[PATCH 05/26] 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.shute...@linux.intel.com>
---
 arch/x86/mm/fault.c | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 605fd5e8e048..88040bb2b78a 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -435,6 +435,7 @@ 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;
@@ -458,17 +459,37 @@ static noinline int vmalloc_fault(unsigned long address)
        if (pgd_none(*pgd)) {
                set_pgd(pgd, *pgd_ref);
                arch_flush_lazy_mmu_mode();
-       } else {
+       } else if (CONFIG_PGTABLE_LEVELS > 4) {
+               /*
+                * With folded p4d, pgd_none() is always false. So pgd may
+                * point to empty page table entry and pgd_page_vaddr()
+                * will return garbage.
+                *
+                * We will do the correct sanity check on p4d level.
+                */
                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;
 
-- 
2.11.0