux-kernel@vger.kernel.org
Cc: linux-s390@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: linux-mm@kvack.org
Tested-by: Pengfei Xu <redacted>
Suggested-by: David Hildenbrand <redacted>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>

Yup, 1:1 refactor.

Reviewed-by: Kees Cook <redacted>

-- 
Kees Cook