powerpc/6xx: Fix power_save_ppc32_restore() with CONFIG_VMAP_STACK

power_save_ppc32_restore() is called during exception entry, before
re-enabling the MMU. It substracts KERNELBASE from the address
of nap_save_msscr0 to access it.

With CONFIG_VMAP_STACK enabled, data MMU translation has already been
re-enabled, so power_save_ppc32_restore() has to access
nap_save_msscr0 by its virtual address.

Reported-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Fixes: cd08f109e2 ("powerpc/32s: Enable CONFIG_VMAP_STACK")
Tested-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/7bce32ccbab3ba3e3e0f27da6961bf6313df97ed.1581663140.git.christophe.leroy@c-s.fr

arch/powerpc/kernel/idle_6xx.S

@@ -166,7 +166,11 @@ BEGIN_FTR_SECTION
 	mfspr	r9,SPRN_HID0
 	andis.	r9,r9,HID0_NAP@h
 	beq	1f
+#ifdef CONFIG_VMAP_STACK
+	addis	r9, r11, nap_save_msscr0@ha
+#else
 	addis	r9,r11,(nap_save_msscr0-KERNELBASE)@ha
+#endif
 	lwz	r9,nap_save_msscr0@l(r9)
 	mtspr	SPRN_MSSCR0, r9
 	sync
@@ -174,7 +178,11 @@ BEGIN_FTR_SECTION
 1:
 END_FTR_SECTION_IFSET(CPU_FTR_NAP_DISABLE_L2_PR)
 BEGIN_FTR_SECTION
+#ifdef CONFIG_VMAP_STACK
+	addis	r9, r11, nap_save_hid1@ha
+#else
 	addis	r9,r11,(nap_save_hid1-KERNELBASE)@ha
+#endif
 	lwz	r9,nap_save_hid1@l(r9)
 	mtspr	SPRN_HID1, r9
 END_FTR_SECTION_IFSET(CPU_FTR_DUAL_PLL_750FX)