diff --git a/arch/powerpc/mm/mmu_context_book3s64.c b/arch/powerpc/mm/mmu_context_book3s64.c
index b5288b460befcb2f3bf18744f2bb2f49cd31a13d..227b2a6c4544b1739813bf192e3a156bed7e1ffd 100644
--- a/arch/powerpc/mm/mmu_context_book3s64.c
+++ b/arch/powerpc/mm/mmu_context_book3s64.c
@@ -85,8 +85,17 @@ int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
 		/* The old code would re-promote on fork, we don't do that
 		 * when using slices as it could cause problem promoting slices
 		 * that have been forced down to 4K
+		 *
+		 * For book3s we have MMU_NO_CONTEXT set to be ~0. Hence check
+		 * explicitly against context.id == 0. This ensures that we
+		 * properly initialize context slice details for newly allocated
+		 * mm's (which will have id == 0) and don't alter context slice
+		 * inherited via fork (which will have id != 0).
+		 *
+		 * We should not be calling init_new_context() on init_mm. Hence a
+		 * check against 0 is ok.
 		 */
-		if (slice_mm_new_context(mm))
+		if (mm->context.id == 0)
 			slice_set_user_psize(mm, mmu_virtual_psize);
 		subpage_prot_init_new_context(mm);
 	}