[PATCH 2/4] riscv/mm: fix hotplug page-table destructor handling

[Muchun Song]

RISC-V uses the same memory-hotplug teardown code for the linear map and
vmemmap, although their page-table pages are not always allocated in the
same way. Late linear-map allocations run page-table constructors, while
vmemmap and early allocations may provide constructor-free pages.

The PTE path unconditionally runs the destructor, which is wrong for
constructor-free vmemmap tables. The PMD path avoids that problem by
using is_vmemmap as a proxy for constructor state, but that assumption
will no longer hold once runtime vmemmap allocations use the normal
pgalloc helpers.

Page-table constructors record their state in PG_table. Centralize
page-table freeing and use PageTable() to decide whether the destructor
is required. Keep reserved and constructor-free pages on their existing
freeing paths.

Fixes: c75a74f4ba19 ("riscv: mm: Add memory hotplugging support")
Cc: stable at vger.kernel.org
Assisted-by: LLM
Signed-off-by: Muchun Song <songmuchun at bytedance.com>
---
 arch/riscv/mm/init.c | 29 ++++++++++++++---------------
 1 file changed, 14 insertions(+), 15 deletions(-)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 857f9a55039c..429a0b015ec1 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -1486,10 +1486,19 @@ struct execmem_info __init *execmem_arch_setup(void)
 #endif /* CONFIG_EXECMEM */
 
 #ifdef CONFIG_MEMORY_HOTPLUG
+static void __meminit free_pagetable(struct page *page)
+{
+	if (PageReserved(page))
+		free_reserved_page(page);
+	else if (PageTable(page))
+		pagetable_dtor_free(page_ptdesc(page));
+	else
+		pagetable_free(page_ptdesc(page));
+}
+
 static void __meminit free_pte_table(pte_t *pte_start, pmd_t *pmd)
 {
 	struct page *page = pmd_page(*pmd);
-	struct ptdesc *ptdesc = page_ptdesc(page);
 	pte_t *pte;
 	int i;
 
@@ -1499,18 +1508,13 @@ 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
-		pagetable_free(ptdesc);
+	free_pagetable(page);
 	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);
 	pmd_t *pmd;
 	int i;
 
@@ -1520,12 +1524,7 @@ 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
-		pagetable_free(ptdesc);
+	free_pagetable(page);
 	pud_clear(pud);
 }
 
@@ -1645,7 +1644,7 @@ 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);
 	}
 }
 
-- 
2.54.0