[PATCHv6 15/16] x86/mm: Introduce kernel_ident_mapping_free()

[Kirill A. Shutemov]

The helper complements kernel_ident_mapping_init(): it frees the
identity mapping that was previously allocated. It will be used in the
error path to free a partially allocated mapping or if the mapping is no
longer needed.

The caller provides a struct x86_mapping_info with the free_pgd_page()
callback hooked up and the pgd_t to free.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/init.h |  3 ++
 arch/x86/mm/ident_map.c     | 73 +++++++++++++++++++++++++++++++++++++
 2 files changed, 76 insertions(+)

diff --git a/arch/x86/include/asm/init.h b/arch/x86/include/asm/init.h
index cc9ccf61b6bd..14d72727d7ee 100644
--- a/arch/x86/include/asm/init.h
+++ b/arch/x86/include/asm/init.h
@@ -6,6 +6,7 @@
 
 struct x86_mapping_info {
 	void *(*alloc_pgt_page)(void *); /* allocate buf for page table */
+	void (*free_pgt_page)(void *, void *); /* free buf for page table */
 	void *context;			 /* context for alloc_pgt_page */
 	unsigned long page_flag;	 /* page flag for PMD or PUD entry */
 	unsigned long offset;		 /* ident mapping offset */
@@ -16,4 +17,6 @@ struct x86_mapping_info {
 int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t *pgd_page,
 				unsigned long pstart, unsigned long pend);
 
+void kernel_ident_mapping_free(struct x86_mapping_info *info, pgd_t *pgd);
+
 #endif /* _ASM_X86_INIT_H */
diff --git a/arch/x86/mm/ident_map.c b/arch/x86/mm/ident_map.c
index 968d7005f4a7..3996af7b4abf 100644
--- a/arch/x86/mm/ident_map.c
+++ b/arch/x86/mm/ident_map.c
@@ -4,6 +4,79 @@
  * included by both the compressed kernel and the regular kernel.
  */
 
+static void free_pte(struct x86_mapping_info *info, pmd_t *pmd)
+{
+	pte_t *pte = pte_offset_kernel(pmd, 0);
+
+	info->free_pgt_page(pte, info->context);
+}
+
+static void free_pmd(struct x86_mapping_info *info, pud_t *pud)
+{
+	pmd_t *pmd = pmd_offset(pud, 0);
+	int i;
+
+	for (i = 0; i < PTRS_PER_PMD; i++) {
+		if (!pmd_present(pmd[i]))
+			continue;
+
+		if (pmd_leaf(pmd[i]))
+			continue;
+
+		free_pte(info, &pmd[i]);
+	}
+
+	info->free_pgt_page(pmd, info->context);
+}
+
+static void free_pud(struct x86_mapping_info *info, p4d_t *p4d)
+{
+	pud_t *pud = pud_offset(p4d, 0);
+	int i;
+
+	for (i = 0; i < PTRS_PER_PUD; i++) {
+		if (!pud_present(pud[i]))
+			continue;
+
+		if (pud_leaf(pud[i]))
+			continue;
+
+		free_pmd(info, &pud[i]);
+	}
+
+	info->free_pgt_page(pud, info->context);
+}
+
+static void free_p4d(struct x86_mapping_info *info, pgd_t *pgd)
+{
+	p4d_t *p4d = p4d_offset(pgd, 0);
+	int i;
+
+	for (i = 0; i < PTRS_PER_P4D; i++) {
+		if (!p4d_present(p4d[i]))
+			continue;
+
+		free_pud(info, &p4d[i]);
+	}
+
+	if (pgtable_l5_enabled())
+		info->free_pgt_page(pgd, info->context);
+}
+
+void kernel_ident_mapping_free(struct x86_mapping_info *info, pgd_t *pgd)
+{
+	int i;
+
+	for (i = 0; i < PTRS_PER_PGD; i++) {
+		if (!pgd_present(pgd[i]))
+			continue;
+
+		free_p4d(info, &pgd[i]);
+	}
+
+	info->free_pgt_page(pgd, info->context);
+}
+
 static void ident_pmd_init(struct x86_mapping_info *info, pmd_t *pmd_page,
 			   unsigned long addr, unsigned long end)
 {
-- 
2.43.0