[PATCH 3/8] powerpc: use switch frame for ret_from_kernel_thread parameters
Nicholas Piggin
npiggin at gmail.com
Wed Feb 1 03:55:29 AEDT 2023
The kernel thread path in copy_thread creates a user interrupt frame on
stack and stores the function and arg parameters there, and
ret_from_kernel_thread loads them. This is a slightly confusing way to
overload that frame. Non-volatile registers are loaded from the switch
frame, so the parameters can be stored there.
Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
arch/powerpc/kernel/entry_32.S | 1 -
arch/powerpc/kernel/interrupt_64.S | 1 -
arch/powerpc/kernel/process.c | 9 +++++++++
3 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 755408c63be8..c3fdb3081d3d 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -188,7 +188,6 @@ ret_from_fork:
.globl ret_from_kernel_thread
ret_from_kernel_thread:
- REST_NVGPRS(r1)
bl schedule_tail
mtctr r14
mr r3,r15
diff --git a/arch/powerpc/kernel/interrupt_64.S b/arch/powerpc/kernel/interrupt_64.S
index fccc34489add..d60e7e7564df 100644
--- a/arch/powerpc/kernel/interrupt_64.S
+++ b/arch/powerpc/kernel/interrupt_64.S
@@ -741,7 +741,6 @@ _GLOBAL(ret_from_fork)
_GLOBAL(ret_from_kernel_thread)
bl schedule_tail
- REST_NVGPRS(r1)
mtctr r14
mr r3,r15
#ifdef CONFIG_PPC64_ELF_ABI_V2
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index dc66ca668b44..6cea224b7e60 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1812,6 +1812,15 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
((unsigned long *)sp)[0] = sp + STACK_SWITCH_FRAME_SIZE;
kregs = (struct pt_regs *)(sp + STACK_SWITCH_FRAME_REGS);
kregs->nip = ppc_function_entry(f);
+ if (unlikely(args->fn)) {
+ /*
+ * Put kthread create details in non-volatile GPRs in the
+ * switch frame so they are loaded by _switch before it
+ * returns to ret_from_kernel_thread.
+ */
+ kregs->gpr[14] = ppc_function_entry((void *)args->fn);
+ kregs->gpr[15] = (unsigned long)args->fn_arg;
+ }
p->thread.ksp = sp;
#ifdef CONFIG_HAVE_HW_BREAKPOINT
--
2.37.2
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