Unverified Commit c78f94f3 authored by Atish Patra's avatar Atish Patra Committed by Palmer Dabbelt
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RISC-V: Use __cpu_up_stack/task_pointer only for spinwait method 



The __cpu_up_stack/task_pointer array is only used for spinwait method
now. The per cpu array based lookup is also fragile for platforms with
discontiguous/sparse hartids. The spinwait method is only used for
M-mode Linux or older firmwares without SBI HSM extension. For general
Linux systems, ordered booting method is preferred anyways to support
cpu hotplug and kexec.

Make sure that __cpu_up_stack/task_pointer is only used for spinwait
method. Take this opportunity to rename it to
__cpu_spinwait_stack/task_pointer to emphasize the purpose as well.

Reviewed-by: default avatarAnup Patel <anup@brainfault.org>
Signed-off-by: default avatarAtish Patra <atishp@rivosinc.com>
Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent 410bb20a

arch/riscv/include/asm/cpu_ops.h

+0 −2
Original line number Diff line number Diff line
@@ -40,7 +40,5 @@ struct cpu_operations { 


extern const struct cpu_operations *cpu_ops[NR_CPUS];

void __init cpu_set_ops(int cpu);

void cpu_update_secondary_bootdata(unsigned int cpuid,

				   struct task_struct *tidle);



#endif /* ifndef __ASM_CPU_OPS_H */

arch/riscv/kernel/cpu_ops.c

+0 −16
Original line number Diff line number Diff line
@@ -8,31 +8,15 @@ 
#include <linux/of.h>

#include <linux/string.h>

#include <linux/sched.h>

#include <linux/sched/task_stack.h>

#include <asm/cpu_ops.h>

#include <asm/sbi.h>

#include <asm/smp.h>



const struct cpu_operations *cpu_ops[NR_CPUS] __ro_after_init;



void *__cpu_up_stack_pointer[NR_CPUS] __section(".data");

void *__cpu_up_task_pointer[NR_CPUS] __section(".data");



extern const struct cpu_operations cpu_ops_sbi;

extern const struct cpu_operations cpu_ops_spinwait;



void cpu_update_secondary_bootdata(unsigned int cpuid,

				   struct task_struct *tidle)

{

	int hartid = cpuid_to_hartid_map(cpuid);



	/* Make sure tidle is updated */

	smp_mb();

	WRITE_ONCE(__cpu_up_stack_pointer[hartid],

		   task_stack_page(tidle) + THREAD_SIZE);

	WRITE_ONCE(__cpu_up_task_pointer[hartid], tidle);

}



void __init cpu_set_ops(int cpuid)

{

#if IS_ENABLED(CONFIG_RISCV_SBI)

arch/riscv/kernel/cpu_ops_spinwait.c

+26 −1
Original line number Diff line number Diff line
@@ -6,11 +6,36 @@ 
#include <linux/errno.h>

#include <linux/of.h>

#include <linux/string.h>

#include <linux/sched/task_stack.h>

#include <asm/cpu_ops.h>

#include <asm/sbi.h>

#include <asm/smp.h>



const struct cpu_operations cpu_ops_spinwait;

void *__cpu_spinwait_stack_pointer[NR_CPUS] __section(".data");

void *__cpu_spinwait_task_pointer[NR_CPUS] __section(".data");



static void cpu_update_secondary_bootdata(unsigned int cpuid,

				   struct task_struct *tidle)

{

	int hartid = cpuid_to_hartid_map(cpuid);



	/*

	 * The hartid must be less than NR_CPUS to avoid out-of-bound access

	 * errors for __cpu_spinwait_stack/task_pointer. That is not always possible

	 * for platforms with discontiguous hartid numbering scheme. That's why

	 * spinwait booting is not the recommended approach for any platforms

	 * booting Linux in S-mode and can be disabled in the future.

	 */

	if (hartid == INVALID_HARTID || hartid >= NR_CPUS)

		return;



	/* Make sure tidle is updated */

	smp_mb();

	WRITE_ONCE(__cpu_spinwait_stack_pointer[hartid],

		   task_stack_page(tidle) + THREAD_SIZE);

	WRITE_ONCE(__cpu_spinwait_task_pointer[hartid], tidle);

}



static int spinwait_cpu_prepare(unsigned int cpuid)

{
@@ -28,7 +53,7 @@ static int spinwait_cpu_start(unsigned int cpuid, struct task_struct *tidle) 
	 * selects the first cpu to boot the kernel and causes the remainder

	 * of the cpus to spin in a loop waiting for their stack pointer to be

	 * setup by that main cpu.  Writing to bootdata

	 * (i.e __cpu_up_stack_pointer) signals to the spinning cpus that they

	 * (i.e __cpu_spinwait_stack_pointer) signals to the spinning cpus that they

	 * can continue the boot process.

	 */

	cpu_update_secondary_bootdata(cpuid, tidle);

arch/riscv/kernel/head.S

+2 −2
Original line number Diff line number Diff line
@@ -347,9 +347,9 @@ clear_bss_done: 
	csrw CSR_TVEC, a3



	slli a3, a0, LGREG

	la a1, __cpu_up_stack_pointer

	la a1, __cpu_spinwait_stack_pointer

	XIP_FIXUP_OFFSET a1

	la a2, __cpu_up_task_pointer

	la a2, __cpu_spinwait_task_pointer

	XIP_FIXUP_OFFSET a2

	add a1, a3, a1

	add a2, a3, a2

arch/riscv/kernel/head.h

+2 −2
Original line number Diff line number Diff line
@@ -16,7 +16,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa); 
asmlinkage void __init __copy_data(void);

#endif



extern void *__cpu_up_stack_pointer[];

extern void *__cpu_up_task_pointer[];

extern void *__cpu_spinwait_stack_pointer[];

extern void *__cpu_spinwait_task_pointer[];



#endif /* __ASM_HEAD_H */