MIPS: VDSO: Prevent use of smp_processor_id()

VDSO code should not be using smp_processor_id(), since it is executed
in user mode.
Introduce a VDSO-specific path which will cause a compile-time
or link-time error (depending upon support for __compiletime_error) if
the VDSO ever incorrectly attempts to use smp_processor_id().

[Matt Redfearn <matt.redfearn@imgtec.com>: Move before change to
smp_processor_id in series]

Signed-off-by: Paul Burton <paul.burton@mips.com>
Signed-off-by: Matt Redfearn <matt.redfearn@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/17932/
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@linux-mips.org

arch/mips/include/asm/smp.h

@@ -25,7 +25,17 @@ extern cpumask_t cpu_sibling_map[];
 extern cpumask_t cpu_core_map[];
 extern cpumask_t cpu_foreign_map[];
 
-#define raw_smp_processor_id() (current_thread_info()->cpu)
+static inline int raw_smp_processor_id(void)
+{
+#if defined(__VDSO__)
+	extern int vdso_smp_processor_id(void)
+		__compiletime_error("VDSO should not call smp_processor_id()");
+	return vdso_smp_processor_id();
+#else
+	return current_thread_info()->cpu;
+#endif
+}
+#define raw_smp_processor_id raw_smp_processor_id
 
 /* Map from cpu id to sequential logical cpu number.  This will only
    not be idempotent when cpus failed to come on-line.	*/

arch/mips/vdso/Makefile

@@ -7,7 +7,8 @@ ccflags-vdso := \
 	$(filter -I%,$(KBUILD_CFLAGS)) \
 	$(filter -E%,$(KBUILD_CFLAGS)) \
 	$(filter -mmicromips,$(KBUILD_CFLAGS)) \
-	$(filter -march=%,$(KBUILD_CFLAGS))
+	$(filter -march=%,$(KBUILD_CFLAGS)) \
+	-D__VDSO__
 cflags-vdso := $(ccflags-vdso) \
 	$(filter -W%,$(filter-out -Wa$(comma)%,$(KBUILD_CFLAGS))) \
 	-O2 -g -fPIC -fno-strict-aliasing -fno-common -fno-builtin -G 0 \