parisc: Protect huge page pte changes with spinlocks

PA-RISC doesn't have atomic instructions to modify page table entries, so it
takes spinlock in the TLB handler and modifies the page table entry
non-atomically. If you modify the page table entry without the spinlock, you
may race with TLB handler on another CPU and your modification may be lost.
Protect against that with usage of purge_tlb_start() and purge_tlb_end() which
handles the TLB spinlock.

Signed-off-by: Helge Deller <[e-mail]>
Cc: [e-mail] # v4.4

arch/parisc/include/asm/hugetlb.h

···
 	return pte_wrprotect(pte);
 }
 
-static inline void huge_ptep_set_wrprotect(struct mm_struct *mm,
-					   unsigned long addr, pte_t *ptep)
-{
-	pte_t old_pte = *ptep;
-	set_huge_pte_at(mm, addr, ptep, pte_wrprotect(old_pte));
-}
+void huge_ptep_set_wrprotect(struct mm_struct *mm,
+					   unsigned long addr, pte_t *ptep);
 
-static inline int huge_ptep_set_access_flags(struct vm_area_struct *vma,
+int huge_ptep_set_access_flags(struct vm_area_struct *vma,
 					     unsigned long addr, pte_t *ptep,
-					     pte_t pte, int dirty)
-{
-	int changed = !pte_same(*ptep, pte);
-	if (changed) {
-		set_huge_pte_at(vma->vm_mm, addr, ptep, pte);
-		flush_tlb_page(vma, addr);
-	}
-	return changed;
-}
+					     pte_t pte, int dirty);
 
 static inline pte_t huge_ptep_get(pte_t *ptep)
 {

arch/parisc/mm/hugetlbpage.c

···
 	addr |= _HUGE_PAGE_SIZE_ENCODING_DEFAULT;
 
 	for (i = 0; i < (1 << (HPAGE_SHIFT-REAL_HPAGE_SHIFT)); i++) {
-		mtsp(mm->context, 1);
-		pdtlb(addr);
-		if (unlikely(split_tlb))
-			pitlb(addr);
+		purge_tlb_entries(mm, addr);
 		addr += (1UL << REAL_HPAGE_SHIFT);
 	}
 }
 
-void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
+/* __set_huge_pte_at() must be called holding the pa_tlb_lock. */
+static void __set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
 		     pte_t *ptep, pte_t entry)
 {
 	unsigned long addr_start;
···
 	addr_start = addr;
 
 	for (i = 0; i < (1 << HUGETLB_PAGE_ORDER); i++) {
-		/* Directly write pte entry.  We could call set_pte_at(mm, addr, ptep, entry)
-		 * instead, but then we get double locking on pa_tlb_lock. */
-		*ptep = entry;
+		set_pte(ptep, entry);
 		ptep++;
-
-		/* Drop the PAGE_SIZE/non-huge tlb entry */
-		purge_tlb_entries(mm, addr);
 
 		addr += PAGE_SIZE;
 		pte_val(entry) += PAGE_SIZE;
···
 	purge_tlb_entries_huge(mm, addr_start);
 }
 
+void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
+		     pte_t *ptep, pte_t entry)
+{
+	unsigned long flags;
+
+	purge_tlb_start(flags);
+	__set_huge_pte_at(mm, addr, ptep, entry);
+	purge_tlb_end(flags);
+}
+
 
 pte_t huge_ptep_get_and_clear(struct mm_struct *mm, unsigned long addr,
 			      pte_t *ptep)
 {
+	unsigned long flags;
 	pte_t entry;
 
+	purge_tlb_start(flags);
 	entry = *ptep;
-	set_huge_pte_at(mm, addr, ptep, __pte(0));
+	__set_huge_pte_at(mm, addr, ptep, __pte(0));
+	purge_tlb_end(flags);
 
 	return entry;
 }
+
+
+void huge_ptep_set_wrprotect(struct mm_struct *mm,
+				unsigned long addr, pte_t *ptep)
+{
+	unsigned long flags;
+	pte_t old_pte;
+
+	purge_tlb_start(flags);
+	old_pte = *ptep;
+	__set_huge_pte_at(mm, addr, ptep, pte_wrprotect(old_pte));
+	purge_tlb_end(flags);
+}
+
+int huge_ptep_set_access_flags(struct vm_area_struct *vma,
+				unsigned long addr, pte_t *ptep,
+				pte_t pte, int dirty)
+{
+	unsigned long flags;
+	int changed;
+
+	purge_tlb_start(flags);
+	changed = !pte_same(*ptep, pte);
+	if (changed) {
+		__set_huge_pte_at(vma->vm_mm, addr, ptep, pte);
+	}
+	purge_tlb_end(flags);
+	return changed;
+}
+
 
 int pmd_huge(pmd_t pmd)
 {