powerpc/hash64: Restrict page table lookup using init_mm with __flush_hash_table_range

This is only used with init_mm currently. Walking init_mm is much simpler
because we don't need to handle concurrent page table like other mm_context
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200505071729.54912-5-aneesh.kumar@linux.ibm.com

arch/powerpc/include/asm/book3s/64/tlbflush-hash.h

@@ -113,8 +113,7 @@ static inline void hash__flush_tlb_kernel_range(unsigned long start,
 struct mmu_gather;
 extern void hash__tlb_flush(struct mmu_gather *tlb);
 /* Private function for use by PCI IO mapping code */
-extern void __flush_hash_table_range(struct mm_struct *mm, unsigned long start,
-				     unsigned long end);
+extern void __flush_hash_table_range(unsigned long start, unsigned long end);
 extern void flush_tlb_pmd_range(struct mm_struct *mm, pmd_t *pmd,
 				unsigned long addr);
 #endif /*  _ASM_POWERPC_BOOK3S_64_TLBFLUSH_HASH_H */

arch/powerpc/kernel/pci_64.c

@@ -100,7 +100,7 @@ int pcibios_unmap_io_space(struct pci_bus *bus)
 			 pci_name(bus->self));
 
 #ifdef CONFIG_PPC_BOOK3S_64
-		__flush_hash_table_range(&init_mm, res->start + _IO_BASE,
+		__flush_hash_table_range(res->start + _IO_BASE,
 					 res->end + _IO_BASE + 1);
 #endif
 		return 0;

arch/powerpc/mm/book3s64/hash_tlb.c

@@ -176,7 +176,6 @@ void hash__tlb_flush(struct mmu_gather *tlb)
  *                            from the hash table (and the TLB). But keeps
  *                            the linux PTEs intact.
  *
- * @mm		: mm_struct of the target address space (generally init_mm)
  * @start	: starting address
  * @end         : ending address (not included in the flush)
  *
@@ -189,17 +188,14 @@ void hash__tlb_flush(struct mmu_gather *tlb)
  * Because of that usage pattern, it is implemented for small size rather
  * than speed.
  */
-void __flush_hash_table_range(struct mm_struct *mm, unsigned long start,
-			      unsigned long end)
+void __flush_hash_table_range(unsigned long start, unsigned long end)
 {
-	bool is_thp;
 	int hugepage_shift;
 	unsigned long flags;
 
 	start = _ALIGN_DOWN(start, PAGE_SIZE);
 	end = _ALIGN_UP(end, PAGE_SIZE);
 
-	BUG_ON(!mm->pgd);
 
 	/*
 	 * Note: Normally, we should only ever use a batch within a
@@ -212,21 +208,15 @@ void __flush_hash_table_range(struct mm_struct *mm, unsigned long start,
 	local_irq_save(flags);
 	arch_enter_lazy_mmu_mode();
 	for (; start < end; start += PAGE_SIZE) {
-		pte_t *ptep = find_current_mm_pte(mm->pgd, start, &is_thp,
-						  &hugepage_shift);
+		pte_t *ptep = find_init_mm_pte(start, &hugepage_shift);
 		unsigned long pte;
 
 		if (ptep == NULL)
 			continue;
 		pte = pte_val(*ptep);
-		if (is_thp)
-			trace_hugepage_invalidate(start, pte);
 		if (!(pte & H_PAGE_HASHPTE))
 			continue;
-		if (unlikely(is_thp))
-			hpte_do_hugepage_flush(mm, start, (pmd_t *)ptep, pte);
-		else
-			hpte_need_flush(mm, start, ptep, pte, hugepage_shift);
+		hpte_need_flush(&init_mm, start, ptep, pte, hugepage_shift);
 	}
 	arch_leave_lazy_mmu_mode();
 	local_irq_restore(flags);