powerpc/chrp: Fix enter_rtas() with CONFIG_VMAP_STACK

With CONFIG_VMAP_STACK, data MMU has to be enabled
to read data on the stack.

Fixes: cd08f109 ("powerpc/32s: Enable CONFIG_VMAP_STACK")
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/d2330584f8c42d3039896e2b56f5d39676dc919c.1581669558.git.christophe.leroy@c-s.fr

arch/powerpc/kernel/entry_32.S

@@ -1354,12 +1354,17 @@ _GLOBAL(enter_rtas)
 	mtspr	SPRN_SRR0,r8
 	mtspr	SPRN_SRR1,r9
 	RFI
-1:	tophys(r9,r1)
+1:	tophys_novmstack r9, r1
+#ifdef CONFIG_VMAP_STACK
+	li	r0, MSR_KERNEL & ~MSR_IR	/* can take DTLB miss */
+	mtmsr	r0
+	isync
+#endif
 	lwz	r8,INT_FRAME_SIZE+4(r9)	/* get return address */
 	lwz	r9,8(r9)	/* original msr value */
 	addi	r1,r1,INT_FRAME_SIZE
 	li	r0,0
-	tophys(r7, r2)
+	tophys_novmstack r7, r2
 	stw	r0, THREAD + RTAS_SP(r7)
 	mtspr	SPRN_SRR0,r8
 	mtspr	SPRN_SRR1,r9