powerpc/32: Remove PAGE_KERNEL_TEXT to fix startup failure

PAGE_KERNEL_TEXT is an old macro that is used to tell kernel whether
kernel text has to be mapped read-only or read-write based on build
time options.

But nowadays, with functionnalities like jump_labels, static links,
etc ... more only less all kernels need to be read-write at some
point, and some combinations of configs failed to work due to
innacurate setting of PAGE_KERNEL_TEXT. On the other hand, today
we have CONFIG_STRICT_KERNEL_RWX which implements a more controlled
access to kernel modifications.

Instead of trying to keep PAGE_KERNEL_TEXT accurate with all
possible options that may imply kernel text modification, always
set kernel text read-write at startup and rely on
CONFIG_STRICT_KERNEL_RWX to provide accurate protection.

Do this by passing PAGE_KERNEL_X to map_kernel_page() in
__maping_ram_chunk() instead of passing PAGE_KERNEL_TEXT. Once
this is done, the only remaining user of PAGE_KERNEL_TEXT is
mmu_mark_initmem_nx() which uses it in a call to setibat().
As setibat() ignores the RW/RO, we can seamlessly replace
PAGE_KERNEL_TEXT by PAGE_KERNEL_X here as well and get rid of
PAGE_KERNEL_TEXT completely.

Reported-by: Erhard Furtner <erhard_f@mailbox.org>
Closes: https://lore.kernel.org/all/342b4120-911c-4723-82ec-d8c9b03a8aef@mailbox.org/
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Tested-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/8e2d793abf87ae3efb8f6dce10f974ac0eda61b8.1757412205.git.christophe.leroy@csgroup.eu

Author: chleroy

arch/powerpc/include/asm/pgtable.h

@@ -20,18 +20,6 @@ struct mm_struct;
 #include <asm/nohash/pgtable.h>
 #endif /* !CONFIG_PPC_BOOK3S */
 
-/*
- * Protection used for kernel text. We want the debuggers to be able to
- * set breakpoints anywhere, so don't write protect the kernel text
- * on platforms where such control is possible.
- */
-#if defined(CONFIG_KGDB) || defined(CONFIG_XMON) || defined(CONFIG_BDI_SWITCH) || \
-	defined(CONFIG_KPROBES) || defined(CONFIG_DYNAMIC_FTRACE)
-#define PAGE_KERNEL_TEXT	PAGE_KERNEL_X
-#else
-#define PAGE_KERNEL_TEXT	PAGE_KERNEL_ROX
-#endif
-
 /* Make modules code happy. We don't set RO yet */
 #define PAGE_KERNEL_EXEC	PAGE_KERNEL_X
 

arch/powerpc/mm/book3s32/mmu.c

@@ -204,7 +204,7 @@ int mmu_mark_initmem_nx(void)
 
 	for (i = 0; i < nb - 1 && base < top;) {
 		size = bat_block_size(base, top);
-		setibat(i++, PAGE_OFFSET + base, base, size, PAGE_KERNEL_TEXT);
+		setibat(i++, PAGE_OFFSET + base, base, size, PAGE_KERNEL_X);
 		base += size;
 	}
 	if (base < top) {
@@ -215,7 +215,7 @@ int mmu_mark_initmem_nx(void)
 				pr_warn("Some RW data is getting mapped X. "
 					"Adjust CONFIG_DATA_SHIFT to avoid that.\n");
 		}
-		setibat(i++, PAGE_OFFSET + base, base, size, PAGE_KERNEL_TEXT);
+		setibat(i++, PAGE_OFFSET + base, base, size, PAGE_KERNEL_X);
 		base += size;
 	}
 	for (; i < nb; i++)

arch/powerpc/mm/pgtable_32.c

@@ -104,7 +104,7 @@ static void __init __mapin_ram_chunk(unsigned long offset, unsigned long top)
 	p = memstart_addr + s;
 	for (; s < top; s += PAGE_SIZE) {
 		ktext = core_kernel_text(v);
-		map_kernel_page(v, p, ktext ? PAGE_KERNEL_TEXT : PAGE_KERNEL);
+		map_kernel_page(v, p, ktext ? PAGE_KERNEL_X : PAGE_KERNEL);
 		v += PAGE_SIZE;
 		p += PAGE_SIZE;
 	}