[PATCH v2 5/6] riscv: Use separate IRQ shadow call stacks

Sami Tolvanen
2023-08-15T20:34:56Z

When both CONFIG_IRQ_STACKS and SCS are enabled, also use a separate
per-CPU shadow call stack.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
arch/riscv/include/asm/scs.h | 7 +++++++
arch/riscv/kernel/entry.S | 7 +++++++
arch/riscv/kernel/irq.c | 21 +++++++++++++++++++++
3 files changed, 35 insertions(+)

diff --git a/arch/riscv/include/asm/scs.h b/arch/riscv/include/asm/scs.h
index 94726ea773e3..0e45db78b24b 100644
--- a/arch/riscv/include/asm/scs.h
+++ b/arch/riscv/include/asm/scs.h
@@ -13,6 +13,11 @@
XIP_FIXUP_OFFSET gp
.endm

+/* Load the per-CPU IRQ shadow call stack to gp. */
+.macro scs_load_irq_stack tmp
+ load_per_cpu gp, irq_shadow_call_stack_ptr, \tmp
+.endm
+
/* Load task_scs_sp(current) to gp. */
.macro scs_load_current
REG_L gp, TASK_TI_SCS_SP(tp)
@@ -34,6 +39,8 @@

.macro scs_load_init_stack
.endm
+.macro scs_load_irq_stack tmp
+.endm
.macro scs_load_current
.endm
.macro scs_load_current_if_task_changed prev
diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index ad34507d3c96..c86b76584d2d 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -238,12 +238,19 @@ SYM_FUNC_START(call_on_irq_stack)
REG_S s0, (sp)
addi s0, sp, 2*RISCV_SZPTR

+ /* Switch to the per-CPU shadow call stack */
+ scs_save_current
+ scs_load_irq_stack t0
+
/* 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 shadow call stack */
+ scs_load_current
+
/* Switch back to the thread stack and restore ra and s0 */
addi sp, s0, -2*RISCV_SZPTR
REG_L s0, (sp)
diff --git a/arch/riscv/kernel/irq.c b/arch/riscv/kernel/irq.c
index 95dafdcbd135..7bfea97ee7e7 100644
--- a/arch/riscv/kernel/irq.c
+++ b/arch/riscv/kernel/irq.c
@@ -9,6 +9,7 @@
#include <linux/irqchip.h>
#include <linux/irqdomain.h>
#include <linux/module.h>
+#include <linux/scs.h>
#include <linux/seq_file.h>
#include <asm/sbi.h>
#include <asm/smp.h>
@@ -34,6 +35,24 @@ EXPORT_SYMBOL_GPL(riscv_get_intc_hwnode);
#ifdef CONFIG_IRQ_STACKS
#include <asm/irq_stack.h>

+DECLARE_PER_CPU(ulong *, irq_shadow_call_stack_ptr);
+
+#ifdef CONFIG_SHADOW_CALL_STACK
+DEFINE_PER_CPU(ulong *, irq_shadow_call_stack_ptr);
+#endif
+
+static void init_irq_scs(void)
+{
+ int cpu;
+
+ if (!scs_is_enabled())
+ return;
+
+ for_each_possible_cpu(cpu)
+ per_cpu(irq_shadow_call_stack_ptr, cpu) =
+ scs_alloc(cpu_to_node(cpu));
+}
+
DEFINE_PER_CPU(ulong *, irq_stack_ptr);

#ifdef CONFIG_VMAP_STACK
@@ -76,6 +95,7 @@ void do_softirq_own_stack(void)
#endif /* CONFIG_HAVE_SOFTIRQ_ON_OWN_STACK */

#else
+static void init_irq_scs(void) {}
static void init_irq_stacks(void) {}
#endif /* CONFIG_IRQ_STACKS */

@@ -87,6 +107,7 @@ int arch_show_interrupts(struct seq_file *p, int prec)

void __init init_IRQ(void)
{
+ init_irq_scs();
init_irq_stacks();
irqchip_init();
if (!handle_arch_irq)
--
2.41.0.694.ge786442a9b-goog