+ mm-call-ctor-dtor-for-kernel-ptes.patch added to mm-new branch

+ mm-call-ctor-dtor-for-kernel-ptes.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm: call ctor/dtor for kernel PTEs
has been added to the -mm mm-new branch.  Its filename is
     mm-call-ctor-dtor-for-kernel-ptes.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-call-ctor-dtor-for-kernel-ptes.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Kevin Brodsky <kevin.brodsky@arm.com>
Subject: mm: call ctor/dtor for kernel PTEs
Date: Tue, 8 Apr 2025 10:52:13 +0100

Since [1], constructors/destructors are expected to be called for all page
table pages, at all levels and for both user and kernel pgtables.  There
is however one glaring exception: kernel PTEs are managed via separate
helpers (pte_alloc_kernel/pte_free_kernel), which do not call the [cd]tor,
at least not in the generic implementation.

The most obvious reason for this anomaly is that init_mm is special-cased
not to use split page table locks.  As a result calling ptlock_init() for
PTEs associated with init_mm would be wasteful, potentially resulting in
dynamic memory allocation.  However, pgtable [cd]tors perform other
actions - currently related to accounting/statistics, and potentially more
functionally significant in the future.

Now that pagetable_pte_ctor() is passed the associated mm, we can make it
skip the call to ptlock_init() for init_mm; this allows us to call the
ctor from pte_alloc_one_kernel() too.  This is matched by a call to the
pgtable destructor in pte_free_kernel(); no special-casing is needed on
that path, as ptlock_free() is already called unconditionally. 
(ptlock_free() is a no-op unless a ptlock was allocated for the given
PTP.)

This patch ensures that all architectures that rely on
<asm-generic/pgalloc.h> call the [cd]tor for kernel PTEs. 
pte_free_kernel() cannot be overridden so changing the generic
implementation is sufficient.  pte_alloc_one_kernel() can be overridden
using __HAVE_ARCH_PTE_ALLOC_ONE_KERNEL, and a few architectures implement
it by calling the page allocator directly.  We amend those so that they
call the generic __pte_alloc_one_kernel() instead, if possible, ensuring
that the ctor is called.

A few architectures do not use <asm-generic/pgalloc.h>; those will be
taken care of separately.

[1] https://lore.kernel.org/linux-mm/20250103184415.2744423-1-kevin.brodsky@arm.com/

Link: https://lkml.kernel.org/r/20250408095222.860601-4-kevin.brodsky@arm.com
Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Linus Waleij <linus.walleij@linaro.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Matthew Wilcow (Oracle) <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: <x86@kernel.org>
Cc: Yang Shi <yang@os.amperecomputing.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 arch/csky/include/asm/pgalloc.h |    2 +-
 arch/microblaze/mm/pgtable.c    |    2 +-
 arch/openrisc/mm/ioremap.c      |    2 +-
 include/asm-generic/pgalloc.h   |    7 ++++++-
 include/linux/mm.h              |    2 +-
 5 files changed, 10 insertions(+), 5 deletions(-)

--- a/arch/csky/include/asm/pgalloc.h~mm-call-ctor-dtor-for-kernel-ptes
+++ a/arch/csky/include/asm/pgalloc.h
@@ -29,7 +29,7 @@ static inline pte_t *pte_alloc_one_kerne
 	pte_t *pte;
 	unsigned long i;
 
-	pte = (pte_t *) __get_free_page(GFP_KERNEL);
+	pte = __pte_alloc_one_kernel(mm);
 	if (!pte)
 		return NULL;
 
--- a/arch/microblaze/mm/pgtable.c~mm-call-ctor-dtor-for-kernel-ptes
+++ a/arch/microblaze/mm/pgtable.c
@@ -245,7 +245,7 @@ unsigned long iopa(unsigned long addr)
 __ref pte_t *pte_alloc_one_kernel(struct mm_struct *mm)
 {
 	if (mem_init_done)
-		return (pte_t *)__get_free_page(GFP_KERNEL | __GFP_ZERO);
+		return __pte_alloc_one_kernel(mm);
 	else
 		return memblock_alloc_try_nid(PAGE_SIZE, PAGE_SIZE,
 					      MEMBLOCK_LOW_LIMIT,
--- a/arch/openrisc/mm/ioremap.c~mm-call-ctor-dtor-for-kernel-ptes
+++ a/arch/openrisc/mm/ioremap.c
@@ -36,7 +36,7 @@ pte_t __ref *pte_alloc_one_kernel(struct
 	pte_t *pte;
 
 	if (likely(mem_init_done)) {
-		pte = (pte_t *)get_zeroed_page(GFP_KERNEL);
+		pte = __pte_alloc_one_kernel(mm);
 	} else {
 		pte = memblock_alloc_or_panic(PAGE_SIZE, PAGE_SIZE);
 	}
--- a/include/asm-generic/pgalloc.h~mm-call-ctor-dtor-for-kernel-ptes
+++ a/include/asm-generic/pgalloc.h
@@ -23,6 +23,11 @@ static inline pte_t *__pte_alloc_one_ker
 
 	if (!ptdesc)
 		return NULL;
+	if (!pagetable_pte_ctor(mm, ptdesc)) {
+		pagetable_free(ptdesc);
+		return NULL;
+	}
+
 	return ptdesc_address(ptdesc);
 }
 #define __pte_alloc_one_kernel(...)	alloc_hooks(__pte_alloc_one_kernel_noprof(__VA_ARGS__))
@@ -48,7 +53,7 @@ static inline pte_t *pte_alloc_one_kerne
  */
 static inline void pte_free_kernel(struct mm_struct *mm, pte_t *pte)
 {
-	pagetable_free(virt_to_ptdesc(pte));
+	pagetable_dtor_free(virt_to_ptdesc(pte));
 }
 
 /**
--- a/include/linux/mm.h~mm-call-ctor-dtor-for-kernel-ptes
+++ a/include/linux/mm.h
@@ -3133,7 +3133,7 @@ static inline void pagetable_dtor_free(s
 static inline bool pagetable_pte_ctor(struct mm_struct *mm,
 				      struct ptdesc *ptdesc)
 {
-	if (!ptlock_init(ptdesc))
+	if (mm != &init_mm && !ptlock_init(ptdesc))
 		return false;
 	__pagetable_ctor(ptdesc);
 	return true;
_

Patches currently in -mm which might be from kevin.brodsky@arm.com are

mm-pass-mm-down-to-pagetable_ptepmd_ctor.patch
x86-pgtable-always-use-pte_free_kernel.patch
mm-call-ctor-dtor-for-kernel-ptes.patch
m68k-mm-call-ctor-dtor-for-kernel-ptes.patch
powerpc-mm-call-ctor-dtor-for-kernel-ptes.patch
sparc64-mm-call-ctor-dtor-for-kernel-ptes.patch
mm-skip-ptlock_init-for-kernel-pmds.patch
arm64-mm-use-enum-to-identify-pgtable-level-instead-of-_shift.patch
arm64-mm-always-call-pte-pmd-ctor-in-__create_pgd_mapping.patch
riscv-mm-clarify-ctor-mm-argument-in-alloc_ptepmd_late.patch
arm64-mm-call-pud-p4d-ctor-in-__create_pgd_mapping.patch
riscv-mm-call-pud-p4d-ctor-in-special-kernel-pgtable-alloc.patch