[PATCH 4/6] x86/ident_map: Add 5-level paging support

["Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>]

Add additional page table level handing. It's mostly mechanical.

The only quirk is that with p4d folded, 'pgd' is equal to 'p4d' in
kernel_ident_mapping_init(). pgd entry has to point pud page table in
this case.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 arch/x86/mm/ident_map.c | 51 ++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 44 insertions(+), 7 deletions(-)

diff --git a/arch/x86/mm/ident_map.c b/arch/x86/mm/ident_map.c
index 4473cb4f8b90..1c3f166bd8c3 100644
--- a/arch/x86/mm/ident_map.c
+++ b/arch/x86/mm/ident_map.c
@@ -45,6 +45,34 @@ static int ident_pud_init(struct x86_mapping_info *info, pud_t *pud_page,
 	return 0;
 }
 
+static int ident_p4d_init(struct x86_mapping_info *info, p4d_t *p4d_page,
+			  unsigned long addr, unsigned long end)
+{
+	unsigned long next;
+
+	for (; addr < end; addr = next) {
+		p4d_t *p4d = p4d_page + p4d_index(addr);
+		pud_t *pud;
+
+		next = (addr & P4D_MASK) + P4D_SIZE;
+		if (next > end)
+			next = end;
+
+		if (p4d_present(*p4d)) {
+			pud = pud_offset(p4d, 0);
+			ident_pud_init(info, pud, addr, next);
+			continue;
+		}
+		pud = (pud_t *)info->alloc_pgt_page(info->context);
+		if (!pud)
+			return -ENOMEM;
+		ident_pud_init(info, pud, addr, next);
+		set_p4d(p4d, __p4d(__pa(pud) | _KERNPG_TABLE));
+	}
+
+	return 0;
+}
+
 int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t *pgd_page,
 			      unsigned long pstart, unsigned long pend)
 {
@@ -55,27 +83,36 @@ int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t *pgd_page,
 
 	for (; addr < end; addr = next) {
 		pgd_t *pgd = pgd_page + pgd_index(addr);
-		pud_t *pud;
+		p4d_t *p4d;
 
 		next = (addr & PGDIR_MASK) + PGDIR_SIZE;
 		if (next > end)
 			next = end;
 
 		if (pgd_present(*pgd)) {
-			pud = pud_offset(pgd, 0);
-			result = ident_pud_init(info, pud, addr, next);
+			p4d = p4d_offset(pgd, 0);
+			result = ident_p4d_init(info, p4d, addr, next);
 			if (result)
 				return result;
 			continue;
 		}
 
-		pud = (pud_t *)info->alloc_pgt_page(info->context);
-		if (!pud)
+		p4d = (p4d_t *)info->alloc_pgt_page(info->context);
+		if (!p4d)
 			return -ENOMEM;
-		result = ident_pud_init(info, pud, addr, next);
+		result = ident_p4d_init(info, p4d, addr, next);
 		if (result)
 			return result;
-		set_pgd(pgd, __pgd(__pa(pud) | _KERNPG_TABLE));
+		if (IS_ENABLED(CONFIG_X86_5LEVEL)) {
+			set_pgd(pgd, __pgd(__pa(p4d) | _KERNPG_TABLE));
+		} else {
+			/*
+			 * With p4d folded, pgd is equal to p4d.
+			 * pgd entry has to point pud page table in this case.
+			 */
+			pud_t *pud = pud_offset(p4d, 0);
+			set_pgd(pgd, __pgd(__pa(pud) | _KERNPG_TABLE));
+		}
 	}
 
 	return 0;
-- 
2.11.0

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