powerpc/mm/book3s64/iommu: fix some RCU-list locks

It is safe to traverse mm->context.iommu_group_mem_list with either
mem_list_mutex or the RCU read lock held. Silence a few RCU-list false
positive warnings and fix a few missing RCU read locks.

 arch/powerpc/mm/book3s64/iommu_api.c:330 RCU-list traversed in non-reader section!!

 other info that might help us debug this:

 rcu_scheduler_active = 2, debug_locks = 1
 2 locks held by qemu-kvm/4305:
  #0: c000000bc3fe4d68 (&container->lock){+.+.}-{3:3}, at: tce_iommu_ioctl.part.9+0xc7c/0x1870 [vfio_iommu_spapr_tce]
  #1: c000000001501910 (mem_list_mutex){+.+.}-{3:3}, at: mm_iommu_get+0x50/0x190

 ====
 arch/powerpc/mm/book3s64/iommu_api.c:132 RCU-list traversed in non-reader section!!

 other info that might help us debug this:

 rcu_scheduler_active = 2, debug_locks = 1
 2 locks held by qemu-kvm/4305:
  #0: c000000bc3fe4d68 (&container->lock){+.+.}-{3:3}, at: tce_iommu_ioctl.part.9+0xc7c/0x1870 [vfio_iommu_spapr_tce]
  #1: c000000001501910 (mem_list_mutex){+.+.}-{3:3}, at: mm_iommu_do_alloc+0x120/0x5f0

 ====
 arch/powerpc/mm/book3s64/iommu_api.c:292 RCU-list traversed in non-reader section!!

 other info that might help us debug this:

 rcu_scheduler_active = 2, debug_locks = 1
 2 locks held by qemu-kvm/4312:
  #0: c000000ecafe23c8 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0xdc/0x950 [kvm]
  #1: c000000045e6c468 (&kvm->srcu){....}-{0:0}, at: kvmppc_h_put_tce+0x88/0x340 [kvm]

 ====
 arch/powerpc/mm/book3s64/iommu_api.c:424 RCU-list traversed in non-reader section!!

 other info that might help us debug this:

 rcu_scheduler_active = 2, debug_locks = 1
 2 locks held by qemu-kvm/4312:
  #0: c000000ecafe23c8 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0xdc/0x950 [kvm]
  #1: c000000045e6c468 (&kvm->srcu){....}-{0:0}, at: kvmppc_h_put_tce+0x88/0x340 [kvm]
Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200510051559.1959-1-cai@lca.pw

arch/powerpc/mm/book3s64/iommu_api.c

@@ -129,7 +129,8 @@ static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua,
 
 	mutex_lock(&mem_list_mutex);
 
-	list_for_each_entry_rcu(mem2, &mm->context.iommu_group_mem_list, next) {
+	list_for_each_entry_rcu(mem2, &mm->context.iommu_group_mem_list, next,
+				lockdep_is_held(&mem_list_mutex)) {
 		/* Overlap? */
 		if ((mem2->ua < (ua + (entries << PAGE_SHIFT))) &&
 				(ua < (mem2->ua +
@@ -289,6 +290,7 @@ struct mm_iommu_table_group_mem_t *mm_iommu_lookup(struct mm_struct *mm,
 {
 	struct mm_iommu_table_group_mem_t *mem, *ret = NULL;
 
+	rcu_read_lock();
 	list_for_each_entry_rcu(mem, &mm->context.iommu_group_mem_list, next) {
 		if ((mem->ua <= ua) &&
 				(ua + size <= mem->ua +
@@ -297,6 +299,7 @@ struct mm_iommu_table_group_mem_t *mm_iommu_lookup(struct mm_struct *mm,
 			break;
 		}
 	}
+	rcu_read_unlock();
 
 	return ret;
 }
@@ -327,7 +330,8 @@ struct mm_iommu_table_group_mem_t *mm_iommu_get(struct mm_struct *mm,
 
 	mutex_lock(&mem_list_mutex);
 
-	list_for_each_entry_rcu(mem, &mm->context.iommu_group_mem_list, next) {
+	list_for_each_entry_rcu(mem, &mm->context.iommu_group_mem_list, next,
+				lockdep_is_held(&mem_list_mutex)) {
 		if ((mem->ua == ua) && (mem->entries == entries)) {
 			ret = mem;
 			++mem->used;
@@ -421,6 +425,7 @@ bool mm_iommu_is_devmem(struct mm_struct *mm, unsigned long hpa,
 	struct mm_iommu_table_group_mem_t *mem;
 	unsigned long end;
 
+	rcu_read_lock();
 	list_for_each_entry_rcu(mem, &mm->context.iommu_group_mem_list, next) {
 		if (mem->dev_hpa == MM_IOMMU_TABLE_INVALID_HPA)
 			continue;
@@ -437,6 +442,7 @@ bool mm_iommu_is_devmem(struct mm_struct *mm, unsigned long hpa,
 			return true;
 		}
 	}
+	rcu_read_unlock();
 
 	return false;
 }