arch/powerpc/mm/icswx.c

   1 /*
   2  *  ICSWX and ACOP Management
   3  *
   4  *  Copyright (C) 2011 Anton Blanchard, IBM Corp. <anton@samba.org>
   5  *
   6  *  This program is free software; you can redistribute it and/or
   7  *  modify it under the terms of the GNU General Public License
   8  *  as published by the Free Software Foundation; either version
   9  *  2 of the License, or (at your option) any later version.
  10  *
  11  */
  12
  13 #include <linux/sched.h>
  14 #include <linux/kernel.h>
  15 #include <linux/errno.h>
  16 #include <linux/types.h>
  17 #include <linux/mm.h>
  18 #include <linux/spinlock.h>
  19 #include <linux/module.h>
  20 #include <linux/uaccess.h>
  21
  22 #include "icswx.h"
  23
  24 /*
  25  * The processor and its L2 cache cause the icswx instruction to
  26  * generate a COP_REQ transaction on PowerBus. The transaction has no
  27  * address, and the processor does not perform an MMU access to
  28  * authenticate the transaction. The command portion of the PowerBus
  29  * COP_REQ transaction includes the LPAR_ID (LPID) and the coprocessor
  30  * Process ID (PID), which the coprocessor compares to the authorized
  31  * LPID and PID held in the coprocessor, to determine if the process
  32  * is authorized to generate the transaction.  The data of the COP_REQ
  33  * transaction is 128-byte or less in size and is placed in cacheable
  34  * memory on a 128-byte cache line boundary.
  35  *
  36  * The task to use a coprocessor should use use_cop() to mark the use
  37  * of the Coprocessor Type (CT) and context switching. On a server
  38  * class processor, the PID register is used only for coprocessor
  39  * management + * and so a coprocessor PID is allocated before
  40  * executing icswx + * instruction. Drop_cop() is used to free the
  41  * coprocessor PID.
  42  *
  43  * Example:
  44  * Host Fabric Interface (HFI) is a PowerPC network coprocessor.
  45  * Each HFI have multiple windows. Each HFI window serves as a
  46  * network device sending to and receiving from HFI network.
  47  * HFI immediate send function uses icswx instruction. The immediate
  48  * send function allows small (single cache-line) packets be sent
  49  * without using the regular HFI send FIFO and doorbell, which are
  50  * much slower than immediate send.
  51  *
  52  * For each task intending to use HFI immediate send, the HFI driver
  53  * calls use_cop() to obtain a coprocessor PID for the task.
  54  * The HFI driver then allocate a free HFI window and save the
  55  * coprocessor PID to the HFI window to allow the task to use the
  56  * HFI window.
  57  *
  58  * The HFI driver repeatedly creates immediate send packets and
  59  * issues icswx instruction to send data through the HFI window.
  60  * The HFI compares the coprocessor PID in the CPU PID register
  61  * to the PID held in the HFI window to determine if the transaction
  62  * is allowed.
  63  *
  64  * When the task to release the HFI window, the HFI driver calls
  65  * drop_cop() to release the coprocessor PID.
  66  */
  67
  68 void switch_cop(struct mm_struct *next)
  69 {
  70 #ifdef CONFIG_PPC_ICSWX_PID
  71         mtspr(SPRN_PID, next->context.cop_pid);
  72 #endif
  73         mtspr(SPRN_ACOP, next->context.acop);
  74 }
  75
  76 /**
  77  * Start using a coprocessor.
  78  * @acop: mask of coprocessor to be used.
  79  * @mm: The mm the coprocessor to associate with. Most likely current mm.
  80  *
  81  * Return a positive PID if successful. Negative errno otherwise.
  82  * The returned PID will be fed to the coprocessor to determine if an
  83  * icswx transaction is authenticated.
  84  */
  85 int use_cop(unsigned long acop, struct mm_struct *mm)
  86 {
  87         int ret;
  88
  89         if (!cpu_has_feature(CPU_FTR_ICSWX))
  90                 return -ENODEV;
  91
  92         if (!mm || !acop)
  93                 return -EINVAL;
  94
  95         /* The page_table_lock ensures mm_users won't change under us */
  96         spin_lock(&mm->page_table_lock);
  97         spin_lock(mm->context.cop_lockp);
  98
  99         ret = get_cop_pid(mm);
 100         if (ret < 0)
 101                 goto out;
 102
 103         /* update acop */
 104         mm->context.acop |= acop;
 105
 106         sync_cop(mm);
 107
 108         /*
 109          * If this is a threaded process then there might be other threads
 110          * running. We need to send an IPI to force them to pick up any
 111          * change in PID and ACOP.
 112          */
 113         if (atomic_read(&mm->mm_users) > 1)
 114                 smp_call_function(sync_cop, mm, 1);
 115
 116 out:
 117         spin_unlock(mm->context.cop_lockp);
 118         spin_unlock(&mm->page_table_lock);
 119
 120         return ret;
 121 }
 122 EXPORT_SYMBOL_GPL(use_cop);
 123
 124 /**
 125  * Stop using a coprocessor.
 126  * @acop: mask of coprocessor to be stopped.
 127  * @mm: The mm the coprocessor associated with.
 128  */
 129 void drop_cop(unsigned long acop, struct mm_struct *mm)
 130 {
 131         int free_pid;
 132
 133         if (!cpu_has_feature(CPU_FTR_ICSWX))
 134                 return;
 135
 136         if (WARN_ON_ONCE(!mm))
 137                 return;
 138
 139         /* The page_table_lock ensures mm_users won't change under us */
 140         spin_lock(&mm->page_table_lock);
 141         spin_lock(mm->context.cop_lockp);
 142
 143         mm->context.acop &= ~acop;
 144
 145         free_pid = disable_cop_pid(mm);
 146         sync_cop(mm);
 147
 148         /*
 149          * If this is a threaded process then there might be other threads
 150          * running. We need to send an IPI to force them to pick up any
 151          * change in PID and ACOP.
 152          */
 153         if (atomic_read(&mm->mm_users) > 1)
 154                 smp_call_function(sync_cop, mm, 1);
 155
 156         if (free_pid != COP_PID_NONE)
 157                 free_cop_pid(free_pid);
 158
 159         spin_unlock(mm->context.cop_lockp);
 160         spin_unlock(&mm->page_table_lock);
 161 }
 162 EXPORT_SYMBOL_GPL(drop_cop);
 163
 164 static int acop_use_cop(int ct)
 165 {
 166         /* There is no alternate policy, yet */
 167         return -1;
 168 }
 169
 170 /*
 171  * Get the instruction word at the NIP
 172  */
 173 static u32 acop_get_inst(struct pt_regs *regs)
 174 {
 175         u32 inst;
 176         u32 __user *p;
 177
 178         p = (u32 __user *)regs->nip;
 179         if (!access_ok(VERIFY_READ, p, sizeof(*p)))
 180                 return 0;
 181
 182         if (__get_user(inst, p))
 183                 return 0;
 184
 185         return inst;
 186 }
 187
 188 /**
 189  * @regs: regsiters at time of interrupt
 190  * @address: storage address
 191  * @error_code: Fault code, usually the DSISR or ESR depending on
 192  *              processor type
 193  *
 194  * Return 0 if we are able to resolve the data storage fault that
 195  * results from a CT miss in the ACOP register.
 196  */
 197 int acop_handle_fault(struct pt_regs *regs, unsigned long address,
 198                       unsigned long error_code)
 199 {
 200         int ct;
 201         u32 inst = 0;
 202
 203         if (!cpu_has_feature(CPU_FTR_ICSWX)) {
 204                 pr_info("No coprocessors available");
 205                 _exception(SIGILL, regs, ILL_ILLOPN, address);
 206         }
 207
 208         if (!user_mode(regs)) {
 209                 /* this could happen if the HV denies the
 210                  * kernel access, for now we just die */
 211                 die("ICSWX from kernel failed", regs, SIGSEGV);
 212         }
 213
 214         /* Some implementations leave us a hint for the CT */
 215         ct = ICSWX_GET_CT_HINT(error_code);
 216         if (ct < 0) {
 217                 /* we have to peek at the instruction word to figure out CT */
 218                 u32 ccw;
 219                 u32 rs;
 220
 221                 inst = acop_get_inst(regs);
 222                 if (inst == 0)
 223                         return -1;
 224
 225                 rs = (inst >> (31 - 10)) & 0x1f;
 226                 ccw = regs->gpr[rs];
 227                 ct = (ccw >> 16) & 0x3f;
 228         }
 229
 230         /*
 231          * We could be here because another thread has enabled acop
 232          * but the ACOP register has yet to be updated.
 233          *
 234          * This should have been taken care of by the IPI to sync all
 235          * the threads (see smp_call_function(sync_cop, mm, 1)), but
 236          * that could take forever if there are a significant amount
 237          * of threads.
 238          *
 239          * Given the number of threads on some of these systems,
 240          * perhaps this is the best way to sync ACOP rather than whack
 241          * every thread with an IPI.
 242          */
 243         if ((acop_copro_type_bit(ct) & current->active_mm->context.acop) != 0) {
 244                 sync_cop(current->active_mm);
 245                 return 0;
 246         }
 247
 248         /* check for alternate policy */
 249         if (!acop_use_cop(ct))
 250                 return 0;
 251
 252         /* at this point the CT is unknown to the system */
 253         pr_warn("%s[%d]: Coprocessor %d is unavailable\n",
 254                 current->comm, current->pid, ct);
 255
 256         /* get inst if we don't already have it */
 257         if (inst == 0) {
 258                 inst = acop_get_inst(regs);
 259                 if (inst == 0)
 260                         return -1;
 261         }
 262
 263         /* Check if the instruction is the "record form" */
 264         if (inst & 1) {
 265                 /*
 266                  * the instruction is "record" form so we can reject
 267                  * using CR0
 268                  */
 269                 regs->ccr &= ~(0xful << 28);
 270                 regs->ccr |= ICSWX_RC_NOT_FOUND << 28;
 271
 272                 /* Move on to the next instruction */
 273                 regs->nip += 4;
 274         } else {
 275                 /*
 276                  * There is no architected mechanism to report a bad
 277                  * CT so we could either SIGILL or report nothing.
 278                  * Since the non-record version should only bu used
 279                  * for "hints" or "don't care" we should probably do
 280                  * nothing.  However, I could see how some people
 281                  * might want an SIGILL so it here if you want it.
 282                  */
 283 #ifdef CONFIG_PPC_ICSWX_USE_SIGILL
 284                 _exception(SIGILL, regs, ILL_ILLOPN, address);
 285 #else
 286                 regs->nip += 4;
 287 #endif
 288         }
 289
 290         return 0;
 291 }
 292 EXPORT_SYMBOL_GPL(acop_handle_fault);