x86/acpi: Replace manual page table initialization with kernel_ident_mapping_init()

The init_transition_pgtable() functions maps the page with
asm_acpi_mp_play_dead() into an identity mapping.

Replace open-coded manual page table initialization with
kernel_ident_mapping_init() to avoid code duplication.

Use x86_mapping_info::offset to get the page mapped at the
correct location.

Signed-off-by: Kirill A. Shutemov <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>
Reviewed-by: Kai Huang <[e-mail]>
Reviewed-by: Tom Lendacky <[e-mail]>
Acked-by: Rafael J. Wysocki <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/x86/kernel/acpi/madt_wakeup.c

···
 	return memblock_free(pgt, PAGE_SIZE);
 }
 
-/*
- * Make sure asm_acpi_mp_play_dead() is present in the identity mapping at
- * the same place as in the kernel page tables. asm_acpi_mp_play_dead() switches
- * to the identity mapping and the function has be present at the same spot in
- * the virtual address space before and after switching page tables.
- */
-static int __init init_transition_pgtable(pgd_t *pgd)
-{
-	pgprot_t prot = PAGE_KERNEL_EXEC_NOENC;
-	unsigned long vaddr, paddr;
-	p4d_t *p4d;
-	pud_t *pud;
-	pmd_t *pmd;
-	pte_t *pte;
-
-	vaddr = (unsigned long)asm_acpi_mp_play_dead;
-	pgd += pgd_index(vaddr);
-	if (!pgd_present(*pgd)) {
-		p4d = (p4d_t *)alloc_pgt_page(NULL);
-		if (!p4d)
-			return -ENOMEM;
-		set_pgd(pgd, __pgd(__pa(p4d) | _KERNPG_TABLE));
-	}
-	p4d = p4d_offset(pgd, vaddr);
-	if (!p4d_present(*p4d)) {
-		pud = (pud_t *)alloc_pgt_page(NULL);
-		if (!pud)
-			return -ENOMEM;
-		set_p4d(p4d, __p4d(__pa(pud) | _KERNPG_TABLE));
-	}
-	pud = pud_offset(p4d, vaddr);
-	if (!pud_present(*pud)) {
-		pmd = (pmd_t *)alloc_pgt_page(NULL);
-		if (!pmd)
-			return -ENOMEM;
-		set_pud(pud, __pud(__pa(pmd) | _KERNPG_TABLE));
-	}
-	pmd = pmd_offset(pud, vaddr);
-	if (!pmd_present(*pmd)) {
-		pte = (pte_t *)alloc_pgt_page(NULL);
-		if (!pte)
-			return -ENOMEM;
-		set_pmd(pmd, __pmd(__pa(pte) | _KERNPG_TABLE));
-	}
-	pte = pte_offset_kernel(pmd, vaddr);
-
-	paddr = __pa(vaddr);
-	set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, prot));
-
-	return 0;
-}
-
 static int __init acpi_mp_setup_reset(u64 reset_vector)
 {
 	struct x86_mapping_info info = {
···
 		.page_flag      = __PAGE_KERNEL_LARGE_EXEC,
 		.kernpg_flag    = _KERNPG_TABLE_NOENC,
 	};
+	unsigned long mstart, mend;
 	pgd_t *pgd;
 
 	pgd = alloc_pgt_page(NULL);
···
 		return -ENOMEM;
 
 	for (int i = 0; i < nr_pfn_mapped; i++) {
-		unsigned long mstart, mend;
-
 		mstart = pfn_mapped[i].start << PAGE_SHIFT;
 		mend   = pfn_mapped[i].end << PAGE_SHIFT;
 		if (kernel_ident_mapping_init(&info, pgd, mstart, mend)) {
···
 		}
 	}
 
-	if (kernel_ident_mapping_init(&info, pgd,
-				      PAGE_ALIGN_DOWN(reset_vector),
-				      PAGE_ALIGN(reset_vector + 1))) {
+	mstart = PAGE_ALIGN_DOWN(reset_vector);
+	mend = mstart + PAGE_SIZE;
+	if (kernel_ident_mapping_init(&info, pgd, mstart, mend)) {
 		kernel_ident_mapping_free(&info, pgd);
 		return -ENOMEM;
 	}
 
-	if (init_transition_pgtable(pgd)) {
+	/*
+	 * Make sure asm_acpi_mp_play_dead() is present in the identity mapping
+	 * at the same place as in the kernel page tables.
+	 * asm_acpi_mp_play_dead() switches to the identity mapping and the
+	 * function must be present at the same spot in the virtual address space
+	 * before and after switching page tables.
+	 */
+	info.offset = __START_KERNEL_map - phys_base;
+	mstart = PAGE_ALIGN_DOWN(__pa(asm_acpi_mp_play_dead));
+	mend = mstart + PAGE_SIZE;
+	if (kernel_ident_mapping_init(&info, pgd, mstart, mend)) {
 		kernel_ident_mapping_free(&info, pgd);
 		return -ENOMEM;
 	}