xtensa: enable context tracking

Put user exit context tracking call on the common kernel entry/exit path
(function calls are impossible at earlier kernel entry stages because
PS.EXCM is not cleared yet). Put user entry context tracking call on the
user exit path. Syscalls go through this common code too, so nothing
specific needs to be done for them.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

Documentation/features/time/context-tracking/arch-support.txt

@@ -27,5 +27,5 @@
     |       sparc: |  ok  |
     |          um: | TODO |
     |         x86: |  ok  |
-    |      xtensa: | TODO |
+    |      xtensa: |  ok  |
     -----------------------

arch/xtensa/Kconfig

@@ -31,6 +31,7 @@ config XTENSA
 	select HAVE_ARCH_KASAN if MMU && !XIP_KERNEL
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_ARCH_TRACEHOOK
+	select HAVE_CONTEXT_TRACKING
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DMA_CONTIGUOUS
 	select HAVE_EXIT_THREAD

arch/xtensa/kernel/entry.S

@@ -456,6 +456,12 @@ KABI_W	or	a3, a3, a2
 	beqz		abi_tmp0, 1f
 	abi_call	trace_hardirqs_off
 1:
+#endif
+#ifdef CONFIG_CONTEXT_TRACKING
+	l32i		abi_tmp0, a1, PT_PS
+	bbci.l		abi_tmp0, PS_UM_BIT, 1f
+	abi_call	context_tracking_user_exit
+1:
 #endif
 
 	/* Go to second-level dispatcher. Set up parameters to pass to the
@@ -540,6 +546,9 @@ common_exception_return:
 	j		.Lrestore_state
 
 .Lexit_tif_loop_user:
+#ifdef CONFIG_CONTEXT_TRACKING
+	abi_call	context_tracking_user_enter
+#endif
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
 	_bbci.l		abi_saved0, TIF_DB_DISABLED, 1f
 	abi_call	restore_dbreak