// SPDX-License-Identifier: GPL-2.0
// Copyright (C) 2018 Hangzhou C-SKY Microsystems co.,ltd.

#include <linux/extable.h>
#include <linux/kprobes.h>
#include <linux/mmu_context.h>
#include <linux/perf_event.h>

int fixup_exception(struct pt_regs *regs)
{
        const struct exception_table_entry *fixup;

        fixup = search_exception_tables(instruction_pointer(regs));
        if (fixup) {
                regs->pc = fixup->fixup;

                return 1;
        }

        return 0;
}

static inline bool is_write(struct pt_regs *regs)
{
        switch (trap_no(regs)) {
        case VEC_TLBINVALIDS:
                return true;
        case VEC_TLBMODIFIED:
                return true;
        }

        return false;
}

#ifdef CONFIG_CPU_HAS_LDSTEX
static inline void csky_cmpxchg_fixup(struct pt_regs *regs)
{
        return;
}
#else
extern unsigned long csky_cmpxchg_ldw;
extern unsigned long csky_cmpxchg_stw;
static inline void csky_cmpxchg_fixup(struct pt_regs *regs)
{
        if (trap_no(regs) != VEC_TLBMODIFIED)
                return;

        if (instruction_pointer(regs) == csky_cmpxchg_stw)
                instruction_pointer_set(regs, csky_cmpxchg_ldw);
        return;
}
#endif

static inline void no_context(struct pt_regs *regs, unsigned long addr)
{
        current->thread.trap_no = trap_no(regs);

        /* Are we prepared to handle this kernel fault? */
        if (fixup_exception(regs))
                return;

        /*
         * Oops. The kernel tried to access some bad page. We'll have to
         * terminate things with extreme prejudice.
         */
        bust_spinlocks(1);
        pr_alert("Unable to handle kernel paging request at virtual "
                 "addr 0x%08lx, pc: 0x%08lx\n", addr, regs->pc);
        die(regs, "Oops");
        do_exit(SIGKILL);
}

static inline void mm_fault_error(struct pt_regs *regs, unsigned long addr, vm_fault_t fault)
{
        current->thread.trap_no = trap_no(regs);

        if (fault & VM_FAULT_OOM) {
                /*
                 * We ran out of memory, call the OOM killer, and return the userspace
                 * (which will retry the fault, or kill us if we got oom-killed).
                 */
                if (!user_mode(regs)) {
                        no_context(regs, addr);
                        return;
                }
                pagefault_out_of_memory();
                return;
        } else if (fault & VM_FAULT_SIGBUS) {
                /* Kernel mode? Handle exceptions or die */
                if (!user_mode(regs)) {
                        no_context(regs, addr);
                        return;
                }
                do_trap(regs, SIGBUS, BUS_ADRERR, addr);
                return;
        }
        BUG();
}

static inline void bad_area(struct pt_regs *regs, struct mm_struct *mm, int code, unsigned long addr)
{
        /*
         * Something tried to access memory that isn't in our memory map.
         * Fix it, but check if it's kernel or user first.
         */
        mmap_read_unlock(mm);
        /* User mode accesses just cause a SIGSEGV */
        if (user_mode(regs)) {
                do_trap(regs, SIGSEGV, code, addr);
                return;
        }

        no_context(regs, addr);
}

static inline void vmalloc_fault(struct pt_regs *regs, int code, unsigned long addr)
{
        pgd_t *pgd, *pgd_k;
        pud_t *pud, *pud_k;
        pmd_t *pmd, *pmd_k;
        pte_t *pte_k;
        int offset;

        /* User mode accesses just cause a SIGSEGV */
        if (user_mode(regs)) {
                do_trap(regs, SIGSEGV, code, addr);
                return;
        }

        /*
         * Synchronize this task's top level page-table
         * with the 'reference' page table.
         *
         * Do _not_ use "tsk" here. We might be inside
         * an interrupt in the middle of a task switch..
         */
        offset = pgd_index(addr);

        pgd = get_pgd() + offset;
        pgd_k = init_mm.pgd + offset;

        if (!pgd_present(*pgd_k)) {
                no_context(regs, addr);
                return;
        }
        set_pgd(pgd, *pgd_k);

        pud = (pud_t *)pgd;
        pud_k = (pud_t *)pgd_k;
        if (!pud_present(*pud_k)) {
                no_context(regs, addr);
                return;
        }

        pmd = pmd_offset(pud, addr);
        pmd_k = pmd_offset(pud_k, addr);
        if (!pmd_present(*pmd_k)) {
                no_context(regs, addr);
                return;
        }
        set_pmd(pmd, *pmd_k);

        pte_k = pte_offset_kernel(pmd_k, addr);
        if (!pte_present(*pte_k)) {
                no_context(regs, addr);
                return;
        }

        flush_tlb_one(addr);
}

static inline bool access_error(struct pt_regs *regs, struct vm_area_struct *vma)
{
        if (is_write(regs)) {
                if (!(vma->vm_flags & VM_WRITE))
                        return true;
        } else {
                if (unlikely(!vma_is_accessible(vma)))
                        return true;
        }
        return false;
}

/*
 * This routine handles page faults.  It determines the address and the
 * problem, and then passes it off to one of the appropriate routines.
 */
asmlinkage void do_page_fault(struct pt_regs *regs)
{
        struct task_struct *tsk;
        struct vm_area_struct *vma;
        struct mm_struct *mm;
        unsigned long addr = read_mmu_entryhi() & PAGE_MASK;
        unsigned int flags = FAULT_FLAG_DEFAULT;
        int code = SEGV_MAPERR;
        vm_fault_t fault;

        tsk = current;
        mm = tsk->mm;

        csky_cmpxchg_fixup(regs);

        if (kprobe_page_fault(regs, tsk->thread.trap_no))
                return;

        /*
         * Fault-in kernel-space virtual memory on-demand.
         * The 'reference' page table is init_mm.pgd.
         *
         * NOTE! We MUST NOT take any locks for this case. We may
         * be in an interrupt or a critical region, and should
         * only copy the information from the master page table,
         * nothing more.
         */
        if (unlikely((addr >= VMALLOC_START) && (addr <= VMALLOC_END))) {
                vmalloc_fault(regs, code, addr);
                return;
        }

        /* Enable interrupts if they were enabled in the parent context. */
        if (likely(regs->sr & BIT(6)))
                local_irq_enable();

        /*
         * If we're in an interrupt, have no user context, or are running
         * in an atomic region, then we must not take the fault.
         */
        if (unlikely(faulthandler_disabled() || !mm)) {
                no_context(regs, addr);
                return;
        }

        if (user_mode(regs))
                flags |= FAULT_FLAG_USER;

        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);

        if (is_write(regs))
                flags |= FAULT_FLAG_WRITE;
retry:
        mmap_read_lock(mm);
        vma = find_vma(mm, addr);
        if (unlikely(!vma)) {
                bad_area(regs, mm, code, addr);
                return;
        }
        if (likely(vma->vm_start <= addr))
                goto good_area;
        if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) {
                bad_area(regs, mm, code, addr);
                return;
        }
        if (unlikely(expand_stack(vma, addr))) {
                bad_area(regs, mm, code, addr);
                return;
        }

        /*
         * Ok, we have a good vm_area for this memory access, so
         * we can handle it.
         */
good_area:
        code = SEGV_ACCERR;

        if (unlikely(access_error(regs, vma))) {
                bad_area(regs, mm, code, addr);
                return;
        }

        /*
         * If for any reason at all we could not handle the fault,
         * make sure we exit gracefully rather than endlessly redo
         * the fault.
         */
        fault = handle_mm_fault(vma, addr, flags, regs);

        /*
         * If we need to retry but a fatal signal is pending, handle the
         * signal first. We do not need to release the mmap_lock because it
         * would already be released in __lock_page_or_retry in mm/filemap.c.
         */
        if (fault_signal_pending(fault, regs)) {
                if (!user_mode(regs))
                        no_context(regs, addr);
                return;
        }

        if (unlikely((fault & VM_FAULT_RETRY) && (flags & FAULT_FLAG_ALLOW_RETRY))) {
                flags |= FAULT_FLAG_TRIED;

                /*
                 * No need to mmap_read_unlock(mm) as we would
                 * have already released it in __lock_page_or_retry
                 * in mm/filemap.c.
                 */
                goto retry;
        }

        mmap_read_unlock(mm);

        if (unlikely(fault & VM_FAULT_ERROR)) {
                mm_fault_error(regs, addr, fault);
                return;
        }
        return;
}