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mmu-context.c

/* mmu-context.c: MMU context allocation and management
 *
 * Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * 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/sched.h>
#include <linux/mm.h>
#include <asm/tlbflush.h>

#define NR_CXN    4096

static unsigned long cxn_bitmap[NR_CXN / (sizeof(unsigned long) * 8)];
static LIST_HEAD(cxn_owners_lru);
static DEFINE_SPINLOCK(cxn_owners_lock);

int __nongpreldata cxn_pinned = -1;


/*****************************************************************************/
/*
 * initialise a new context
 */
int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
{
      memset(&mm->context, 0, sizeof(mm->context));
      INIT_LIST_HEAD(&mm->context.id_link);
      mm->context.itlb_cached_pge = 0xffffffffUL;
      mm->context.dtlb_cached_pge = 0xffffffffUL;

      return 0;
} /* end init_new_context() */

/*****************************************************************************/
/*
 * make sure a kernel MMU context has a CPU context number
 * - call with cxn_owners_lock held
 */
static unsigned get_cxn(mm_context_t *ctx)
{
      struct list_head *_p;
      mm_context_t *p;
      unsigned cxn;

      if (!list_empty(&ctx->id_link)) {
            list_move_tail(&ctx->id_link, &cxn_owners_lru);
      }
      else {
            /* find the first unallocated context number
             * - 0 is reserved for the kernel
             */
            cxn = find_next_zero_bit(cxn_bitmap, NR_CXN, 1);
            if (cxn < NR_CXN) {
                  set_bit(cxn, cxn_bitmap);
            }
            else {
                  /* none remaining - need to steal someone else's cxn */
                  p = NULL;
                  list_for_each(_p, &cxn_owners_lru) {
                        p = list_entry(_p, mm_context_t, id_link);
                        if (!p->id_busy && p->id != cxn_pinned)
                              break;
                  }

                  BUG_ON(_p == &cxn_owners_lru);

                  cxn = p->id;
                  p->id = 0;
                  list_del_init(&p->id_link);
                  __flush_tlb_mm(cxn);
            }

            ctx->id = cxn;
            list_add_tail(&ctx->id_link, &cxn_owners_lru);
      }

      return ctx->id;
} /* end get_cxn() */

/*****************************************************************************/
/*
 * restore the current TLB miss handler mapped page tables into the MMU context and set up a
 * mapping for the page directory
 */
void change_mm_context(mm_context_t *old, mm_context_t *ctx, pgd_t *pgd)
{
      unsigned long _pgd;

      _pgd = virt_to_phys(pgd);

      /* save the state of the outgoing MMU context */
      old->id_busy = 0;

      asm volatile("movsg scr0,%0"   : "=r"(old->itlb_cached_pge));
      asm volatile("movsg dampr4,%0" : "=r"(old->itlb_ptd_mapping));
      asm volatile("movsg scr1,%0"   : "=r"(old->dtlb_cached_pge));
      asm volatile("movsg dampr5,%0" : "=r"(old->dtlb_ptd_mapping));

      /* select an MMU context number */
      spin_lock(&cxn_owners_lock);
      get_cxn(ctx);
      ctx->id_busy = 1;
      spin_unlock(&cxn_owners_lock);

      asm volatile("movgs %0,cxnr"   : : "r"(ctx->id));

      /* restore the state of the incoming MMU context */
      asm volatile("movgs %0,scr0"   : : "r"(ctx->itlb_cached_pge));
      asm volatile("movgs %0,dampr4" : : "r"(ctx->itlb_ptd_mapping));
      asm volatile("movgs %0,scr1"   : : "r"(ctx->dtlb_cached_pge));
      asm volatile("movgs %0,dampr5" : : "r"(ctx->dtlb_ptd_mapping));

      /* map the PGD into uncached virtual memory */
      asm volatile("movgs %0,ttbr"   : : "r"(_pgd));
      asm volatile("movgs %0,dampr3"
                 :: "r"(_pgd | xAMPRx_L | xAMPRx_M | xAMPRx_SS_16Kb |
                      xAMPRx_S | xAMPRx_C | xAMPRx_V));

} /* end change_mm_context() */

/*****************************************************************************/
/*
 * finished with an MMU context number
 */
void destroy_context(struct mm_struct *mm)
{
      mm_context_t *ctx = &mm->context;

      spin_lock(&cxn_owners_lock);

      if (!list_empty(&ctx->id_link)) {
            if (ctx->id == cxn_pinned)
                  cxn_pinned = -1;

            list_del_init(&ctx->id_link);
            clear_bit(ctx->id, cxn_bitmap);
            __flush_tlb_mm(ctx->id);
            ctx->id = 0;
      }

      spin_unlock(&cxn_owners_lock);
} /* end destroy_context() */

/*****************************************************************************/
/*
 * display the MMU context currently a process is currently using
 */
#ifdef CONFIG_PROC_FS
char *proc_pid_status_frv_cxnr(struct mm_struct *mm, char *buffer)
{
      spin_lock(&cxn_owners_lock);
      buffer += sprintf(buffer, "CXNR: %u\n", mm->context.id);
      spin_unlock(&cxn_owners_lock);

      return buffer;
} /* end proc_pid_status_frv_cxnr() */
#endif

/*****************************************************************************/
/*
 * (un)pin a process's mm_struct's MMU context ID
 */
int cxn_pin_by_pid(pid_t pid)
{
      struct task_struct *tsk;
      struct mm_struct *mm = NULL;
      int ret;

      /* unpin if pid is zero */
      if (pid == 0) {
            cxn_pinned = -1;
            return 0;
      }

      ret = -ESRCH;

      /* get a handle on the mm_struct */
      read_lock(&tasklist_lock);
      tsk = find_task_by_vpid(pid);
      if (tsk) {
            ret = -EINVAL;

            task_lock(tsk);
            if (tsk->mm) {
                  mm = tsk->mm;
                  atomic_inc(&mm->mm_users);
                  ret = 0;
            }
            task_unlock(tsk);
      }
      read_unlock(&tasklist_lock);

      if (ret < 0)
            return ret;

      /* make sure it has a CXN and pin it */
      spin_lock(&cxn_owners_lock);
      cxn_pinned = get_cxn(&mm->context);
      spin_unlock(&cxn_owners_lock);

      mmput(mm);
      return 0;
} /* end cxn_pin_by_pid() */

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