[PATCH 22/22] riscv: mm: drop ctor/dtor calls for kernel page tables

From: Kevin Brodsky <hidden>
Date: 2026-07-14 14:08:03
Also in: linux-arch, linux-efi, linux-mm, linux-riscv, linux-s390, linux-um, lkml, loongarch, sparclinux
Reply to: Kevin Brodsky, 2026-07-14

Thanks to recent changes:

* pagetable_*_ctor() and pagetable_dtor() do nothing for kernel page
  tables.

* efi_mm is also treated like a kernel mm by the page table logic,
  including ctors.

We can therefore drop the calls to ctors when allocating special
kernel page tables in mmu.c, as well as the dtor call when freeing
hotplug page tables.

The alloc_*_late() helpers are all identical after removing the ctor
calls, so replace them with alloc_pgtable_late().

Signed-off-by: Kevin Brodsky <redacted>
---
 arch/riscv/mm/init.c | 63 ++++++++++++----------------------------------------
 1 file changed, 14 insertions(+), 49 deletions(-)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 5b1b3c88b4d1..e823662be256 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c

@@ -382,6 +382,14 @@ void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot)
 	local_flush_tlb_page(addr);
 }
 
+static phys_addr_t __meminit alloc_pgtable_late(uintptr_t va)
+{
+	struct ptdesc *ptdesc = pagetable_alloc(GFP_KERNEL, 0);
+
+	BUG_ON(!ptdesc);
+	return __pa(ptdesc_address(ptdesc));
+}
+
 static inline pte_t *__init get_pte_virt_early(phys_addr_t pa)
 {
 	return (pte_t *)((uintptr_t)pa);

@@ -412,19 +420,6 @@ static inline phys_addr_t __init alloc_pte_fixmap(uintptr_t va)
 	return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
 }
 
-static phys_addr_t __meminit alloc_pte_late(uintptr_t va)
-{
-	struct ptdesc *ptdesc = pagetable_alloc(GFP_KERNEL, 0);
-
-	/*
-	 * We do not know which mm the PTE page is associated to at this point.
-	 * Passing NULL to the ctor is the safe option, though it may result
-	 * in unnecessary work (e.g. initialising the ptlock for init_mm).
-	 */
-	BUG_ON(!ptdesc || !pagetable_pte_ctor(NULL, ptdesc));
-	return __pa((pte_t *)ptdesc_address(ptdesc));
-}
-
 static void __meminit create_pte_mapping(pte_t *ptep, uintptr_t va, phys_addr_t pa, phys_addr_t sz,
 					 pgprot_t prot)
 {

@@ -479,15 +474,6 @@ static phys_addr_t __init alloc_pmd_fixmap(uintptr_t va)
 	return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
 }
 
-static phys_addr_t __meminit alloc_pmd_late(uintptr_t va)
-{
-	struct ptdesc *ptdesc = pagetable_alloc(GFP_KERNEL, 0);
-
-	/* See comment in alloc_pte_late() regarding NULL passed the ctor */
-	BUG_ON(!ptdesc || !pagetable_pmd_ctor(NULL, ptdesc));
-	return __pa((pmd_t *)ptdesc_address(ptdesc));
-}
-
 static void __meminit create_pmd_mapping(pmd_t *pmdp,
 					 uintptr_t va, phys_addr_t pa,
 					 phys_addr_t sz, pgprot_t prot)

@@ -544,15 +530,6 @@ static phys_addr_t __init alloc_pud_fixmap(uintptr_t va)
 	return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
 }
 
-static phys_addr_t __meminit alloc_pud_late(uintptr_t va)
-{
-	struct ptdesc *ptdesc = pagetable_alloc(GFP_KERNEL, 0);
-
-	BUG_ON(!ptdesc);
-	pagetable_pud_ctor(ptdesc);
-	return __pa((pud_t *)ptdesc_address(ptdesc));
-}
-
 static p4d_t *__init get_p4d_virt_early(phys_addr_t pa)
 {
 	return (p4d_t *)((uintptr_t)pa);

@@ -582,15 +559,6 @@ static phys_addr_t __init alloc_p4d_fixmap(uintptr_t va)
 	return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
 }
 
-static phys_addr_t __meminit alloc_p4d_late(uintptr_t va)
-{
-	struct ptdesc *ptdesc = pagetable_alloc(GFP_KERNEL, 0);
-
-	BUG_ON(!ptdesc);
-	pagetable_p4d_ctor(ptdesc);
-	return __pa((p4d_t *)ptdesc_address(ptdesc));
-}
-
 static void __meminit create_pud_mapping(pud_t *pudp, uintptr_t va, phys_addr_t pa, phys_addr_t sz,
 					 pgprot_t prot)
 {

@@ -1003,14 +971,14 @@ static void __init pt_ops_set_fixmap(void)
  */
 static void __init pt_ops_set_late(void)
 {
-	pt_ops.alloc_pte = alloc_pte_late;
+	pt_ops.alloc_pte = alloc_pgtable_late;
 	pt_ops.get_pte_virt = get_pte_virt_late;
 #ifndef __PAGETABLE_PMD_FOLDED
-	pt_ops.alloc_pmd = alloc_pmd_late;
+	pt_ops.alloc_pmd = alloc_pgtable_late;
 	pt_ops.get_pmd_virt = get_pmd_virt_late;
-	pt_ops.alloc_pud = alloc_pud_late;
+	pt_ops.alloc_pud = alloc_pgtable_late;
 	pt_ops.get_pud_virt = get_pud_virt_late;
-	pt_ops.alloc_p4d = alloc_p4d_late;
+	pt_ops.alloc_p4d = alloc_pgtable_late;
 	pt_ops.get_p4d_virt = get_p4d_virt_late;
 #endif
 }

@@ -1488,7 +1456,6 @@ static void __meminit free_pte_table(pte_t *pte_start, pmd_t *pmd)
 			return;
 	}
 
-	pagetable_dtor(ptdesc);
 	if (PageReserved(page))
 		free_reserved_page(page);
 	else

@@ -1496,7 +1463,7 @@ static void __meminit free_pte_table(pte_t *pte_start, pmd_t *pmd)
 	pmd_clear(pmd);
 }
 
-static void __meminit free_pmd_table(pmd_t *pmd_start, pud_t *pud, bool is_vmemmap)
+static void __meminit free_pmd_table(pmd_t *pmd_start, pud_t *pud)
 {
 	struct page *page = pud_page(*pud);
 	struct ptdesc *ptdesc = page_ptdesc(page);

@@ -1509,8 +1476,6 @@ static void __meminit free_pmd_table(pmd_t *pmd_start, pud_t *pud, bool is_vmemm
 			return;
 	}
 
-	if (!is_vmemmap)
-		pagetable_dtor(ptdesc);
 	if (PageReserved(page))
 		free_reserved_page(page);
 	else

@@ -1634,7 +1599,7 @@ static void __meminit remove_pud_mapping(pud_t *pud_base, unsigned long addr, un
 		remove_pmd_mapping(pmd_base, addr, next, is_vmemmap, altmap);
 
 		if (pgtable_l4_enabled)
-			free_pmd_table(pmd_base, pudp, is_vmemmap);
+			free_pmd_table(pmd_base, pudp);
 	}
 }

-- 
2.51.2

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