powerpc: move __end_rodata to cover arch read-only sections

powerpc has a number of read-only sections and tables that are put after
RO_DATA(). Move the __end_rodata symbol to cover these as well.

Setting memory to read-only at boot is done using __init_begin, change
that to use __end_rodata.

This makes is_kernel_rodata() exactly cover the read-only region, as
well as other things using __end_rodata (e.g., kernel/dma/debug.c).
Boot dmesg also prints the rodata size more accurately.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220916040755.2398112-2-npiggin@gmail.com

arch/powerpc/kernel/vmlinux.lds.S

@@ -219,6 +219,7 @@ SECTIONS
 	 */
 	. = ALIGN(STRICT_ALIGN_SIZE);
 	__srwx_boundary = .;
+	__end_rodata = .;
 	__init_begin = .;
 
 /*

arch/powerpc/mm/book3s32/mmu.c

@@ -240,7 +240,7 @@ void mmu_mark_rodata_ro(void)
 	for (i = 0; i < nb; i++) {
 		struct ppc_bat *bat = BATS[i];
 
-		if (bat_addrs[i].start < (unsigned long)__init_begin)
+		if (bat_addrs[i].start < (unsigned long)__end_rodata)
 			bat[1].batl = (bat[1].batl & ~BPP_RW) | BPP_RX;
 	}
 

arch/powerpc/mm/book3s64/hash_pgtable.c

@@ -541,7 +541,7 @@ void hash__mark_rodata_ro(void)
 	unsigned long start, end, pp;
 
 	start = (unsigned long)_stext;
-	end = (unsigned long)__init_begin;
+	end = (unsigned long)__end_rodata;
 
 	pp = htab_convert_pte_flags(pgprot_val(PAGE_KERNEL_ROX), HPTE_USE_KERNEL_KEY);
 

arch/powerpc/mm/book3s64/radix_pgtable.c

@@ -228,7 +228,7 @@ void radix__mark_rodata_ro(void)
 	unsigned long start, end;
 
 	start = (unsigned long)_stext;
-	end = (unsigned long)__init_begin;
+	end = (unsigned long)__end_rodata;
 
 	radix__change_memory_range(start, end, _PAGE_WRITE);
 }

arch/powerpc/mm/pgtable_32.c

@@ -158,10 +158,11 @@ void mark_rodata_ro(void)
 	}
 
 	/*
-	 * mark .text and .rodata as read only. Use __init_begin rather than
-	 * __end_rodata to cover NOTES and EXCEPTION_TABLE.
+	 * mark text and rodata as read only. __end_rodata is set by
+	 * powerpc's linker script and includes tables and data
+	 * requiring relocation which are not put in RO_DATA.
 	 */
-	numpages = PFN_UP((unsigned long)__init_begin) -
+	numpages = PFN_UP((unsigned long)__end_rodata) -
 		   PFN_DOWN((unsigned long)_stext);
 
 	set_memory_ro((unsigned long)_stext, numpages);