[PATCHv1, RFC 5/8] x86/mm: Fold p4d page table layer at runtime

[Kirill A. Shutemov]

This patch changes page table helpers to fold p4d at runtime.
The logic is the same as in <asm-generic/pgtable-nop4d.h>.

Signed-off-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com>
---
 arch/x86/include/asm/paravirt.h |  3 ++-
 arch/x86/include/asm/pgalloc.h  |  5 ++++-
 arch/x86/include/asm/pgtable.h  | 10 +++++++++-
 3 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 55fa56fe4e45..e934ed6dc036 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -615,7 +615,8 @@ static inline void set_pgd(pgd_t *pgdp, pgd_t pgd)
 
 static inline void pgd_clear(pgd_t *pgdp)
 {
-       set_pgd(pgdp, __pgd(0));
+       if (!p4d_folded)
+               set_pgd(pgdp, __pgd(0));
 }
 
 #endif  /* CONFIG_PGTABLE_LEVELS == 5 */
diff --git a/arch/x86/include/asm/pgalloc.h b/arch/x86/include/asm/pgalloc.h
index b2d0cd8288aa..5c42262169d0 100644
--- a/arch/x86/include/asm/pgalloc.h
+++ b/arch/x86/include/asm/pgalloc.h
@@ -155,6 +155,8 @@ static inline void __pud_free_tlb(struct mmu_gather *tlb, 
pud_t *pud,
 #if CONFIG_PGTABLE_LEVELS > 4
 static inline void pgd_populate(struct mm_struct *mm, pgd_t *pgd, p4d_t *p4d)
 {
+       if (p4d_folded)
+               return;
        paravirt_alloc_p4d(mm, __pa(p4d) >> PAGE_SHIFT);
        set_pgd(pgd, __pgd(_PAGE_TABLE | __pa(p4d)));
 }
@@ -179,7 +181,8 @@ extern void ___p4d_free_tlb(struct mmu_gather *tlb, p4d_t 
*p4d);
 static inline void __p4d_free_tlb(struct mmu_gather *tlb, p4d_t *p4d,
                                  unsigned long address)
 {
-       ___p4d_free_tlb(tlb, p4d);
+       if (!p4d_folded)
+               ___p4d_free_tlb(tlb, p4d);
 }
 
 #endif /* CONFIG_PGTABLE_LEVELS > 4 */
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 77037b6f1caa..4516a1bdcc31 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -53,7 +53,7 @@ extern struct mm_struct *pgd_page_get_mm(struct page *page);
 
 #ifndef __PAGETABLE_P4D_FOLDED
 #define set_pgd(pgdp, pgd)             native_set_pgd(pgdp, pgd)
-#define pgd_clear(pgd)                 native_pgd_clear(pgd)
+#define pgd_clear(pgd)                 (!p4d_folded ? native_pgd_clear(pgd) : 
0)
 #endif
 
 #ifndef set_p4d
@@ -847,6 +847,8 @@ static inline unsigned long p4d_index(unsigned long address)
 #if CONFIG_PGTABLE_LEVELS > 4
 static inline int pgd_present(pgd_t pgd)
 {
+       if (p4d_folded)
+               return 1;
        return pgd_flags(pgd) & _PAGE_PRESENT;
 }
 
@@ -864,16 +866,22 @@ static inline unsigned long pgd_page_vaddr(pgd_t pgd)
 /* to find an entry in a page-table-directory. */
 static inline p4d_t *p4d_offset(pgd_t *pgd, unsigned long address)
 {
+       if (p4d_folded)
+               return (p4d_t *)pgd;
        return (p4d_t *)pgd_page_vaddr(*pgd) + p4d_index(address);
 }
 
 static inline int pgd_bad(pgd_t pgd)
 {
+       if (p4d_folded)
+               return 0;
        return (pgd_flags(pgd) & ~_PAGE_USER) != _KERNPG_TABLE;
 }
 
 static inline int pgd_none(pgd_t pgd)
 {
+       if (p4d_folded)
+               return 0;
        /*
         * There is no need to do a workaround for the KNL stray
         * A/D bit erratum here.  PGDs only point to page tables
-- 
2.11.0