ClabureDB: Classified Bug-Reports Database

  /*
   * SN Platform GRU Driver
   *
   *                 MMUOPS callbacks  + TLB flushing
   *
   * This file handles emu notifier callbacks from the core kernel. The callbacks
   * are used to update the TLB in the GRU as a result of changes in the
   * state of a process address space. This file also handles TLB invalidates
   * from the GRU driver.
  *
  *  Copyright (c) 2008 Silicon Graphics, Inc.  All Rights Reserved.
  *
  *  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.
  *
  *  This program is distributed in the hope that it will be useful,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  *  GNU General Public License for more details.
  *
  *  You should have received a copy of the GNU General Public License
  *  along with this program; if not, write to the Free Software
  *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
  */
 
 #include <linux/kernel.h>
 #include <linux/list.h>
 #include <linux/spinlock.h>
 #include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/device.h>
 #include <linux/hugetlb.h>
 #include <linux/delay.h>
 #include <linux/timex.h>
 #include <linux/srcu.h>
 #include <asm/processor.h>
 #include "gru.h"
 #include "grutables.h"
 #include <asm/uv/uv_hub.h>
 
 #define gru_random()        get_cycles()
 
 /* ---------------------------------- TLB Invalidation functions --------
  * get_tgh_handle
  *
  * Find a TGH to use for issuing a TLB invalidate. For GRUs that are on the
  * local blade, use a fixed TGH that is a function of the blade-local cpu
  * number. Normally, this TGH is private to the cpu & no contention occurs for
  * the TGH. For offblade GRUs, select a random TGH in the range above the
  * private TGHs. A spinlock is required to access this TGH & the lock must be
  * released when the invalidate is completes. This sucks, but it is the best we
  * can do.
  *
  * Note that the spinlock is IN the TGH handle so locking does not involve
  * additional cache lines.
  *
  */
 static inline int get_off_blade_tgh(struct gru_state *gru)
 {
         int n;
 
         n = GRU_NUM_TGH - gru->gs_tgh_first_remote;
         n = gru_random() % n;
         n += gru->gs_tgh_first_remote;
         return n;
 }
 
 static inline int get_on_blade_tgh(struct gru_state *gru)
 {
         return uv_blade_processor_id() >> gru->gs_tgh_local_shift;
 }
 
 static struct gru_tlb_global_handle *get_lock_tgh_handle(struct gru_state
                                                          *gru)
 {
         struct gru_tlb_global_handle *tgh;
         int n;
 
         preempt_disable();
         if (uv_numa_blade_id() == gru->gs_blade_id)
                 n = get_on_blade_tgh(gru);
         else
                 n = get_off_blade_tgh(gru);
         tgh = get_tgh_by_index(gru, n);
         lock_tgh_handle(tgh);
 
         return tgh;
 }
 
 static void get_unlock_tgh_handle(struct gru_tlb_global_handle *tgh)
 {
         unlock_tgh_handle(tgh);
         preempt_enable();
 }
 
 /*
  * gru_flush_tlb_range
 *
 * General purpose TLB invalidation function. This function scans every GRU in
 * the ENTIRE system (partition) looking for GRUs where the specified MM has
 * been accessed by the GRU. For each GRU found, the TLB must be invalidated OR
 * the ASID invalidated. Invalidating an ASID causes a new ASID to be assigned
 * on the next fault. This effectively flushes the ENTIRE TLB for the MM at the
 * cost of (possibly) a large number of future TLBmisses.
 *
 * The current algorithm is optimized based on the following (somewhat true)
 * assumptions:
 *         - GRU contexts are not loaded into a GRU unless a reference is made to
 *           the data segment or control block (this is true, not an assumption).
 *           If a DS/CB is referenced, the user will also issue instructions that
 *           cause TLBmisses. It is not necessary to optimize for the case where
 *           contexts are loaded but no instructions cause TLB misses. (I know
 *           this will happen but I'm not optimizing for it).
 *         - GRU instructions to invalidate TLB entries are SLOOOOWWW - normally
 *           a few usec but in unusual cases, it could be longer. Avoid if
 *           possible.
 *         - intrablade process migration between cpus is not frequent but is
 *           common.
 *         - a GRU context is not typically migrated to a different GRU on the
 *           blade because of intrablade migration
 *        - interblade migration is rare. Processes migrate their GRU context to
 *          the new blade.
 *        - if interblade migration occurs, migration back to the original blade
 *          is very very rare (ie., no optimization for this case)
 *        - most GRU instruction operate on a subset of the user REGIONS. Code
 *          & shared library regions are not likely targets of GRU instructions.
 *
 * To help improve the efficiency of TLB invalidation, the GMS data
 * structure is maintained for EACH address space (MM struct). The GMS is
 * also the structure that contains the pointer to the mmu callout
 * functions. This structure is linked to the mm_struct for the address space
 * using the mmu "register" function. The mmu interfaces are used to
 * provide the callbacks for TLB invalidation. The GMS contains:
 *
 *         - asid[maxgrus] array. ASIDs are assigned to a GRU when a context is
 *           loaded into the GRU.
 *         - asidmap[maxgrus]. bitmap to make it easier to find non-zero asids in
 *           the above array
 *        - ctxbitmap[maxgrus]. Indicates the contexts that are currently active
 *          in the GRU for the address space. This bitmap must be passed to the
 *          GRU to do an invalidate.
 *
 * The current algorithm for invalidating TLBs is:
 *         - scan the asidmap for GRUs where the context has been loaded, ie,
 *           asid is non-zero.
 *         - for each gru found:
 *                 - if the ctxtmap is non-zero, there are active contexts in the
 *                   GRU. TLB invalidate instructions must be issued to the GRU.
 *                - if the ctxtmap is zero, no context is active. Set the ASID to
 *                  zero to force a full TLB invalidation. This is fast but will
 *                  cause a lot of TLB misses if the context is reloaded onto the
 *                  GRU
 *
 */

void gru_flush_tlb_range(struct gru_mm_struct *gms, unsigned long start,
                         unsigned long len)
{
        struct gru_state *gru;
        struct gru_mm_tracker *asids;
        struct gru_tlb_global_handle *tgh;
        unsigned long num;
        int grupagesize, pagesize, pageshift, gid, asid;

        /* ZZZ TODO - handle huge pages */
        pageshift = PAGE_SHIFT;
        pagesize = (1UL << pageshift);
        grupagesize = GRU_PAGESIZE(pageshift);
        num = min(((len + pagesize - 1) >> pageshift), GRUMAXINVAL);

        STAT(flush_tlb);
        gru_dbg(grudev, "gms %p, start 0x%lx, len 0x%lx, asidmap 0x%lx\n", gms,
                start, len, gms->ms_asidmap[0]);

        spin_lock(&gms->ms_asid_lock);
        for_each_gru_in_bitmap(gid, gms->ms_asidmap) {
                STAT(flush_tlb_gru);
                gru = GID_TO_GRU(gid);
                asids = gms->ms_asids + gid;
                asid = asids->mt_asid;
                if (asids->mt_ctxbitmap && asid) {
                        STAT(flush_tlb_gru_tgh);
                        asid = GRUASID(asid, start);
                        gru_dbg(grudev,
        "  FLUSH gruid %d, asid 0x%x, num %ld, cbmap 0x%x\n",
                                gid, asid, num, asids->mt_ctxbitmap);
                        tgh = get_lock_tgh_handle(gru);
                        tgh_invalidate(tgh, start, 0, asid, grupagesize, 0,
                                       num - 1, asids->mt_ctxbitmap);
                        get_unlock_tgh_handle(tgh);
                } else {
                        STAT(flush_tlb_gru_zero_asid);
                        asids->mt_asid = 0;
                        __clear_bit(gru->gs_gid, gms->ms_asidmap);
                        gru_dbg(grudev,
        "  CLEARASID gruid %d, asid 0x%x, cbtmap 0x%x, asidmap 0x%lx\n",
                                gid, asid, asids->mt_ctxbitmap,
                                gms->ms_asidmap[0]);
                }
        }
        spin_unlock(&gms->ms_asid_lock);
}

/*
 * Flush the entire TLB on a chiplet.
 */
void gru_flush_all_tlb(struct gru_state *gru)
{
        struct gru_tlb_global_handle *tgh;

        gru_dbg(grudev, "gru %p, gid %d\n", gru, gru->gs_gid);
        tgh = get_lock_tgh_handle(gru);
        tgh_invalidate(tgh, 0, ~0, 0, 1, 1, GRUMAXINVAL - 1, 0);
        get_unlock_tgh_handle(tgh);
        preempt_enable();
}

/*
 * MMUOPS notifier callout functions
 */
static void gru_invalidate_range_start(struct mmu_notifier *mn,
                                       struct mm_struct *mm,
                                       unsigned long start, unsigned long end)
{
        struct gru_mm_struct *gms = container_of(mn, struct gru_mm_struct,
                                                 ms_notifier);

        STAT(mmu_invalidate_range);
        atomic_inc(&gms->ms_range_active);
        gru_dbg(grudev, "gms %p, start 0x%lx, end 0x%lx, act %d\n", gms,
                start, end, atomic_read(&gms->ms_range_active));
        gru_flush_tlb_range(gms, start, end - start);
}

static void gru_invalidate_range_end(struct mmu_notifier *mn,
                                     struct mm_struct *mm, unsigned long start,
                                     unsigned long end)
{
        struct gru_mm_struct *gms = container_of(mn, struct gru_mm_struct,
                                                 ms_notifier);

        /* ..._and_test() provides needed barrier */
        (void)atomic_dec_and_test(&gms->ms_range_active);

        wake_up_all(&gms->ms_wait_queue);
        gru_dbg(grudev, "gms %p, start 0x%lx, end 0x%lx\n", gms, start, end);
}

static void gru_invalidate_page(struct mmu_notifier *mn, struct mm_struct *mm,
                                unsigned long address)
{
        struct gru_mm_struct *gms = container_of(mn, struct gru_mm_struct,
                                                 ms_notifier);

        STAT(mmu_invalidate_page);
        gru_flush_tlb_range(gms, address, PAGE_SIZE);
        gru_dbg(grudev, "gms %p, address 0x%lx\n", gms, address);
}

static void gru_release(struct mmu_notifier *mn, struct mm_struct *mm)
{
        struct gru_mm_struct *gms = container_of(mn, struct gru_mm_struct,
                                                 ms_notifier);

        gms->ms_released = 1;
        gru_dbg(grudev, "gms %p\n", gms);
}


static const struct mmu_notifier_ops gru_mmuops = {
        .invalidate_page        = gru_invalidate_page,
        .invalidate_range_start        = gru_invalidate_range_start,
        .invalidate_range_end        = gru_invalidate_range_end,
        .release                = gru_release,
};

/* Move this to the basic mmu_notifier file. But for now... */
static struct mmu_notifier *mmu_find_ops(struct mm_struct *mm,
                        const struct mmu_notifier_ops *ops)
{
        struct mmu_notifier *mn, *gru_mn = NULL;
        struct hlist_node *n;

        if (mm->mmu_notifier_mm) {
                rcu_read_lock();
                hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list,
                                         hlist)
                    if (mn->ops == ops) {
                        gru_mn = mn;
                        break;
                }
                rcu_read_unlock();
        }
        return gru_mn;
}

struct gru_mm_struct *gru_register_mmu_notifier(void)
{
        struct gru_mm_struct *gms;
        struct mmu_notifier *mn;

        mn = mmu_find_ops(current->mm, &gru_mmuops);
        if (mn) {
                gms = container_of(mn, struct gru_mm_struct, ms_notifier);
                atomic_inc(&gms->ms_refcnt);
        } else {
                gms = kzalloc(sizeof(*gms), GFP_KERNEL);
                if (gms) {
                        spin_lock_init(&gms->ms_asid_lock);
                        gms->ms_notifier.ops = &gru_mmuops;
                        atomic_set(&gms->ms_refcnt, 1);
                        init_waitqueue_head(&gms->ms_wait_queue);
                        __mmu_notifier_register(&gms->ms_notifier, current->mm);
                }
        }
        gru_dbg(grudev, "gms %p, refcnt %d\n", gms,
                atomic_read(&gms->ms_refcnt));
        return gms;
}

void gru_drop_mmu_notifier(struct gru_mm_struct *gms)
{
        gru_dbg(grudev, "gms %p, refcnt %d, released %d\n", gms,
                atomic_read(&gms->ms_refcnt), gms->ms_released);
        if (atomic_dec_return(&gms->ms_refcnt) == 0) {
                if (!gms->ms_released)
                        mmu_notifier_unregister(&gms->ms_notifier, current->mm);
                kfree(gms);
        }
}

/*
 * Setup TGH parameters. There are:
 *         - 24 TGH handles per GRU chiplet
 *         - a portion (MAX_LOCAL_TGH) of the handles are reserved for
 *           use by blade-local cpus
 *         - the rest are used by off-blade cpus. This usage is
 *           less frequent than blade-local usage.
 *
 * For now, use 16 handles for local flushes, 8 for remote flushes. If the blade
 * has less tan or equal to 16 cpus, each cpu has a unique handle that it can
 * use.
 */
#define MAX_LOCAL_TGH        16

void gru_tgh_flush_init(struct gru_state *gru)
{
        int cpus, shift = 0, n;

        cpus = uv_blade_nr_possible_cpus(gru->gs_blade_id);

        /* n = cpus rounded up to next power of 2 */
        if (cpus) {
                n = 1 << fls(cpus - 1);

                /*
                 * shift count for converting local cpu# to TGH index
                 *      0 if cpus <= MAX_LOCAL_TGH,
                 *      1 if cpus <= 2*MAX_LOCAL_TGH,
                 *      etc
                 */
                shift = max(0, fls(n - 1) - fls(MAX_LOCAL_TGH - 1));
        }
        gru->gs_tgh_local_shift = shift;

        /* first starting TGH index to use for remote purges */
        gru->gs_tgh_first_remote = (cpus + (1 << shift) - 1) >> shift;

}