[RFC, PATCHv1 10/28] x86/mm: add support of p4d_t in vmalloc_fault()

[Kirill A. Shutemov]

With 4-level paging copying happens on p4d level, as we have pgd_none()
always false when p4d_t folded.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 arch/x86/mm/fault.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 1bbdbb0594a3..820e8c284796 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -434,6 +434,7 @@ void vmalloc_sync_all(void)
 static noinline int vmalloc_fault(unsigned long address)
 {
 	pgd_t *pgd, *pgd_ref;
+	p4d_t *p4d, *p4d_ref;
 	pud_t *pud, *pud_ref;
 	pmd_t *pmd, *pmd_ref;
 	pte_t *pte, *pte_ref;
@@ -461,13 +462,26 @@ static noinline int vmalloc_fault(unsigned long address)
 		BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref));
 	}
 
+	/* With 4-level paging copying happens on p4d level. */
+	p4d = p4d_offset(pgd, address);
+	p4d_ref = p4d_offset(pgd_ref, address);
+	if (p4d_none(*p4d_ref))
+		return -1;
+
+	if (p4d_none(*p4d)) {
+		set_p4d(p4d, *p4d_ref);
+		arch_flush_lazy_mmu_mode();
+	} else {
+		BUG_ON(p4d_pfn(*p4d) != p4d_pfn(*p4d_ref));
+	}
+
 	/*
 	 * Below here mismatches are bugs because these lower tables
 	 * are shared:
 	 */
 
-	pud = pud_offset(pgd, address);
-	pud_ref = pud_offset(pgd_ref, address);
+	pud = pud_offset(p4d, address);
+	pud_ref = pud_offset(p4d_ref, address);
 	if (pud_none(*pud_ref))
 		return -1;
 
-- 
2.10.2