// SPDX-License-Identifier: GPL-2.0
/*
 *      Copyright (C) 1992, 1998 Linus Torvalds, Ingo Molnar
 *
 * This file contains the lowest level x86-specific interrupt
 * entry, irq-stacks and irq statistics code. All the remaining
 * irq logic is done by the generic kernel/irq/ code and
 * by the x86-specific irq controller code. (e.g. i8259.c and
 * io_apic.c.)
 */

#include <linux/seq_file.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/kernel_stat.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/delay.h>
#include <linux/uaccess.h>
#include <linux/percpu.h>
#include <linux/mm.h>

#include <asm/apic.h>
#include <asm/nospec-branch.h>
#include <asm/softirq_stack.h>

#ifdef CONFIG_DEBUG_STACKOVERFLOW

int sysctl_panic_on_stackoverflow __read_mostly;

/* Debugging check for stack overflow: is there less than 1KB free? */
static bool check_stack_overflow(void)
{
        unsigned long sp = current_stack_pointer & (THREAD_SIZE - 1);

        return sp < (sizeof(struct thread_info) + STACK_WARN);
}

static void print_stack_overflow(void)
{
        printk(KERN_WARNING "low stack detected by irq handler\n");
        dump_stack();
        if (sysctl_panic_on_stackoverflow)
                panic("low stack detected by irq handler - check messages\n");
}

#else
static inline bool check_stack_overflow(void) { return false; }
static inline void print_stack_overflow(void) { }
#endif

DEFINE_PER_CPU_CACHE_HOT(struct irq_stack *, softirq_stack_ptr);

static void call_on_stack(void *func, void *stack)
{
        asm volatile("xchgl %[sp], %%esp\n"
                     CALL_NOSPEC
                     "movl %[sp], %%esp"
                     : [sp] "+b" (stack)
                     : [thunk_target] "D" (func)
                     : "memory", "cc", "edx", "ecx", "eax");
}

static inline void *current_stack(void)
{
        return (void *)(current_stack_pointer & ~(THREAD_SIZE - 1));
}

static inline bool execute_on_irq_stack(bool overflow, struct irq_desc *desc)
{
        struct irq_stack *curstk, *irqstk;
        u32 *isp, *prev_esp;

        curstk = (struct irq_stack *) current_stack();
        irqstk = __this_cpu_read(hardirq_stack_ptr);

        /*
         * this is where we switch to the IRQ stack. However, if we are
         * already using the IRQ stack (because we interrupted a hardirq
         * handler) we can't do that and just have to keep using the
         * current stack (which is the irq stack already after all)
         */
        if (unlikely(curstk == irqstk))
                return false;

        isp = (u32 *) ((char *)irqstk + sizeof(*irqstk));

        /* Save the next esp at the bottom of the stack */
        prev_esp = (u32 *)irqstk;
        *prev_esp = current_stack_pointer;

        if (unlikely(overflow))
                call_on_stack(print_stack_overflow, isp);

        asm volatile("xchgl %[sp], %%esp\n"
                     CALL_NOSPEC
                     "movl %[sp], %%esp"
                     : "+a" (desc), [sp] "+b" (isp)
                     : [thunk_target] "D" (desc->handle_irq)
                     : "memory", "cc", "edx", "ecx");
        return true;
}

/*
 * Allocate per-cpu stacks for hardirq and softirq processing
 */
int irq_init_percpu_irqstack(unsigned int cpu)
{
        int node = cpu_to_node(cpu);
        struct page *ph, *ps;

        if (per_cpu(hardirq_stack_ptr, cpu))
                return 0;

        ph = alloc_pages_node(node, THREADINFO_GFP, THREAD_SIZE_ORDER);
        if (!ph)
                return -ENOMEM;
        ps = alloc_pages_node(node, THREADINFO_GFP, THREAD_SIZE_ORDER);
        if (!ps) {
                __free_pages(ph, THREAD_SIZE_ORDER);
                return -ENOMEM;
        }

        per_cpu(hardirq_stack_ptr, cpu) = page_address(ph);
        per_cpu(softirq_stack_ptr, cpu) = page_address(ps);
        return 0;
}

#ifdef CONFIG_SOFTIRQ_ON_OWN_STACK
void do_softirq_own_stack(void)
{
        struct irq_stack *irqstk;
        u32 *isp, *prev_esp;

        irqstk = __this_cpu_read(softirq_stack_ptr);

        /* build the stack frame on the softirq stack */
        isp = (u32 *) ((char *)irqstk + sizeof(*irqstk));

        /* Push the previous esp onto the stack */
        prev_esp = (u32 *)irqstk;
        *prev_esp = current_stack_pointer;

        call_on_stack(__do_softirq, isp);
}
#endif

void __handle_irq(struct irq_desc *desc, struct pt_regs *regs)
{
        bool overflow = check_stack_overflow();

        if (user_mode(regs) || !execute_on_irq_stack(overflow, desc)) {
                if (unlikely(overflow))
                        print_stack_overflow();
                generic_handle_irq_desc(desc);
        }
}