Re: [PATCH V3 1/6] powerpc/mm/book3s: Update pmd_present to look at _PAGE_PRESENT bit

With this patch we use 0x8000000000000000UL (_PAGE_PRESENT) to indicate a valid
pgd/pud/pmd entry. We also switch the p**_present() to look at this bit.

With pmd_present, we have a special case. We need to make sure we consider a
pmd marked invalid during THP split as present. Right now we clear the
_PAGE_PRESENT bit during a pmdp_invalidate. Inorder to consider this special
case we add a new pte bit _PAGE_INVALID (mapped to _RPAGE_SW0). This bit is
only used with _PAGE_PRESENT cleared. Hence we are not really losing a pte bit
for this special case. pmd_present is also updated to look at _PAGE_INVALID.

Signed-off-by: Aneesh Kumar K.V <redacted>
---
  arch/powerpc/include/asm/book3s/64/hash.h    |  5 +++++
  arch/powerpc/include/asm/book3s/64/pgtable.h | 14 +++++++++++---
  arch/powerpc/mm/hash_utils_64.c              |  6 +++---
  arch/powerpc/mm/pgtable-book3s64.c           |  8 ++++++--
  arch/powerpc/mm/pgtable.c                    |  7 +++----
  5 files changed, 28 insertions(+), 12 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/64/hash.h b/arch/powerpc/include/asm/book3s/64/hash.h
index d52a51b2ce7b..fcf8b10a209f 100644
--- a/arch/powerpc/include/asm/book3s/64/hash.h
+++ b/arch/powerpc/include/asm/book3s/64/hash.h

@@ -18,6 +18,11 @@
  #include <asm/book3s/64/hash-4k.h>
  #endif
  
+/* Bits to set in a PMD/PUD/PGD entry valid bit*/
+#define HASH_PMD_VAL_BITS		(0x8000000000000000UL)
+#define HASH_PUD_VAL_BITS		(0x8000000000000000UL)
+#define HASH_PGD_VAL_BITS		(0x8000000000000000UL)
+
  /*
   * Size of EA range mapped by our pagetables.
   */

diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index 13a688fc8cd0..8feb4a3240d5 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h

@@ -875,8 +875,16 @@ static inline int pmd_none(pmd_t pmd)
  
  static inline int pmd_present(pmd_t pmd)
  {
+	/*
+	 * A pmd is considerent present if _PAGE_PRESENT is set.
+	 * We also need to consider the pmd present which is marked
+	 * invalid during a split. Hence we look for _PAGE_INVALID
+	 * if we find _PAGE_PRESENT cleared.
+	 */
+	if (pmd_raw(pmd) & cpu_to_be64(_PAGE_PRESENT | _PAGE_INVALID))
+		return true;
  
-	return !pmd_none(pmd);
+	return false;
  }
  
  static inline int pmd_bad(pmd_t pmd)

@@ -903,7 +911,7 @@ static inline int pud_none(pud_t pud)
  
  static inline int pud_present(pud_t pud)
  {
-	return !pud_none(pud);
+	return (pud_raw(pud) & cpu_to_be64(_PAGE_PRESENT));
  }
  
  extern struct page *pud_page(pud_t pud);

@@ -950,7 +958,7 @@ static inline int pgd_none(pgd_t pgd)
  
  static inline int pgd_present(pgd_t pgd)
  {
-	return !pgd_none(pgd);
+	return (pgd_raw(pgd) & cpu_to_be64(_PAGE_PRESENT));
  }
  
  static inline pte_t pgd_pte(pgd_t pgd)

diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
index 88c95dc8b141..13ba718c9680 100644
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c

@@ -1001,9 +1001,9 @@ void __init hash__early_init_mmu(void)
  	 * 4k use hugepd format, so for hash set then to
  	 * zero
  	 */
-	__pmd_val_bits = 0;
-	__pud_val_bits = 0;
-	__pgd_val_bits = 0;
+	__pmd_val_bits = HASH_PMD_VAL_BITS;
+	__pud_val_bits = HASH_PUD_VAL_BITS;
+	__pgd_val_bits = HASH_PGD_VAL_BITS;
  
  	__kernel_virt_start = H_KERN_VIRT_START;
  	__kernel_virt_size = H_KERN_VIRT_SIZE;

diff --git a/arch/powerpc/mm/pgtable-book3s64.c b/arch/powerpc/mm/pgtable-book3s64.c
index 01d7c0f7c4f0..654000da8b15 100644
--- a/arch/powerpc/mm/pgtable-book3s64.c
+++ b/arch/powerpc/mm/pgtable-book3s64.c

@@ -69,7 +69,11 @@ void set_pmd_at(struct mm_struct *mm, unsigned long addr,
  		pmd_t *pmdp, pmd_t pmd)
  {
  #ifdef CONFIG_DEBUG_VM
-	WARN_ON(pte_present(pmd_pte(*pmdp)) && !pte_protnone(pmd_pte(*pmdp)));
+	/*
+	 * Make sure hardware valid bit is not set. We don't do
+	 * tlb flush for this update.
+	 */
+	WARN_ON(pte_val(pmd_pte(*pmdp)) & _PAGE_PRESENT);
  	assert_spin_locked(pmd_lockptr(mm, pmdp));
  	WARN_ON(!(pmd_trans_huge(pmd) || pmd_devmap(pmd)));
  #endif

@@ -106,7 +110,7 @@ pmd_t pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
  {
  	unsigned long old_pmd;
  
-	old_pmd = pmd_hugepage_update(vma->vm_mm, address, pmdp, _PAGE_PRESENT, 0);
+	old_pmd = pmd_hugepage_update(vma->vm_mm, address, pmdp, _PAGE_PRESENT, _PAGE_INVALID);
  	flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
  	/*
  	 * This ensures that generic code that rely on IRQ disabling

diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
index d71c7777669c..aee04b209b51 100644
--- a/arch/powerpc/mm/pgtable.c
+++ b/arch/powerpc/mm/pgtable.c

@@ -188,11 +188,10 @@ void set_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep,
  		pte_t pte)
  {
  	/*
-	 * When handling numa faults, we already have the pte marked
-	 * _PAGE_PRESENT, but we can be sure that it is not in hpte.
-	 * Hence we can use set_pte_at for them.
+	 * Make sure hardware valid bit is not set. We don't do
+	 * tlb flush for this update.
  	 */
-	VM_WARN_ON(pte_present(*ptep) && !pte_protnone(*ptep));
+	VM_WARN_ON(pte_val(*ptep) & _PAGE_PRESENT);