[PATCH v4 2/8] mm: Actually mark kernel page table pages

Lu Baolu
2025-09-05T05:53:22Z

From: Dave Hansen <dave.hansen@linux.intel.com>

Now that the API is in place, mark kernel page table pages just
after they are allocated. Unmark them just before they are freed.

Note: Unconditionally clearing the 'kernel' marking (via
ptdesc_clear_kernel()) would be functionally identical to what
is here. But having the if() makes it logically clear that this
function can be used for kernel and non-kernel page tables.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
include/asm-generic/pgalloc.h | 18 ++++++++++++++++++
include/linux/mm.h | 3 +++
2 files changed, 21 insertions(+)

diff --git a/include/asm-generic/pgalloc.h b/include/asm-generic/pgalloc.h
index 3c8ec3bfea44..b9d2a7c79b93 100644
--- a/include/asm-generic/pgalloc.h
+++ b/include/asm-generic/pgalloc.h
@@ -28,6 +28,8 @@ static inline pte_t *__pte_alloc_one_kernel_noprof(struct mm_struct *mm)
return NULL;
}

+ ptdesc_set_kernel(ptdesc);
+
return ptdesc_address(ptdesc);
}
#define __pte_alloc_one_kernel(...) alloc_hooks(__pte_alloc_one_kernel_noprof(__VA_ARGS__))
@@ -146,6 +148,10 @@ static inline pmd_t *pmd_alloc_one_noprof(struct mm_struct *mm, unsigned long ad
pagetable_free(ptdesc);
return NULL;
}
+
+ if (mm == &init_mm)
+ ptdesc_set_kernel(ptdesc);
+
return ptdesc_address(ptdesc);
}
#define pmd_alloc_one(...) alloc_hooks(pmd_alloc_one_noprof(__VA_ARGS__))
@@ -179,6 +185,10 @@ static inline pud_t *__pud_alloc_one_noprof(struct mm_struct *mm, unsigned long
return NULL;

pagetable_pud_ctor(ptdesc);
+
+ if (mm == &init_mm)
+ ptdesc_set_kernel(ptdesc);
+
return ptdesc_address(ptdesc);
}
#define __pud_alloc_one(...) alloc_hooks(__pud_alloc_one_noprof(__VA_ARGS__))
@@ -233,6 +243,10 @@ static inline p4d_t *__p4d_alloc_one_noprof(struct mm_struct *mm, unsigned long
return NULL;

pagetable_p4d_ctor(ptdesc);
+
+ if (mm == &init_mm)
+ ptdesc_set_kernel(ptdesc);
+
return ptdesc_address(ptdesc);
}
#define __p4d_alloc_one(...) alloc_hooks(__p4d_alloc_one_noprof(__VA_ARGS__))
@@ -277,6 +291,10 @@ static inline pgd_t *__pgd_alloc_noprof(struct mm_struct *mm, unsigned int order
return NULL;

pagetable_pgd_ctor(ptdesc);
+
+ if (mm == &init_mm)
+ ptdesc_set_kernel(ptdesc);
+
return ptdesc_address(ptdesc);
}
#define __pgd_alloc(...) alloc_hooks(__pgd_alloc_noprof(__VA_ARGS__))
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 1ae97a0b8ec7..f3db3a5ebefe 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2895,6 +2895,9 @@ static inline void pagetable_free(struct ptdesc *pt)
{
struct page *page = ptdesc_page(pt);

+ if (ptdesc_test_kernel(pt))
+ ptdesc_clear_kernel(pt);
+
__free_pages(page, compound_order(page));
}

--
2.43.0