powerpc/mm: Code cleanup for __hash_page_thp

This part was commented from commit 6d492ec
("powerpc/THP: Add code to handle HPTE faults for hugepages")
in about 11 years before.

If there are no plans to enable this part code in the future,
we can remove this dead code and replace with a comment
explaining what the dead code was trying to say.

Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Suggested-by: "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240301085834.1512921-1-chentao@kylinos.cn

Author: KunWuChan

arch/powerpc/mm/book3s64/hash_hugepage.c

@@ -59,16 +59,13 @@ int __hash_page_thp(unsigned long ea, unsigned long access, unsigned long vsid,
 
 	rflags = htab_convert_pte_flags(new_pmd, flags);
 
-#if 0
-	if (!cpu_has_feature(CPU_FTR_COHERENT_ICACHE)) {
+	/*
+	 * THPs are only supported on platforms that can do mixed page size
+	 * segments (MPSS) and all such platforms have coherent icache. Hence we
+	 * don't need to do lazy icache flush (hash_page_do_lazy_icache()) on
+	 * noexecute fault.
+	 */
 
-		/*
-		 * No CPU has hugepages but lacks no execute, so we
-		 * don't need to worry about that case
-		 */
-		rflags = hash_page_do_lazy_icache(rflags, __pte(old_pte), trap);
-	}
-#endif
 	/*
 	 * Find the slot index details for this ea, using base page size.
 	 */