powerpc/vdso: Simplify __get_datapage()

The VDSO datapage and the text pages are always located immediately
next to each other, so it can be hardcoded without an indirection
through __kernel_datapage_offset

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/b08f5ef99d64cfc38f79b7ad5310d9b4d2479eeb.1601197618.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/vdso_datapage.h

@@ -105,10 +105,12 @@ extern struct vdso_arch_data *vdso_data;
 
 .macro get_datapage ptr, tmp
 	bcl	20, 31, .+4
+999:
 	mflr	\ptr
-	addi	\ptr, \ptr, (__kernel_datapage_offset - (.-4))@l
-	lwz	\tmp, 0(\ptr)
-	add	\ptr, \tmp, \ptr
+#if CONFIG_PPC_PAGE_SHIFT > 14
+	addis	\ptr, \ptr, (_vdso_datapage - 999b)@ha
+#endif
+	addi	\ptr, \ptr, (_vdso_datapage - 999b)@l
 .endm
 
 #endif /* __ASSEMBLY__ */

arch/powerpc/kernel/vdso32/vdso32.lds.S

@@ -4,6 +4,7 @@
  * library
  */
 #include <asm/vdso.h>
+#include <asm/page.h>
 
 #ifdef __LITTLE_ENDIAN__
 OUTPUT_FORMAT("elf32-powerpcle", "elf32-powerpcle", "elf32-powerpcle")
@@ -15,6 +16,7 @@ ENTRY(_start)
 
 SECTIONS
 {
+	PROVIDE(_vdso_datapage = . - PAGE_SIZE);
 	. = VDSO32_LBASE + SIZEOF_HEADERS;
 
 	.hash          	: { *(.hash) }			:text

arch/powerpc/kernel/vdso64/vdso64.lds.S

@@ -4,6 +4,7 @@
  * library
  */
 #include <asm/vdso.h>
+#include <asm/page.h>
 
 #ifdef __LITTLE_ENDIAN__
 OUTPUT_FORMAT("elf64-powerpcle", "elf64-powerpcle", "elf64-powerpcle")
@@ -15,6 +16,7 @@ ENTRY(_start)
 
 SECTIONS
 {
+	PROVIDE(_vdso_datapage = . - PAGE_SIZE);
 	. = VDSO64_LBASE + SIZEOF_HEADERS;
 
 	.hash		: { *(.hash) }			:text