Merge tag 'cpu-to-thread_info-v5.16-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull thread_info update to move 'cpu' back from task_struct from Kees Cook:
 "Cross-architecture update to move task_struct::cpu back into
  thread_info on arm64, x86, s390, powerpc, and riscv. All Acked by arch
  maintainers.

  Quoting Ard Biesheuvel:

     'Move task_struct::cpu back into thread_info

      Keeping CPU in task_struct is problematic for architectures that
      define raw_smp_processor_id() in terms of this field, as it
      requires linux/sched.h to be included, which causes a lot of pain
      in terms of circular dependencies (aka 'header soup')

      This series moves it back into thread_info (where it came from)
      for all architectures that enable THREAD_INFO_IN_TASK, addressing
      the header soup issue as well as some pointless differences in the
      implementations of task_cpu() and set_task_cpu()'"

* tag 'cpu-to-thread_info-v5.16-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  riscv: rely on core code to keep thread_info::cpu updated
  powerpc: smp: remove hack to obtain offset of task_struct::cpu
  sched: move CPU field back into thread_info if THREAD_INFO_IN_TASK=y
  powerpc: add CPU field to struct thread_info
  s390: add CPU field to struct thread_info
  x86: add CPU field to struct thread_info
  arm64: add CPU field to struct thread_info

5 files changed, 6 insertions, 31 deletions

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index aa6808e70647..54cad1faa5d0 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -446,17 +446,6 @@ else
 endif
 endif
 
-ifdef CONFIG_SMP
-ifdef CONFIG_PPC32
-prepare: task_cpu_prepare
-
-PHONY += task_cpu_prepare
-task_cpu_prepare: prepare0
-	$(eval KBUILD_CFLAGS += -D_TASK_CPU=$(shell awk '{if ($$2 == "TASK_CPU") print $$3;}' include/generated/asm-offsets.h))
-
-endif # CONFIG_PPC32
-endif # CONFIG_SMP
-
 PHONY += checkbin
 # Check toolchain versions:
 # - gcc-4.6 is the minimum kernel-wide version so nothing required.
diff --git a/arch/powerpc/include/asm/smp.h b/arch/powerpc/include/asm/smp.h
index 7ef1cd8168a0..007332a4a732 100644
--- a/arch/powerpc/include/asm/smp.h
+++ b/arch/powerpc/include/asm/smp.h
@@ -87,22 +87,7 @@ int is_cpu_dead(unsigned int cpu);
 /* 32-bit */
 extern int smp_hw_index[];
 
-/*
- * This is particularly ugly: it appears we can't actually get the definition
- * of task_struct here, but we need access to the CPU this task is running on.
- * Instead of using task_struct we're using _TASK_CPU which is extracted from
- * asm-offsets.h by kbuild to get the current processor ID.
- *
- * This also needs to be safeguarded when building asm-offsets.s because at
- * that time _TASK_CPU is not defined yet. It could have been guarded by
- * _TASK_CPU itself, but we want the build to fail if _TASK_CPU is missing
- * when building something else than asm-offsets.s
- */
-#ifdef GENERATING_ASM_OFFSETS
-#define raw_smp_processor_id()		(0)
-#else
-#define raw_smp_processor_id()		(*(unsigned int *)((void *)current + _TASK_CPU))
-#endif
+#define raw_smp_processor_id()		(current_thread_info()->cpu)
 #define hard_smp_processor_id() 	(smp_hw_index[smp_processor_id()])
 
 static inline int get_hard_smp_processor_id(int cpu)
diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
index b4ec6c7dd72e..5725029aaa29 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -47,6 +47,9 @@
 struct thread_info {
 	int		preempt_count;		/* 0 => preemptable,
 						   <0 => BUG */
+#ifdef CONFIG_SMP
+	unsigned int	cpu;
+#endif
 	unsigned long	local_flags;		/* private flags for thread */
 #ifdef CONFIG_LIVEPATCH
 	unsigned long *livepatch_sp;
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index e563d3222d69..cc05522f50bf 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -9,8 +9,6 @@
  * #defines from the assembly-language output.
  */
 
-#define GENERATING_ASM_OFFSETS	/* asm/smp.h */
-
 #include <linux/compat.h>
 #include <linux/signal.h>
 #include <linux/sched.h>
@@ -93,7 +91,7 @@ int main(void)
 #endif /* CONFIG_PPC64 */
 	OFFSET(TASK_STACK, task_struct, stack);
 #ifdef CONFIG_SMP
-	OFFSET(TASK_CPU, task_struct, cpu);
+	OFFSET(TASK_CPU, task_struct, thread_info.cpu);
 #endif
 
 #ifdef CONFIG_LIVEPATCH
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 605bab448f84..f7440f4eca2e 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -1223,7 +1223,7 @@ static void cpu_idle_thread_init(unsigned int cpu, struct task_struct *idle)
 	paca_ptrs[cpu]->kstack = (unsigned long)task_stack_page(idle) +
 				 THREAD_SIZE - STACK_FRAME_OVERHEAD;
 #endif
-	idle->cpu = cpu;
+	task_thread_info(idle)->cpu = cpu;
 	secondary_current = current_set[cpu] = idle;
 }