[PATCH v18 00/12] Support page table check on PowerPC

Andrew Donnellan
2025-12-18T17:10:11Z

[I will be leaving IBM in about a month from now, and will also be on leave
for most of that time starting tomorrow. I've cc'd my personal email, which
I am going to use for any kernel development I do after I leave, and also
Srish Srinivasan, who will be taking over some of my work.]

Support page table check on PowerPC. Page table check tracks the usage of
of page table entries at each level to ensure that anonymous mappings have
at most one writable consumer, and likewise that file-backed mappings are
not simultaneously also anonymous mappings.

In order to support this infrastructure, a number of helpers or stubs must be
defined or updated for all powerpc platforms. Additionally, we separate
set_pte_at() and set_pte_at_unchecked(), to allow for internal, uninstrumented
mappings.

On some PowerPC platforms, implementing {pte,pmd,pud}_user_accessible_page()
requires the address. We revert previous changes that removed the address
parameter from various interfaces, and add it to some other interfaces,
in order to allow this.

For now, we don't allow page table check alongside HUGETLB_PAGE, due to the
arch-specific complexity of set_huge_page_at(). (I'm sure I could figure
this out, but I have to get this version on this list before I leave my job.)

This series was initially written by Rohan McLure, who has left IBM and
is no longer working on powerpc.

v18:
* Rebase on mm-new
* Add instrumentation for pudp_invalidate()
* Add cleanup patch to use pte_advance_pfn()
* Move p{m,u}d_user_accessible_page() to a more sensible place in the code
* Disable when HUGETLB_PAGE is enabled

v17:
* Rebase on mm-new to fix build failure on commit 3f3806eff23f ("riscv: use an
atomic xchg in pudp_huge_get_and_clear()")
* Remove patch 10 ("powerpc: mm: Add pud_pfn() stub"), as the original
reasoning for the stub is now wrong (pud_pfn() is now used more broadly in
generic code, and commit 35a76f5c0863 ("mm/arch: provide pud_pfn()
fallback") now provides a generic fallback. This fixes the build failure on
some powerpc platforms (0day)
Link: https://lore.kernel.org/all/20250909091335.183439-1-ajd@linux.ibm.com/

v16:
* Rebase on mainline
Link: https://lore.kernel.org/all/20250813062614.51759-1-ajd@linux.ibm.com/

v15:
* Rebase on mainline, including commit 91e40668e70a
("mm/page_table_check: Batch-check pmds/puds just like ptes") and
associated arm64 changes
* Clarify/fix some commit messages
* Fix handling of address in a loop in __page_table_check_ptes_set()
Link: https://lore.kernel.org/all/20250625063753.77511-1-ajd@linux.ibm.com/

v14:
* Fix a call to page_table_check_pud_set() that was missed (akpm)
Link: https://lore.kernel.org/all/20250411054354.511145-1-ajd@linux.ibm.com/

v13:
* Rebase on mainline
* Don't use set_pte_at_unchecked() for early boot purposes (Pasha)
Link: https://lore.kernel.org/linuxppc-dev/20250211161404.850215-1-ajd@linux.ibm.com/

v12:
* Rename commits that revert changes to instead reflect that we are
reinstating old behaviour due to it providing more flexibility
* Add return line to pud_pfn() stub
* Instrument ptep_get_and_clear() for nohash
Link: https://lore.kernel.org/linuxppc-dev/20240402051154.476244-1-rmclure@linux.ibm.com/

v11:
* The pud_pfn() stub, which previously had no legitimate users on any
powerpc platform, now has users in Book3s64 with transparent pages.
Include a stub of the same name for each platform that does not
define their own.
* Drop patch that standardised use of p*d_leaf(), as already included
upstream in v6.9.
* Provide fallback definitions of p{m,u}d_user_accessible_page() that
do not reference p*d_leaf(), p*d_pte(), as they are defined after
powerpc/mm headers by linux/mm headers.
* Ensure that set_pte_at_unchecked() has the same checks as
set_pte_at().
Link: https://lore.kernel.org/linuxppc-dev/20240328045535.194800-14-rmclure@linux.ibm.com/

v10:
* Revert patches that removed address and mm parameters from page table
check routines, including consuming code from arm64, x86_64 and
riscv.
* Implement *_user_accessible_page() routines in terms of pte_user()
where available (64-bit, book3s) but otherwise by checking the
address (on platforms where the pte does not imply whether the
mapping is for user or kernel)
* Internal set_pte_at() calls replaced with set_pte_at_unchecked(), which
is identical, but prevents double instrumentation.
Link: https://lore.kernel.org/linuxppc-dev/20240313042118.230397-9-rmclure@linux.ibm.com/T/

v9:
* Adapt to using the set_ptes() API, using __set_pte_at() where we need
must avoid instrumentation.
* Use the logic of *_access_permitted() for implementing
*_user_accessible_page(), which are required routines for page table
check.
* Even though we no longer need p{m,u,4}d_leaf(), still default
implement these to assist in refactoring out extant
p{m,u,4}_is_leaf().
* Add p{m,u}_pte() stubs where asm-generic does not provide them, as
page table check wants all *user_accessible_page() variants, and we
would like to default implement the variants in terms of
pte_user_accessible_page().
* Avoid the ugly pmdp_collapse_flush() macro nonsense! Just instrument
its constituent calls instead for radix and hash.
Link: https://lore.kernel.org/linuxppc-dev/20231130025404.37179-2-rmclure@linux.ibm.com/

v8:
* Fix linux/page_table_check.h include in asm/pgtable.h breaking
32-bit.
Link: https://lore.kernel.org/linuxppc-dev/20230215231153.2147454-1-rmclure@linux.ibm.com/

v7:
* Remove use of extern in set_pte prototypes
* Clean up pmdp_collapse_flush macro
* Replace set_pte_at with static inline function
* Fix commit message for patch 7
Link: https://lore.kernel.org/linuxppc-dev/20230215020155.1969194-1-rmclure@linux.ibm.com/

v6:
* Support huge pages and p{m,u}d accounting.
* Remove instrumentation from set_pte from kernel internal pages.
* 64s: Implement pmdp_collapse_flush in terms of __pmdp_collapse_flush
as access to the mm_struct * is required.
Link: https://lore.kernel.org/linuxppc-dev/20230214015939.1853438-1-rmclure@linux.ibm.com/

v5: https://lore.kernel.org/linuxppc-dev/20221118002146.25979-1-rmclure@linux.ibm.com/

---
Andrew Donnellan (2):
arm64/mm: Add addr parameter to __set_ptes_anysz()
arm64/mm: Add addr parameter to __ptep_get_and_clear_anysz()

Rohan McLure (10):
mm/page_table_check: Reinstate address parameter in [__]page_table_check_pud[s]_set()
mm/page_table_check: Reinstate address parameter in [__]page_table_check_pmd[s]_set()
mm/page_table_check: Provide addr parameter to page_table_check_ptes_set()
mm/page_table_check: Reinstate address parameter in [__]page_table_check_pud_clear()
mm/page_table_check: Reinstate address parameter in [__]page_table_check_pmd_clear()
mm/page_table_check: Reinstate address parameter in [__]page_table_check_pte_clear()
mm: Provide address parameter to p{te,md,ud}_user_accessible_page()
powerpc/mm: Implement *_user_accessible_page() for ptes
powerpc/mm: Use set_pte_at_unchecked() for internal usages
powerpc/mm: Support page table check

arch/arm64/include/asm/pgtable.h | 46 +++++++++----------
arch/arm64/mm/hugetlbpage.c | 17 +++----
arch/powerpc/Kconfig | 1 +
arch/powerpc/include/asm/book3s/32/pgtable.h | 12 ++++-
arch/powerpc/include/asm/book3s/64/pgtable.h | 62 +++++++++++++++++++++----
arch/powerpc/include/asm/nohash/pgtable.h | 13 +++++-
arch/powerpc/include/asm/pgtable.h | 10 ++++
arch/powerpc/mm/book3s64/hash_pgtable.c | 4 ++
arch/powerpc/mm/book3s64/pgtable.c | 25 ++++++----
arch/powerpc/mm/book3s64/radix_pgtable.c | 9 ++--
arch/powerpc/mm/pgtable.c | 12 +++++
arch/riscv/include/asm/pgtable.h | 22 ++++-----
arch/x86/include/asm/pgtable.h | 22 ++++-----
include/linux/page_table_check.h | 69 ++++++++++++++++------------
include/linux/pgtable.h | 10 ++--
mm/page_table_check.c | 41 +++++++++--------
16 files changed, 245 insertions(+), 130 deletions(-)
---
base-commit: c224625ec6f8a0476ffffc09807f4d717ba9cc93
change-id: 20251105-pgtable_check_v18rebase-2a8f88819994

--
Andrew Donnellan OzLabs, ADL Canberra
ajd@linux.ibm.com IBM Australia Limited