[PATCH v2] MIPS: fix pmd_mkinvalid

[Hongchen Zhang]

  There is a problem now:
	    CPU 0		CPU 1
	pmdp_invalidate		do_page_fault
	...			  __handle_mm_fault
				    is_swap_pmd == true
				    trigger VM_BUG_ON() ?
	set_pmd_at
  the reason is when a pmd entry is invalidated by pmd_mkinvalid,
  pmd_present should return true but now pmd_present return false.

  Like arm64 does in
  commit b65399f6111b ("arm64/mm: Change THP helpers to comply with
  generic MM semantics"). we introduce a _PMD_PRESENT_INVALID_SHIFT
  bit to check if a pmd is present but invalidated by pmd_mkinvalid.

  After this commit pmd_present will return the correct value and
  the VM_BUG_ON will not be triggered.

Signed-off-by: Hongchen Zhang <zhanghongchen@xxxxxxxxxxx>
---
 arch/mips/include/asm/pgtable-64.h   | 2 +-
 arch/mips/include/asm/pgtable-bits.h | 2 ++
 arch/mips/include/asm/pgtable.h      | 3 +++
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/mips/include/asm/pgtable-64.h b/arch/mips/include/asm/pgtable-64.h
index 41921ac..050cf66 100644
--- a/arch/mips/include/asm/pgtable-64.h
+++ b/arch/mips/include/asm/pgtable-64.h
@@ -265,7 +265,7 @@ static inline int pmd_present(pmd_t pmd)
 {
 #ifdef CONFIG_MIPS_HUGE_TLB_SUPPORT
 	if (unlikely(pmd_val(pmd) & _PAGE_HUGE))
-		return pmd_val(pmd) & _PAGE_PRESENT;
+		return pmd_val(pmd) & (_PAGE_PRESENT | _PMD_PRESENT_INVALID);
 #endif
 
 	return pmd_val(pmd) != (unsigned long) invalid_pte_table;
diff --git a/arch/mips/include/asm/pgtable-bits.h b/arch/mips/include/asm/pgtable-bits.h
index 2362842..72cd88a 100644
--- a/arch/mips/include/asm/pgtable-bits.h
+++ b/arch/mips/include/asm/pgtable-bits.h
@@ -130,6 +130,7 @@ enum pgtable_bits {
 	_PAGE_MODIFIED_SHIFT,
 #if defined(CONFIG_MIPS_HUGE_TLB_SUPPORT)
 	_PAGE_HUGE_SHIFT,
+	_PMD_PRESENT_INVALID_SHIFT,
 #endif
 #if defined(CONFIG_ARCH_HAS_PTE_SPECIAL)
 	_PAGE_SPECIAL_SHIFT,
@@ -157,6 +158,7 @@ enum pgtable_bits {
 #define _PAGE_MODIFIED		(1 << _PAGE_MODIFIED_SHIFT)
 #if defined(CONFIG_MIPS_HUGE_TLB_SUPPORT)
 # define _PAGE_HUGE		(1 << _PAGE_HUGE_SHIFT)
+#define _PMD_PRESENT_INVALID	(1 << _PMD_PRESENT_INVALID_SHIFT)
 #endif
 #if defined(CONFIG_ARCH_HAS_PTE_SPECIAL)
 # define _PAGE_SPECIAL		(1 << _PAGE_SPECIAL_SHIFT)
diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h
index 374c632..a75f461 100644
--- a/arch/mips/include/asm/pgtable.h
+++ b/arch/mips/include/asm/pgtable.h
@@ -696,12 +696,15 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
 	return pmd;
 }
 
+#ifdef CONFIG_MIPS_HUGE_TLB_SUPPORT
 static inline pmd_t pmd_mkinvalid(pmd_t pmd)
 {
+	pmd_val(pmd) |= _PMD_PRESENT_INVALID;
 	pmd_val(pmd) &= ~(_PAGE_PRESENT | _PAGE_VALID | _PAGE_DIRTY);
 
 	return pmd;
 }
+#endif
 
 /*
  * The generic version pmdp_huge_get_and_clear uses a version of pmd_clear() with a
-- 
1.8.3.1