sgi-gru: support multiple pagesizes in GRU

[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / drivers / misc / sgi-gru / grumain.c

/*
 * SN Platform GRU Driver
 *
 *            DRIVER TABLE MANAGER + GRU CONTEXT LOAD/UNLOAD
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Copyright (c) 2008 Silicon Graphics, Inc.  All Rights Reserved.
 */

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/mm.h>
#include <linux/spinlock.h>
#include <linux/sched.h>
#include <linux/device.h>
#include <linux/list.h>
#include <asm/uv/uv_hub.h>
#include "gru.h"
#include "grutables.h"
#include "gruhandles.h"

unsigned long gru_options __read_mostly;

static struct device_driver gru_driver = {
        .name = "gru"
};

static struct device gru_device = {
        .init_name = "",
        .driver = &gru_driver,
};

struct device *grudev = &gru_device;

/*
 * Select a gru fault map to be used by the current cpu. Note that
 * multiple cpus may be using the same map.
 *      ZZZ should "shift" be used?? Depends on HT cpu numbering
 *      ZZZ should be inline but did not work on emulator
 */
int gru_cpu_fault_map_id(void)
{
        return uv_blade_processor_id() % GRU_NUM_TFM;
}

/*--------- ASID Management -------------------------------------------
 *
 *  Initially, assign asids sequentially from MIN_ASID .. MAX_ASID.
 *  Once MAX is reached, flush the TLB & start over. However,
 *  some asids may still be in use. There won't be many (percentage wise) still
 *  in use. Search active contexts & determine the value of the first
 *  asid in use ("x"s below). Set "limit" to this value.
 *  This defines a block of assignable asids.
 *
 *  When "limit" is reached, search forward from limit+1 and determine the
 *  next block of assignable asids.
 *
 *  Repeat until MAX_ASID is reached, then start over again.
 *
 *  Each time MAX_ASID is reached, increment the asid generation. Since
 *  the search for in-use asids only checks contexts with GRUs currently
 *  assigned, asids in some contexts will be missed. Prior to loading
 *  a context, the asid generation of the GTS asid is rechecked. If it
 *  doesn't match the current generation, a new asid will be assigned.
 *
 *      0---------------x------------x---------------------x----|
 *        ^-next        ^-limit                                 ^-MAX_ASID
 *
 * All asid manipulation & context loading/unloading is protected by the
 * gs_lock.
 */

/* Hit the asid limit. Start over */
static int gru_wrap_asid(struct gru_state *gru)
{
        gru_dbg(grudev, "gid %d\n", gru->gs_gid);
        STAT(asid_wrap);
        gru->gs_asid_gen++;
        return MIN_ASID;
}

/* Find the next chunk of unused asids */
static int gru_reset_asid_limit(struct gru_state *gru, int asid)
{
        int i, gid, inuse_asid, limit;

        gru_dbg(grudev, "gid %d, asid 0x%x\n", gru->gs_gid, asid);
        STAT(asid_next);
        limit = MAX_ASID;
        if (asid >= limit)
                asid = gru_wrap_asid(gru);
        gru_flush_all_tlb(gru);
        gid = gru->gs_gid;
again:
        for (i = 0; i < GRU_NUM_CCH; i++) {
                if (!gru->gs_gts[i])
                        continue;
                inuse_asid = gru->gs_gts[i]->ts_gms->ms_asids[gid].mt_asid;
                gru_dbg(grudev, "gid %d, gts %p, gms %p, inuse 0x%x, cxt %d\n",
                        gru->gs_gid, gru->gs_gts[i], gru->gs_gts[i]->ts_gms,
                        inuse_asid, i);
                if (inuse_asid == asid) {
                        asid += ASID_INC;
                        if (asid >= limit) {
                                /*
                                 * empty range: reset the range limit and
                                 * start over
                                 */
                                limit = MAX_ASID;
                                if (asid >= MAX_ASID)
                                        asid = gru_wrap_asid(gru);
                                goto again;
                        }
                }

                if ((inuse_asid > asid) && (inuse_asid < limit))
                        limit = inuse_asid;
        }
        gru->gs_asid_limit = limit;
        gru->gs_asid = asid;
        gru_dbg(grudev, "gid %d, new asid 0x%x, new_limit 0x%x\n", gru->gs_gid,
                                        asid, limit);
        return asid;
}

/* Assign a new ASID to a thread context.  */
static int gru_assign_asid(struct gru_state *gru)
{
        int asid;

        gru->gs_asid += ASID_INC;
        asid = gru->gs_asid;
        if (asid >= gru->gs_asid_limit)
                asid = gru_reset_asid_limit(gru, asid);

        gru_dbg(grudev, "gid %d, asid 0x%x\n", gru->gs_gid, asid);
        return asid;
}

/*
 * Clear n bits in a word. Return a word indicating the bits that were cleared.
 * Optionally, build an array of chars that contain the bit numbers allocated.
 */
static unsigned long reserve_resources(unsigned long *p, int n, int mmax,
                                       char *idx)
{
        unsigned long bits = 0;
        int i;

        do {
                i = find_first_bit(p, mmax);
                if (i == mmax)
                        BUG();
                __clear_bit(i, p);
                __set_bit(i, &bits);
                if (idx)
                        *idx++ = i;
        } while (--n);
        return bits;
}

unsigned long gru_reserve_cb_resources(struct gru_state *gru, int cbr_au_count,
                                       char *cbmap)
{
        return reserve_resources(&gru->gs_cbr_map, cbr_au_count, GRU_CBR_AU,
                                 cbmap);
}

unsigned long gru_reserve_ds_resources(struct gru_state *gru, int dsr_au_count,
                                       char *dsmap)
{
        return reserve_resources(&gru->gs_dsr_map, dsr_au_count, GRU_DSR_AU,
                                 dsmap);
}

static void reserve_gru_resources(struct gru_state *gru,
                                  struct gru_thread_state *gts)
{
        gru->gs_active_contexts++;
        gts->ts_cbr_map =
            gru_reserve_cb_resources(gru, gts->ts_cbr_au_count,
                                     gts->ts_cbr_idx);
        gts->ts_dsr_map =
            gru_reserve_ds_resources(gru, gts->ts_dsr_au_count, NULL);
}

static void free_gru_resources(struct gru_state *gru,
                               struct gru_thread_state *gts)
{
        gru->gs_active_contexts--;
        gru->gs_cbr_map |= gts->ts_cbr_map;
        gru->gs_dsr_map |= gts->ts_dsr_map;
}

/*
 * Check if a GRU has sufficient free resources to satisfy an allocation
 * request. Note: GRU locks may or may not be held when this is called. If
 * not held, recheck after acquiring the appropriate locks.
 *
 * Returns 1 if sufficient resources, 0 if not
 */
static int check_gru_resources(struct gru_state *gru, int cbr_au_count,
                               int dsr_au_count, int max_active_contexts)
{
        return hweight64(gru->gs_cbr_map) >= cbr_au_count
                && hweight64(gru->gs_dsr_map) >= dsr_au_count
                && gru->gs_active_contexts < max_active_contexts;
}

/*
 * TLB manangment requires tracking all GRU chiplets that have loaded a GSEG
 * context.
 */
static int gru_load_mm_tracker(struct gru_state *gru,
                                        struct gru_thread_state *gts)
{
        struct gru_mm_struct *gms = gts->ts_gms;
        struct gru_mm_tracker *asids = &gms->ms_asids[gru->gs_gid];
        unsigned short ctxbitmap = (1 << gts->ts_ctxnum);
        int asid;

        spin_lock(&gms->ms_asid_lock);
        asid = asids->mt_asid;

        spin_lock(&gru->gs_asid_lock);
        if (asid == 0 || (asids->mt_ctxbitmap == 0 && asids->mt_asid_gen !=
                          gru->gs_asid_gen)) {
                asid = gru_assign_asid(gru);
                asids->mt_asid = asid;
                asids->mt_asid_gen = gru->gs_asid_gen;
                STAT(asid_new);
        } else {
                STAT(asid_reuse);
        }
        spin_unlock(&gru->gs_asid_lock);

        BUG_ON(asids->mt_ctxbitmap & ctxbitmap);
        asids->mt_ctxbitmap |= ctxbitmap;
        if (!test_bit(gru->gs_gid, gms->ms_asidmap))
                __set_bit(gru->gs_gid, gms->ms_asidmap);
        spin_unlock(&gms->ms_asid_lock);

        gru_dbg(grudev,
                "gid %d, gts %p, gms %p, ctxnum %d, asid 0x%x, asidmap 0x%lx\n",
                gru->gs_gid, gts, gms, gts->ts_ctxnum, asid,
                gms->ms_asidmap[0]);
        return asid;
}

static void gru_unload_mm_tracker(struct gru_state *gru,
                                        struct gru_thread_state *gts)
{
        struct gru_mm_struct *gms = gts->ts_gms;
        struct gru_mm_tracker *asids;
        unsigned short ctxbitmap;

        asids = &gms->ms_asids[gru->gs_gid];
        ctxbitmap = (1 << gts->ts_ctxnum);
        spin_lock(&gms->ms_asid_lock);
        spin_lock(&gru->gs_asid_lock);
        BUG_ON((asids->mt_ctxbitmap & ctxbitmap) != ctxbitmap);
        asids->mt_ctxbitmap ^= ctxbitmap;
        gru_dbg(grudev, "gid %d, gts %p, gms %p, ctxnum 0x%d, asidmap 0x%lx\n",
                gru->gs_gid, gts, gms, gts->ts_ctxnum, gms->ms_asidmap[0]);
        spin_unlock(&gru->gs_asid_lock);
        spin_unlock(&gms->ms_asid_lock);
}

/*
 * Decrement the reference count on a GTS structure. Free the structure
 * if the reference count goes to zero.
 */
void gts_drop(struct gru_thread_state *gts)
{
        if (gts && atomic_dec_return(&gts->ts_refcnt) == 0) {
                gru_drop_mmu_notifier(gts->ts_gms);
                kfree(gts);
                STAT(gts_free);
        }
}

/*
 * Locate the GTS structure for the current thread.
 */
static struct gru_thread_state *gru_find_current_gts_nolock(struct gru_vma_data
                            *vdata, int tsid)
{
        struct gru_thread_state *gts;

        list_for_each_entry(gts, &vdata->vd_head, ts_next)
            if (gts->ts_tsid == tsid)
                return gts;
        return NULL;
}

/*
 * Allocate a thread state structure.
 */
static struct gru_thread_state *gru_alloc_gts(struct vm_area_struct *vma,
                                              struct gru_vma_data *vdata,
                                              int tsid)
{
        struct gru_thread_state *gts;
        int bytes;

        bytes = DSR_BYTES(vdata->vd_dsr_au_count) +
                                CBR_BYTES(vdata->vd_cbr_au_count);
        bytes += sizeof(struct gru_thread_state);
        gts = kzalloc(bytes, GFP_KERNEL);
        if (!gts)
                return NULL;

        STAT(gts_alloc);
        atomic_set(&gts->ts_refcnt, 1);
        mutex_init(&gts->ts_ctxlock);
        gts->ts_cbr_au_count = vdata->vd_cbr_au_count;
        gts->ts_dsr_au_count = vdata->vd_dsr_au_count;
        gts->ts_user_options = vdata->vd_user_options;
        gts->ts_tsid = tsid;
        gts->ts_user_options = vdata->vd_user_options;
        gts->ts_ctxnum = NULLCTX;
        gts->ts_mm = current->mm;
        gts->ts_vma = vma;
        gts->ts_tlb_int_select = -1;
        gts->ts_gms = gru_register_mmu_notifier();
        gts->ts_sizeavail = GRU_SIZEAVAIL(PAGE_SHIFT);
        if (!gts->ts_gms)
                goto err;

        gru_dbg(grudev, "alloc vdata %p, new gts %p\n", vdata, gts);
        return gts;

err:
        gts_drop(gts);
        return NULL;
}

/*
 * Allocate a vma private data structure.
 */
struct gru_vma_data *gru_alloc_vma_data(struct vm_area_struct *vma, int tsid)
{
        struct gru_vma_data *vdata = NULL;

        vdata = kmalloc(sizeof(*vdata), GFP_KERNEL);
        if (!vdata)
                return NULL;

        INIT_LIST_HEAD(&vdata->vd_head);
        spin_lock_init(&vdata->vd_lock);
        gru_dbg(grudev, "alloc vdata %p\n", vdata);
        return vdata;
}

/*
 * Find the thread state structure for the current thread.
 */
struct gru_thread_state *gru_find_thread_state(struct vm_area_struct *vma,
                                        int tsid)
{
        struct gru_vma_data *vdata = vma->vm_private_data;
        struct gru_thread_state *gts;

        spin_lock(&vdata->vd_lock);
        gts = gru_find_current_gts_nolock(vdata, tsid);
        spin_unlock(&vdata->vd_lock);
        gru_dbg(grudev, "vma %p, gts %p\n", vma, gts);
        return gts;
}

/*
 * Allocate a new thread state for a GSEG. Note that races may allow
 * another thread to race to create a gts.
 */
struct gru_thread_state *gru_alloc_thread_state(struct vm_area_struct *vma,
                                        int tsid)
{
        struct gru_vma_data *vdata = vma->vm_private_data;
        struct gru_thread_state *gts, *ngts;

        gts = gru_alloc_gts(vma, vdata, tsid);
        if (!gts)
                return NULL;

        spin_lock(&vdata->vd_lock);
        ngts = gru_find_current_gts_nolock(vdata, tsid);
        if (ngts) {
                gts_drop(gts);
                gts = ngts;
                STAT(gts_double_allocate);
        } else {
                list_add(&gts->ts_next, &vdata->vd_head);
        }
        spin_unlock(&vdata->vd_lock);
        gru_dbg(grudev, "vma %p, gts %p\n", vma, gts);
        return gts;
}

/*
 * Free the GRU context assigned to the thread state.
 */
static void gru_free_gru_context(struct gru_thread_state *gts)
{
        struct gru_state *gru;

        gru = gts->ts_gru;
        gru_dbg(grudev, "gts %p, gid %d\n", gts, gru->gs_gid);

        spin_lock(&gru->gs_lock);
        gru->gs_gts[gts->ts_ctxnum] = NULL;
        free_gru_resources(gru, gts);
        BUG_ON(test_bit(gts->ts_ctxnum, &gru->gs_context_map) == 0);
        __clear_bit(gts->ts_ctxnum, &gru->gs_context_map);
        gts->ts_ctxnum = NULLCTX;
        gts->ts_gru = NULL;
        gts->ts_blade = -1;
        spin_unlock(&gru->gs_lock);

        gts_drop(gts);
        STAT(free_context);
}

/*
 * Prefetching cachelines help hardware performance.
 * (Strictly a performance enhancement. Not functionally required).
 */
static void prefetch_data(void *p, int num, int stride)
{
        while (num-- > 0) {
                prefetchw(p);
                p += stride;
        }
}

static inline long gru_copy_handle(void *d, void *s)
{
        memcpy(d, s, GRU_HANDLE_BYTES);
        return GRU_HANDLE_BYTES;
}

static void gru_prefetch_context(void *gseg, void *cb, void *cbe,
                                unsigned long cbrmap, unsigned long length)
{
        int i, scr;

        prefetch_data(gseg + GRU_DS_BASE, length / GRU_CACHE_LINE_BYTES,
                      GRU_CACHE_LINE_BYTES);

        for_each_cbr_in_allocation_map(i, &cbrmap, scr) {
                prefetch_data(cb, 1, GRU_CACHE_LINE_BYTES);
                prefetch_data(cbe + i * GRU_HANDLE_STRIDE, 1,
                              GRU_CACHE_LINE_BYTES);
                cb += GRU_HANDLE_STRIDE;
        }
}

static void gru_load_context_data(void *save, void *grubase, int ctxnum,
                                  unsigned long cbrmap, unsigned long dsrmap)
{
        void *gseg, *cb, *cbe;
        unsigned long length;
        int i, scr;

        gseg = grubase + ctxnum * GRU_GSEG_STRIDE;
        cb = gseg + GRU_CB_BASE;
        cbe = grubase + GRU_CBE_BASE;
        length = hweight64(dsrmap) * GRU_DSR_AU_BYTES;
        gru_prefetch_context(gseg, cb, cbe, cbrmap, length);

        for_each_cbr_in_allocation_map(i, &cbrmap, scr) {
                save += gru_copy_handle(cb, save);
                save += gru_copy_handle(cbe + i * GRU_HANDLE_STRIDE, save);
                cb += GRU_HANDLE_STRIDE;
        }

        memcpy(gseg + GRU_DS_BASE, save, length);
}

static void gru_unload_context_data(void *save, void *grubase, int ctxnum,
                                    unsigned long cbrmap, unsigned long dsrmap)
{
        void *gseg, *cb, *cbe;
        unsigned long length;
        int i, scr;

        gseg = grubase + ctxnum * GRU_GSEG_STRIDE;
        cb = gseg + GRU_CB_BASE;
        cbe = grubase + GRU_CBE_BASE;
        length = hweight64(dsrmap) * GRU_DSR_AU_BYTES;
        gru_prefetch_context(gseg, cb, cbe, cbrmap, length);

        for_each_cbr_in_allocation_map(i, &cbrmap, scr) {
                save += gru_copy_handle(save, cb);
                save += gru_copy_handle(save, cbe + i * GRU_HANDLE_STRIDE);
                cb += GRU_HANDLE_STRIDE;
        }
        memcpy(save, gseg + GRU_DS_BASE, length);
}

void gru_unload_context(struct gru_thread_state *gts, int savestate)
{
        struct gru_state *gru = gts->ts_gru;
        struct gru_context_configuration_handle *cch;
        int ctxnum = gts->ts_ctxnum;

        zap_vma_ptes(gts->ts_vma, UGRUADDR(gts), GRU_GSEG_PAGESIZE);
        cch = get_cch(gru->gs_gru_base_vaddr, ctxnum);

        gru_dbg(grudev, "gts %p\n", gts);
        lock_cch_handle(cch);
        if (cch_interrupt_sync(cch))
                BUG();

        gru_unload_mm_tracker(gru, gts);
        if (savestate)
                gru_unload_context_data(gts->ts_gdata, gru->gs_gru_base_vaddr,
                                        ctxnum, gts->ts_cbr_map,
                                        gts->ts_dsr_map);

        if (cch_deallocate(cch))
                BUG();
        gts->ts_force_unload = 0;       /* ts_force_unload locked by CCH lock */
        unlock_cch_handle(cch);

        gru_free_gru_context(gts);
        STAT(unload_context);
}

/*
 * Load a GRU context by copying it from the thread data structure in memory
 * to the GRU.
 */
static void gru_load_context(struct gru_thread_state *gts)
{
        struct gru_state *gru = gts->ts_gru;
        struct gru_context_configuration_handle *cch;
        int err, asid, ctxnum = gts->ts_ctxnum;

        gru_dbg(grudev, "gts %p\n", gts);
        cch = get_cch(gru->gs_gru_base_vaddr, ctxnum);

        lock_cch_handle(cch);
        asid = gru_load_mm_tracker(gru, gts);
        cch->tfm_fault_bit_enable =
            (gts->ts_user_options == GRU_OPT_MISS_FMM_POLL
             || gts->ts_user_options == GRU_OPT_MISS_FMM_INTR);
        cch->tlb_int_enable = (gts->ts_user_options == GRU_OPT_MISS_FMM_INTR);
        if (cch->tlb_int_enable) {
                gts->ts_tlb_int_select = gru_cpu_fault_map_id();
                cch->tlb_int_select = gts->ts_tlb_int_select;
        }
        cch->tfm_done_bit_enable = 0;
        err = cch_allocate(cch, asid, gts->ts_sizeavail, gts->ts_cbr_map,
                                gts->ts_dsr_map);
        if (err) {
                gru_dbg(grudev,
                        "err %d: cch %p, gts %p, cbr 0x%lx, dsr 0x%lx\n",
                        err, cch, gts, gts->ts_cbr_map, gts->ts_dsr_map);
                BUG();
        }

        gru_load_context_data(gts->ts_gdata, gru->gs_gru_base_vaddr, ctxnum,
                              gts->ts_cbr_map, gts->ts_dsr_map);

        if (cch_start(cch))
                BUG();
        unlock_cch_handle(cch);

        STAT(load_context);
}

/*
 * Update fields in an active CCH:
 *      - retarget interrupts on local blade
 *      - update sizeavail mask
 *      - force a delayed context unload by clearing the CCH asids. This
 *        forces TLB misses for new GRU instructions. The context is unloaded
 *        when the next TLB miss occurs.
 */
int gru_update_cch(struct gru_thread_state *gts, int force_unload)
{
        struct gru_context_configuration_handle *cch;
        struct gru_state *gru = gts->ts_gru;
        int i, ctxnum = gts->ts_ctxnum, ret = 0;

        cch = get_cch(gru->gs_gru_base_vaddr, ctxnum);

        lock_cch_handle(cch);
        if (cch->state == CCHSTATE_ACTIVE) {
                if (gru->gs_gts[gts->ts_ctxnum] != gts)
                        goto exit;
                if (cch_interrupt(cch))
                        BUG();
                if (!force_unload) {
                        for (i = 0; i < 8; i++)
                                cch->sizeavail[i] = gts->ts_sizeavail;
                        gts->ts_tlb_int_select = gru_cpu_fault_map_id();
                        cch->tlb_int_select = gru_cpu_fault_map_id();
                } else {
                        for (i = 0; i < 8; i++)
                                cch->asid[i] = 0;
                        cch->tfm_fault_bit_enable = 0;
                        cch->tlb_int_enable = 0;
                        gts->ts_force_unload = 1;
                }
                if (cch_start(cch))
                        BUG();
                ret = 1;
        }
exit:
        unlock_cch_handle(cch);
        return ret;
}

/*
 * Update CCH tlb interrupt select. Required when all the following is true:
 *      - task's GRU context is loaded into a GRU
 *      - task is using interrupt notification for TLB faults
 *      - task has migrated to a different cpu on the same blade where
 *        it was previously running.
 */
static int gru_retarget_intr(struct gru_thread_state *gts)
{
        if (gts->ts_tlb_int_select < 0
            || gts->ts_tlb_int_select == gru_cpu_fault_map_id())
                return 0;

        gru_dbg(grudev, "retarget from %d to %d\n", gts->ts_tlb_int_select,
                gru_cpu_fault_map_id());
        return gru_update_cch(gts, 0);
}


/*
 * Insufficient GRU resources available on the local blade. Steal a context from
 * a process. This is a hack until a _real_ resource scheduler is written....
 */
#define next_ctxnum(n)  ((n) <  GRU_NUM_CCH - 2 ? (n) + 1 : 0)
#define next_gru(b, g)  (((g) < &(b)->bs_grus[GRU_CHIPLETS_PER_BLADE - 1]) ?  \
                                 ((g)+1) : &(b)->bs_grus[0])

static void gru_steal_context(struct gru_thread_state *gts)
{
        struct gru_blade_state *blade;
        struct gru_state *gru, *gru0;
        struct gru_thread_state *ngts = NULL;
        int ctxnum, ctxnum0, flag = 0, cbr, dsr;

        cbr = gts->ts_cbr_au_count;
        dsr = gts->ts_dsr_au_count;

        preempt_disable();
        blade = gru_base[uv_numa_blade_id()];
        spin_lock(&blade->bs_lock);

        ctxnum = next_ctxnum(blade->bs_lru_ctxnum);
        gru = blade->bs_lru_gru;
        if (ctxnum == 0)
                gru = next_gru(blade, gru);
        ctxnum0 = ctxnum;
        gru0 = gru;
        while (1) {
                if (check_gru_resources(gru, cbr, dsr, GRU_NUM_CCH))
                        break;
                spin_lock(&gru->gs_lock);
                for (; ctxnum < GRU_NUM_CCH; ctxnum++) {
                        if (flag && gru == gru0 && ctxnum == ctxnum0)
                                break;
                        ngts = gru->gs_gts[ctxnum];
                        /*
                         * We are grabbing locks out of order, so trylock is
                         * needed. GTSs are usually not locked, so the odds of
                         * success are high. If trylock fails, try to steal a
                         * different GSEG.
                         */
                        if (ngts && mutex_trylock(&ngts->ts_ctxlock))
                                break;
                        ngts = NULL;
                        flag = 1;
                }
                spin_unlock(&gru->gs_lock);
                if (ngts || (flag && gru == gru0 && ctxnum == ctxnum0))
                        break;
                ctxnum = 0;
                gru = next_gru(blade, gru);
        }
        blade->bs_lru_gru = gru;
        blade->bs_lru_ctxnum = ctxnum;
        spin_unlock(&blade->bs_lock);
        preempt_enable();

        if (ngts) {
                STAT(steal_context);
                ngts->ts_steal_jiffies = jiffies;
                gru_unload_context(ngts, 1);
                mutex_unlock(&ngts->ts_ctxlock);
        } else {
                STAT(steal_context_failed);
        }
        gru_dbg(grudev,
                "stole gid %d, ctxnum %d from gts %p. Need cb %d, ds %d;"
                " avail cb %ld, ds %ld\n",
                gru->gs_gid, ctxnum, ngts, cbr, dsr, hweight64(gru->gs_cbr_map),
                hweight64(gru->gs_dsr_map));
}

/*
 * Scan the GRUs on the local blade & assign a GRU context.
 */
static struct gru_state *gru_assign_gru_context(struct gru_thread_state *gts)
{
        struct gru_state *gru, *grux;
        int i, max_active_contexts;

        preempt_disable();

again:
        gru = NULL;
        max_active_contexts = GRU_NUM_CCH;
        for_each_gru_on_blade(grux, uv_numa_blade_id(), i) {
                if (check_gru_resources(grux, gts->ts_cbr_au_count,
                                        gts->ts_dsr_au_count,
                                        max_active_contexts)) {
                        gru = grux;
                        max_active_contexts = grux->gs_active_contexts;
                        if (max_active_contexts == 0)
                                break;
                }
        }

        if (gru) {
                spin_lock(&gru->gs_lock);
                if (!check_gru_resources(gru, gts->ts_cbr_au_count,
                                         gts->ts_dsr_au_count, GRU_NUM_CCH)) {
                        spin_unlock(&gru->gs_lock);
                        goto again;
                }
                reserve_gru_resources(gru, gts);
                gts->ts_gru = gru;
                gts->ts_blade = gru->gs_blade_id;
                gts->ts_ctxnum =
                    find_first_zero_bit(&gru->gs_context_map, GRU_NUM_CCH);
                BUG_ON(gts->ts_ctxnum == GRU_NUM_CCH);
                atomic_inc(&gts->ts_refcnt);
                gru->gs_gts[gts->ts_ctxnum] = gts;
                __set_bit(gts->ts_ctxnum, &gru->gs_context_map);
                spin_unlock(&gru->gs_lock);

                STAT(assign_context);
                gru_dbg(grudev,
                        "gseg %p, gts %p, gid %d, ctx %d, cbr %d, dsr %d\n",
                        gseg_virtual_address(gts->ts_gru, gts->ts_ctxnum), gts,
                        gts->ts_gru->gs_gid, gts->ts_ctxnum,
                        gts->ts_cbr_au_count, gts->ts_dsr_au_count);
        } else {
                gru_dbg(grudev, "failed to allocate a GTS %s\n", "");
                STAT(assign_context_failed);
        }

        preempt_enable();
        return gru;
}

/*
 * gru_nopage
 *
 * Map the user's GRU segment
 *
 *      Note: gru segments alway mmaped on GRU_GSEG_PAGESIZE boundaries.
 */
int gru_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
{
        struct gru_thread_state *gts;
        unsigned long paddr, vaddr;

        vaddr = (unsigned long)vmf->virtual_address;
        gru_dbg(grudev, "vma %p, vaddr 0x%lx (0x%lx)\n",
                vma, vaddr, GSEG_BASE(vaddr));
        STAT(nopfn);

        /* The following check ensures vaddr is a valid address in the VMA */
        gts = gru_find_thread_state(vma, TSID(vaddr, vma));
        if (!gts)
                return VM_FAULT_SIGBUS;

again:
        mutex_lock(&gts->ts_ctxlock);
        preempt_disable();
        if (gts->ts_gru) {
                if (gts->ts_gru->gs_blade_id != uv_numa_blade_id()) {
                        STAT(migrated_nopfn_unload);
                        gru_unload_context(gts, 1);
                } else {
                        if (gru_retarget_intr(gts))
                                STAT(migrated_nopfn_retarget);
                }
        }

        if (!gts->ts_gru) {
                if (!gru_assign_gru_context(gts)) {
                        mutex_unlock(&gts->ts_ctxlock);
                        preempt_enable();
                        schedule_timeout(GRU_ASSIGN_DELAY);  /* true hack ZZZ */
                        if (gts->ts_steal_jiffies + GRU_STEAL_DELAY < jiffies)
                                gru_steal_context(gts);
                        goto again;
                }
                gru_load_context(gts);
                paddr = gseg_physical_address(gts->ts_gru, gts->ts_ctxnum);
                remap_pfn_range(vma, vaddr & ~(GRU_GSEG_PAGESIZE - 1),
                                paddr >> PAGE_SHIFT, GRU_GSEG_PAGESIZE,
                                vma->vm_page_prot);
        }

        mutex_unlock(&gts->ts_ctxlock);
        preempt_enable();

        return VM_FAULT_NOPAGE;
}