powerpc: allow minimum sized kernel stack frames

This affects only 64-bit ELFv2 kernels, and reduces the minimum
asm-created stack frame size from 112 to 32 byte on those kernels.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221127124942.1665522-16-npiggin@gmail.com

arch/powerpc/kernel/head_40x.S

@@ -602,7 +602,7 @@ start_here:
 	lis	r1,init_thread_union@ha
 	addi	r1,r1,init_thread_union@l
 	li	r0,0
-	stwu	r0,THREAD_SIZE-STACK_FRAME_OVERHEAD(r1)
+	stwu	r0,THREAD_SIZE-STACK_FRAME_MIN_SIZE(r1)
 
 	bl	early_init	/* We have to do this with MMU on */
 

arch/powerpc/kernel/head_44x.S

@@ -109,7 +109,7 @@ _GLOBAL(_start);
 	lis	r1,init_thread_union@h
 	ori	r1,r1,init_thread_union@l
 	li	r0,0
-	stwu	r0,THREAD_SIZE-STACK_FRAME_OVERHEAD(r1)
+	stwu	r0,THREAD_SIZE-STACK_FRAME_MIN_SIZE(r1)
 
 	bl	early_init
 
@@ -1012,7 +1012,7 @@ _GLOBAL(start_secondary_47x)
 	 */
 	lis	r1,temp_boot_stack@h
 	ori	r1,r1,temp_boot_stack@l
-	addi	r1,r1,1024-STACK_FRAME_OVERHEAD
+	addi	r1,r1,1024-STACK_FRAME_MIN_SIZE
 	li	r0,0
 	stw	r0,0(r1)
 	bl	mmu_init_secondary
@@ -1025,7 +1025,7 @@ _GLOBAL(start_secondary_47x)
 	lwz	r1,TASK_STACK(r2)
 
 	/* Current stack pointer */
-	addi	r1,r1,THREAD_SIZE-STACK_FRAME_OVERHEAD
+	addi	r1,r1,THREAD_SIZE-STACK_FRAME_MIN_SIZE
 	li	r0,0
 	stw	r0,0(r1)
 

arch/powerpc/kernel/head_64.S

@@ -424,7 +424,7 @@ generic_secondary_common_init:
 
 	/* Create a temp kernel stack for use before relocation is on.	*/
 	ld	r1,PACAEMERGSP(r13)
-	subi	r1,r1,STACK_FRAME_OVERHEAD
+	subi	r1,r1,STACK_FRAME_MIN_SIZE
 
 	/* See if we need to call a cpu state restore handler */
 	LOAD_REG_ADDR(r23, cur_cpu_spec)
@@ -780,7 +780,7 @@ _GLOBAL(pmac_secondary_start)
 
 	/* Create a temp kernel stack for use before relocation is on.	*/
 	ld	r1,PACAEMERGSP(r13)
-	subi	r1,r1,STACK_FRAME_OVERHEAD
+	subi	r1,r1,STACK_FRAME_MIN_SIZE
 
 	b	__secondary_start
 
@@ -958,7 +958,7 @@ start_here_multiplatform:
 	LOAD_REG_IMMEDIATE(r1,THREAD_SIZE)
 	add	r1,r3,r1
 	li	r0,0
-	stdu	r0,-STACK_FRAME_OVERHEAD(r1)
+	stdu	r0,-STACK_FRAME_MIN_SIZE(r1)
 
 	/*
 	 * Do very early kernel initializations, including initial hash table

arch/powerpc/kernel/head_85xx.S

@@ -229,7 +229,7 @@ set_ivor:
 	lis	r1,init_thread_union@h
 	ori	r1,r1,init_thread_union@l
 	li	r0,0
-	stwu	r0,THREAD_SIZE-STACK_FRAME_OVERHEAD(r1)
+	stwu	r0,THREAD_SIZE-STACK_FRAME_MIN_SIZE(r1)
 
 #ifdef CONFIG_SMP
 	stw	r24, TASK_CPU(r2)
@@ -1044,7 +1044,7 @@ __secondary_start:
 	lwz	r1,TASK_STACK(r2)
 
 	/* stack */
-	addi	r1,r1,THREAD_SIZE-STACK_FRAME_OVERHEAD
+	addi	r1,r1,THREAD_SIZE-STACK_FRAME_MIN_SIZE
 	li	r0,0
 	stw	r0,0(r1)
 

arch/powerpc/kernel/head_8xx.S

@@ -537,7 +537,7 @@ start_here:
 	ori	r0, r0, STACK_END_MAGIC@l
 	stw	r0, 0(r1)
 	li	r0,0
-	stwu	r0,THREAD_SIZE-STACK_FRAME_OVERHEAD(r1)
+	stwu	r0,THREAD_SIZE-STACK_FRAME_MIN_SIZE(r1)
 
 	lis	r6, swapper_pg_dir@ha
 	tophys(r6,r6)

arch/powerpc/kernel/head_book3s_32.S

@@ -840,7 +840,7 @@ __secondary_start:
 	lwz	r1,TASK_STACK(r1)
 
 	/* stack */
-	addi	r1,r1,THREAD_SIZE-STACK_FRAME_OVERHEAD
+	addi	r1,r1,THREAD_SIZE-STACK_FRAME_MIN_SIZE
 	li	r0,0
 	tophys(r3,r1)
 	stw	r0,0(r3)
@@ -966,7 +966,7 @@ END_MMU_FTR_SECTION_IFCLR(MMU_FTR_HPTE_TABLE)
 	lis	r1,init_thread_union@ha
 	addi	r1,r1,init_thread_union@l
 	li	r0,0
-	stwu	r0,THREAD_SIZE-STACK_FRAME_OVERHEAD(r1)
+	stwu	r0,THREAD_SIZE-STACK_FRAME_MIN_SIZE(r1)
 /*
  * Do early platform-specific initialization,
  * and set up the MMU.

arch/powerpc/kernel/irq.c

@@ -210,7 +210,7 @@ static __always_inline void call_do_softirq(const void *sp)
 		 PPC_LL "	%%r1, 0(%%r1)		;"
 		 : // Outputs
 		 : // Inputs
-		   [sp] "b" (sp), [offset] "i" (THREAD_SIZE - STACK_FRAME_OVERHEAD),
+		   [sp] "b" (sp), [offset] "i" (THREAD_SIZE - STACK_FRAME_MIN_SIZE),
 		   [callee] "i" (__do_softirq)
 		 : // Clobbers
 		   "lr", "xer", "ctr", "memory", "cr0", "cr1", "cr5", "cr6",
@@ -264,7 +264,7 @@ static __always_inline void call_do_irq(struct pt_regs *regs, void *sp)
 		 : // Outputs
 		   "+r" (r3)
 		 : // Inputs
-		   [sp] "b" (sp), [offset] "i" (THREAD_SIZE - STACK_FRAME_OVERHEAD),
+		   [sp] "b" (sp), [offset] "i" (THREAD_SIZE - STACK_FRAME_MIN_SIZE),
 		   [callee] "i" (__do_irq)
 		 : // Clobbers
 		   "lr", "xer", "ctr", "memory", "cr0", "cr1", "cr5", "cr6",

arch/powerpc/kernel/misc_32.S

@@ -382,7 +382,7 @@ EXPORT_SYMBOL(__bswapdi2)
 _GLOBAL(start_secondary_resume)
 	/* Reset stack */
 	rlwinm	r1, r1, 0, 0, 31 - THREAD_SHIFT
-	addi	r1,r1,THREAD_SIZE-STACK_FRAME_OVERHEAD
+	addi	r1,r1,THREAD_SIZE-STACK_FRAME_MIN_SIZE
 	li	r3,0
 	stw	r3,0(r1)		/* Zero the stack frame pointer	*/
 	bl	start_secondary

arch/powerpc/kernel/misc_64.S

@@ -384,7 +384,7 @@ _GLOBAL(kexec_sequence)
 	std	r0,16(r1)
 
 	/* switch stacks to newstack -- &kexec_stack.stack */
-	stdu	r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r3)
+	stdu	r1,THREAD_SIZE-STACK_FRAME_MIN_SIZE(r3)
 	mr	r1,r3
 
 	li	r0,0
@@ -401,7 +401,7 @@ _GLOBAL(kexec_sequence)
 	std	r26,-48(r1)
 	std	r25,-56(r1)
 
-	stdu	r1,-STACK_FRAME_OVERHEAD-64(r1)
+	stdu	r1,-STACK_FRAME_MIN_SIZE-64(r1)
 
 	/* save args into preserved regs */
 	mr	r31,r3			/* newstack (both) */

arch/powerpc/kernel/process.c

@@ -2180,7 +2180,7 @@ int validate_sp_size(unsigned long sp, struct task_struct *p,
 
 int validate_sp(unsigned long sp, struct task_struct *p)
 {
-	return validate_sp_size(sp, p, STACK_FRAME_OVERHEAD);
+	return validate_sp_size(sp, p, STACK_FRAME_MIN_SIZE);
 }
 
 static unsigned long ___get_wchan(struct task_struct *p)

arch/powerpc/kernel/smp.c

@@ -1249,7 +1249,7 @@ static void cpu_idle_thread_init(unsigned int cpu, struct task_struct *idle)
 #ifdef CONFIG_PPC64
 	paca_ptrs[cpu]->__current = idle;
 	paca_ptrs[cpu]->kstack = (unsigned long)task_stack_page(idle) +
-				 THREAD_SIZE - STACK_FRAME_OVERHEAD;
+				 THREAD_SIZE - STACK_FRAME_MIN_SIZE;
 #endif
 	task_thread_info(idle)->cpu = cpu;
 	secondary_current = current_set[cpu] = idle;

arch/powerpc/kernel/stacktrace.c

@@ -94,7 +94,7 @@ int __no_sanitize_address arch_stack_walk_reliable(stack_trace_consume_fn consum
 		 * idle tasks have a custom stack layout,
 		 * c.f. cpu_idle_thread_init().
 		 */
-		stack_end -= STACK_FRAME_OVERHEAD;
+		stack_end -= STACK_FRAME_MIN_SIZE;
 	}
 
 	if (task == current)