/*
 * Copyright 2014 IBM Corp.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/workqueue.h>
#include <linux/sched.h>
#include <linux/pid.h>
#include <linux/mm.h>
#include <linux/moduleparam.h>

#undef MODULE_PARAM_PREFIX
#define MODULE_PARAM_PREFIX "cxl" "."
#include <asm/current.h>
#include <asm/copro.h>
#include <asm/mmu.h>

#include "cxl.h"
#include "trace.h"

static bool sste_matches(struct cxl_sste *sste, struct copro_slb *slb)
{
        return ((sste->vsid_data == cpu_to_be64(slb->vsid)) &&
                (sste->esid_data == cpu_to_be64(slb->esid)));
}

/*
 * This finds a free SSTE for the given SLB, or returns NULL if it's already in
 * the segment table.
 */
static struct cxl_sste* find_free_sste(struct cxl_context *ctx,
                                       struct copro_slb *slb)
{
        struct cxl_sste *primary, *sste, *ret = NULL;
        unsigned int mask = (ctx->sst_size >> 7) - 1; /* SSTP0[SegTableSize] */
        unsigned int entry;
        unsigned int hash;

        if (slb->vsid & SLB_VSID_B_1T)
                hash = (slb->esid >> SID_SHIFT_1T) & mask;
        else /* 256M */
                hash = (slb->esid >> SID_SHIFT) & mask;

        primary = ctx->sstp + (hash << 3);

        for (entry = 0, sste = primary; entry < 8; entry++, sste++) {
                if (!ret && !(be64_to_cpu(sste->esid_data) & SLB_ESID_V))
                        ret = sste;
                if (sste_matches(sste, slb))
                        return NULL;
        }
        if (ret)
                return ret;

        /* Nothing free, select an entry to cast out */
        ret = primary + ctx->sst_lru;
        ctx->sst_lru = (ctx->sst_lru + 1) & 0x7;

        return ret;
}

static void cxl_load_segment(struct cxl_context *ctx, struct copro_slb *slb)
{
        /* mask is the group index, we search primary and secondary here. */
        struct cxl_sste *sste;
        unsigned long flags;

        spin_lock_irqsave(&ctx->sste_lock, flags);
        sste = find_free_sste(ctx, slb);
        if (!sste)
                goto out_unlock;

        pr_devel("CXL Populating SST[%li]: %#llx %#llx\n",
                        sste - ctx->sstp, slb->vsid, slb->esid);
        trace_cxl_ste_write(ctx, sste - ctx->sstp, slb->esid, slb->vsid);

        sste->vsid_data = cpu_to_be64(slb->vsid);
        sste->esid_data = cpu_to_be64(slb->esid);
out_unlock:
        spin_unlock_irqrestore(&ctx->sste_lock, flags);
}

static int cxl_fault_segment(struct cxl_context *ctx, struct mm_struct *mm,
                             u64 ea)
{
        struct copro_slb slb = {0,0};
        int rc;

        if (!(rc = copro_calculate_slb(mm, ea, &slb))) {
                cxl_load_segment(ctx, &slb);
        }

        return rc;
}

static void cxl_ack_ae(struct cxl_context *ctx)
{
        unsigned long flags;

        cxl_ops->ack_irq(ctx, CXL_PSL_TFC_An_AE, 0);

        spin_lock_irqsave(&ctx->lock, flags);
        ctx->pending_fault = true;
        ctx->fault_addr = ctx->dar;
        ctx->fault_dsisr = ctx->dsisr;
        spin_unlock_irqrestore(&ctx->lock, flags);

        wake_up_all(&ctx->wq);
}

static int cxl_handle_segment_miss(struct cxl_context *ctx,
                                   struct mm_struct *mm, u64 ea)
{
        int rc;

        pr_devel("CXL interrupt: Segment fault pe: %i ea: %#llx\n", ctx->pe, ea);
        trace_cxl_ste_miss(ctx, ea);

        if ((rc = cxl_fault_segment(ctx, mm, ea)))
                cxl_ack_ae(ctx);
        else {

                mb(); /* Order seg table write to TFC MMIO write */
                cxl_ops->ack_irq(ctx, CXL_PSL_TFC_An_R, 0);
        }

        return IRQ_HANDLED;
}

static void cxl_handle_page_fault(struct cxl_context *ctx,
                                  struct mm_struct *mm, u64 dsisr, u64 dar)
{
        unsigned flt = 0;
        int result;
        unsigned long access, flags, inv_flags = 0;

        trace_cxl_pte_miss(ctx, dsisr, dar);

        if ((result = copro_handle_mm_fault(mm, dar, dsisr, &flt))) {
                pr_devel("copro_handle_mm_fault failed: %#x\n", result);
                return cxl_ack_ae(ctx);
        }

        /*
         * update_mmu_cache() will not have loaded the hash since current->trap
         * is not a 0x400 or 0x300, so just call hash_page_mm() here.
         */
        access = _PAGE_PRESENT;
        if (dsisr & CXL_PSL_DSISR_An_S)
                access |= _PAGE_RW;
        if ((!ctx->kernel) || ~(dar & (1ULL << 63)))
                access |= _PAGE_USER;

        if (dsisr & DSISR_NOHPTE)
                inv_flags |= HPTE_NOHPTE_UPDATE;

        local_irq_save(flags);
        hash_page_mm(mm, dar, access, 0x300, inv_flags);
        local_irq_restore(flags);

        pr_devel("Page fault successfully handled for pe: %i!\n", ctx->pe);
        cxl_ops->ack_irq(ctx, CXL_PSL_TFC_An_R, 0);
}

/*
 * Returns the mm_struct corresponding to the context ctx via ctx->pid
 * In case the task has exited we use the task group leader accessible
 * via ctx->glpid to find the next task in the thread group that has a
 * valid  mm_struct associated with it. If a task with valid mm_struct
 * is found the ctx->pid is updated to use the task struct for subsequent
 * translations. In case no valid mm_struct is found in the task group to
 * service the fault a NULL is returned.
 */
static struct mm_struct *get_mem_context(struct cxl_context *ctx)
{
        struct task_struct *task = NULL;
        struct mm_struct *mm = NULL;
        struct pid *old_pid = ctx->pid;

        if (old_pid == NULL) {
                pr_warn("%s: Invalid context for pe=%d\n",
                         __func__, ctx->pe);
                return NULL;
        }

        task = get_pid_task(old_pid, PIDTYPE_PID);

        /*
         * pid_alive may look racy but this saves us from costly
         * get_task_mm when the task is a zombie. In worst case
         * we may think a task is alive, which is about to die
         * but get_task_mm will return NULL.
         */
        if (task != NULL && pid_alive(task))
                mm = get_task_mm(task);

        /* release the task struct that was taken earlier */
        if (task)
                put_task_struct(task);
        else
                pr_devel("%s: Context owning pid=%i for pe=%i dead\n",
                        __func__, pid_nr(old_pid), ctx->pe);

        /*
         * If we couldn't find the mm context then use the group
         * leader to iterate over the task group and find a task
         * that gives us mm_struct.
         */
        if (unlikely(mm == NULL && ctx->glpid != NULL)) {

                rcu_read_lock();
                task = pid_task(ctx->glpid, PIDTYPE_PID);
                if (task)
                        do {
                                mm = get_task_mm(task);
                                if (mm) {
                                        ctx->pid = get_task_pid(task,
                                                                PIDTYPE_PID);
                                        break;
                                }
                                task = next_thread(task);
                        } while (task && !thread_group_leader(task));
                rcu_read_unlock();

                /* check if we switched pid */
                if (ctx->pid != old_pid) {
                        if (mm)
                                pr_devel("%s:pe=%i switch pid %i->%i\n",
                                         __func__, ctx->pe, pid_nr(old_pid),
                                         pid_nr(ctx->pid));
                        else
                                pr_devel("%s:Cannot find mm for pid=%i\n",
                                         __func__, pid_nr(old_pid));

                        /* drop the reference to older pid */
                        put_pid(old_pid);
                }
        }

        return mm;
}



void cxl_handle_fault(struct work_struct *fault_work)
{
        struct cxl_context *ctx =
                container_of(fault_work, struct cxl_context, fault_work);
        u64 dsisr = ctx->dsisr;
        u64 dar = ctx->dar;
        struct mm_struct *mm = NULL;

        if (cpu_has_feature(CPU_FTR_HVMODE)) {
                if (cxl_p2n_read(ctx->afu, CXL_PSL_DSISR_An) != dsisr ||
                    cxl_p2n_read(ctx->afu, CXL_PSL_DAR_An) != dar ||
                    cxl_p2n_read(ctx->afu, CXL_PSL_PEHandle_An) != ctx->pe) {
                        /* Most likely explanation is harmless - a dedicated
                         * process has detached and these were cleared by the
                         * PSL purge, but warn about it just in case
                         */
                        dev_notice(&ctx->afu->dev, "cxl_handle_fault: Translation fault regs changed\n");
                        return;
                }
        }

        /* Early return if the context is being / has been detached */
        if (ctx->status == CLOSED) {
                cxl_ack_ae(ctx);
                return;
        }

        pr_devel("CXL BOTTOM HALF handling fault for afu pe: %i. "
                "DSISR: %#llx DAR: %#llx\n", ctx->pe, dsisr, dar);

        if (!ctx->kernel) {

                mm = get_mem_context(ctx);
                /* indicates all the thread in task group have exited */
                if (mm == NULL) {
                        pr_devel("%s: unable to get mm for pe=%d pid=%i\n",
                                 __func__, ctx->pe, pid_nr(ctx->pid));
                        cxl_ack_ae(ctx);
                        return;
                } else {
                        pr_devel("Handling page fault for pe=%d pid=%i\n",
                                 ctx->pe, pid_nr(ctx->pid));
                }
        }

        if (dsisr & CXL_PSL_DSISR_An_DS)
                cxl_handle_segment_miss(ctx, mm, dar);
        else if (dsisr & CXL_PSL_DSISR_An_DM)
                cxl_handle_page_fault(ctx, mm, dsisr, dar);
        else
                WARN(1, "cxl_handle_fault has nothing to handle\n");

        if (mm)
                mmput(mm);
}

static void cxl_prefault_one(struct cxl_context *ctx, u64 ea)
{
        struct mm_struct *mm;

        mm = get_mem_context(ctx);
        if (mm == NULL) {
                pr_devel("cxl_prefault_one unable to get mm %i\n",
                         pid_nr(ctx->pid));
                return;
        }

        cxl_fault_segment(ctx, mm, ea);

        mmput(mm);
}

static u64 next_segment(u64 ea, u64 vsid)
{
        if (vsid & SLB_VSID_B_1T)
                ea |= (1ULL << 40) - 1;
        else
                ea |= (1ULL << 28) - 1;

        return ea + 1;
}

static void cxl_prefault_vma(struct cxl_context *ctx)
{
        u64 ea, last_esid = 0;
        struct copro_slb slb;
        struct vm_area_struct *vma;
        int rc;
        struct mm_struct *mm;

        mm = get_mem_context(ctx);
        if (mm == NULL) {
                pr_devel("cxl_prefault_vm unable to get mm %i\n",
                         pid_nr(ctx->pid));
                return;
        }

        down_read(&mm->mmap_sem);
        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                for (ea = vma->vm_start; ea < vma->vm_end;
                                ea = next_segment(ea, slb.vsid)) {
                        rc = copro_calculate_slb(mm, ea, &slb);
                        if (rc)
                                continue;

                        if (last_esid == slb.esid)
                                continue;

                        cxl_load_segment(ctx, &slb);
                        last_esid = slb.esid;
                }
        }
        up_read(&mm->mmap_sem);

        mmput(mm);
}

void cxl_prefault(struct cxl_context *ctx, u64 wed)
{
        switch (ctx->afu->prefault_mode) {
        case CXL_PREFAULT_WED:
                cxl_prefault_one(ctx, wed);
                break;
        case CXL_PREFAULT_ALL:
                cxl_prefault_vma(ctx);
                break;
        default:
                break;
        }
}