[PATCH 2/5] riscv: Deduplicate IRQ stack switching

Sami Tolvanen
2023-08-11T23:36:04Z

With CONFIG_IRQ_STACKS, we switch to a separate per-CPU IRQ stack
before calling handle_riscv_irq or __do_softirq. We currently
have duplicate inline assembly snippets for stack switching in
both code paths. Now that we can access per-CPU variables in
assembly, implement call_on_irq_stack in assembly, and use that
instead of redudant inline assembly.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
arch/riscv/include/asm/asm.h | 5 +++++
arch/riscv/include/asm/irq_stack.h | 3 +++
arch/riscv/kernel/entry.S | 32 ++++++++++++++++++++++++++++++
arch/riscv/kernel/irq.c | 32 ++++++++----------------------
arch/riscv/kernel/traps.c | 29 ++++-----------------------
5 files changed, 52 insertions(+), 49 deletions(-)

diff --git a/arch/riscv/include/asm/asm.h b/arch/riscv/include/asm/asm.h
index f403e46e04f2..13815a7f907a 100644
--- a/arch/riscv/include/asm/asm.h
+++ b/arch/riscv/include/asm/asm.h
@@ -98,6 +98,11 @@
add \dst, \dst, \tmp
.endm

+.macro load_per_cpu dst ptr tmp
+ asm_per_cpu \dst \ptr \tmp
+ REG_L \dst, 0(\dst)
+.endm
+
/* save all GPs except x1 ~ x5 */
.macro save_from_x6_to_x31
REG_S x6, PT_T1(sp)
diff --git a/arch/riscv/include/asm/irq_stack.h b/arch/riscv/include/asm/irq_stack.h
index e4042d297580..6441ded3b0cf 100644
--- a/arch/riscv/include/asm/irq_stack.h
+++ b/arch/riscv/include/asm/irq_stack.h
@@ -12,6 +12,9 @@

DECLARE_PER_CPU(ulong *, irq_stack_ptr);

+asmlinkage void call_on_irq_stack(struct pt_regs *regs,
+ void (*func)(struct pt_regs *));
+
#ifdef CONFIG_VMAP_STACK
/*
* To ensure that VMAP'd stack overflow detection works correctly, all VMAP'd
diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index 3d11aa3af105..39875f5e08a6 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -218,6 +218,38 @@ SYM_CODE_START(ret_from_fork)
tail syscall_exit_to_user_mode
SYM_CODE_END(ret_from_fork)

+#ifdef CONFIG_IRQ_STACKS
+/*
+ * void call_on_irq_stack(struct pt_regs *regs,
+ * void (*func)(struct pt_regs *));
+ *
+ * Calls func(regs) using the per-CPU IRQ stack.
+ */
+SYM_FUNC_START(call_on_irq_stack)
+ /* Create a frame record to save ra and s0 (fp) */
+ addi sp, sp, -RISCV_SZPTR
+ REG_S ra, (sp)
+ addi sp, sp, -RISCV_SZPTR
+ REG_S s0, (sp)
+ addi s0, sp, 2*RISCV_SZPTR
+
+ /* Switch to the per-CPU IRQ stack and call the handler */
+ load_per_cpu t0, irq_stack_ptr, t1
+ li t1, IRQ_STACK_SIZE
+ add sp, t0, t1
+ jalr a1
+
+ /* Switch back to the thread stack and restore ra and s0 */
+ addi sp, s0, -2*RISCV_SZPTR
+ REG_L s0, (sp)
+ addi sp, sp, RISCV_SZPTR
+ REG_L ra, (sp)
+ addi sp, sp, RISCV_SZPTR
+
+ ret
+SYM_FUNC_END(call_on_irq_stack)
+#endif /* CONFIG_IRQ_STACKS */
+
/*
* Integer register context switch
* The callee-saved registers must be saved and restored.
diff --git a/arch/riscv/kernel/irq.c b/arch/riscv/kernel/irq.c
index d0577cc6a081..95dafdcbd135 100644
--- a/arch/riscv/kernel/irq.c
+++ b/arch/riscv/kernel/irq.c
@@ -61,32 +61,16 @@ static void init_irq_stacks(void)
#endif /* CONFIG_VMAP_STACK */

#ifdef CONFIG_HAVE_SOFTIRQ_ON_OWN_STACK
+static void ___do_softirq(struct pt_regs *regs)
+{
+ __do_softirq();
+}
+
void do_softirq_own_stack(void)
{
-#ifdef CONFIG_IRQ_STACKS
- if (on_thread_stack()) {
- ulong *sp = per_cpu(irq_stack_ptr, smp_processor_id())
- + IRQ_STACK_SIZE/sizeof(ulong);
- __asm__ __volatile(
- "addi sp, sp, -"RISCV_SZPTR "\n"
- REG_S" ra, (sp) \n"
- "addi sp, sp, -"RISCV_SZPTR "\n"
- REG_S" s0, (sp) \n"
- "addi s0, sp, 2*"RISCV_SZPTR "\n"
- "move sp, %[sp] \n"
- "call __do_softirq \n"
- "addi sp, s0, -2*"RISCV_SZPTR"\n"
- REG_L" s0, (sp) \n"
- "addi sp, sp, "RISCV_SZPTR "\n"
- REG_L" ra, (sp) \n"
- "addi sp, sp, "RISCV_SZPTR "\n"
- :
- : [sp] "r" (sp)
- : "a0", "a1", "a2", "a3", "a4", "a5", "a6", "a7",
- "t0", "t1", "t2", "t3", "t4", "t5", "t6",
- "memory");
- } else
-#endif
+ if (on_thread_stack())
+ call_on_irq_stack(NULL, ___do_softirq);
+ else
__do_softirq();
}
#endif /* CONFIG_HAVE_SOFTIRQ_ON_OWN_STACK */
diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index deb2144d9143..83319b6816da 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -350,31 +350,10 @@ static void noinstr handle_riscv_irq(struct pt_regs *regs)
asmlinkage void noinstr do_irq(struct pt_regs *regs)
{
irqentry_state_t state = irqentry_enter(regs);
-#ifdef CONFIG_IRQ_STACKS
- if (on_thread_stack()) {
- ulong *sp = per_cpu(irq_stack_ptr, smp_processor_id())
- + IRQ_STACK_SIZE/sizeof(ulong);
- __asm__ __volatile(
- "addi sp, sp, -"RISCV_SZPTR "\n"
- REG_S" ra, (sp) \n"
- "addi sp, sp, -"RISCV_SZPTR "\n"
- REG_S" s0, (sp) \n"
- "addi s0, sp, 2*"RISCV_SZPTR "\n"
- "move sp, %[sp] \n"
- "move a0, %[regs] \n"
- "call handle_riscv_irq \n"
- "addi sp, s0, -2*"RISCV_SZPTR"\n"
- REG_L" s0, (sp) \n"
- "addi sp, sp, "RISCV_SZPTR "\n"
- REG_L" ra, (sp) \n"
- "addi sp, sp, "RISCV_SZPTR "\n"
- :
- : [sp] "r" (sp), [regs] "r" (regs)
- : "a0", "a1", "a2", "a3", "a4", "a5", "a6", "a7",
- "t0", "t1", "t2", "t3", "t4", "t5", "t6",
- "memory");
- } else
-#endif
+
+ if (IS_ENABLED(CONFIG_IRQ_STACKS) && on_thread_stack())
+ call_on_irq_stack(regs, handle_riscv_irq);
+ else
handle_riscv_irq(regs);

irqentry_exit(regs, state);
--
2.41.0.640.ga95def55d0-goog