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

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Message-ID: <20250905055103.3821518-3-baolu.lu@linux.intel.com>
Date: Fri,  5 Sep 2025 13:50:57 +0800
From: Lu Baolu <baolu.lu@...ux.intel.com>
To: Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>,
	Kevin Tian <kevin.tian@...el.com>,
	Jason Gunthorpe <jgg@...dia.com>,
	Jann Horn <jannh@...gle.com>,
	Vasant Hegde <vasant.hegde@....com>,
	Dave Hansen <dave.hansen@...el.com>,
	Alistair Popple <apopple@...dia.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Jean-Philippe Brucker <jean-philippe@...aro.org>,
	Andy Lutomirski <luto@...nel.org>,
	Yi Lai <yi1.lai@...el.com>
Cc: iommu@...ts.linux.dev,
	security@...nel.org,
	linux-kernel@...r.kernel.org,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Lu Baolu <baolu.lu@...ux.intel.com>
Subject: [PATCH v4 2/8] mm: Actually mark kernel page table pages

From: Dave Hansen <dave.hansen@...ux.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@...ux.intel.com>
Signed-off-by: Lu Baolu <baolu.lu@...ux.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