git.oblomov.eu Git - linux-2.6/blob - arch/um/os-Linux/skas/process.c

   1 /*
   2  * Copyright (C) 2002- 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   3  * Licensed under the GPL
   4  */
   5
   6 #include <stdlib.h>
   7 #include <unistd.h>
   8 #include <sched.h>
   9 #include <errno.h>
  10 #include <string.h>
  11 #include <sys/mman.h>
  12 #include <sys/ptrace.h>
  13 #include <sys/wait.h>
  14 #include <asm/unistd.h>
  15 #include "as-layout.h"
  16 #include "chan_user.h"
  17 #include "kern_constants.h"
  18 #include "kern_util.h"
  19 #include "mem.h"
  20 #include "os.h"
  21 #include "process.h"
  22 #include "proc_mm.h"
  23 #include "ptrace_user.h"
  24 #include "registers.h"
  25 #include "skas.h"
  26 #include "skas_ptrace.h"
  27 #include "user.h"
  28 #include "sysdep/stub.h"
  29
  30 int is_skas_winch(int pid, int fd, void *data)
  31 {
  32         if (pid != getpgrp())
  33                 return 0;
  34
  35         register_winch_irq(-1, fd, -1, data, 0);
  36         return 1;
  37 }
  38
  39 static int ptrace_dump_regs(int pid)
  40 {
  41         unsigned long regs[MAX_REG_NR];
  42         int i;
  43
  44         if (ptrace(PTRACE_GETREGS, pid, 0, regs) < 0)
  45                 return -errno;
  46
  47         printk(UM_KERN_ERR "Stub registers -\n");
  48         for (i = 0; i < ARRAY_SIZE(regs); i++)
  49                 printk(UM_KERN_ERR "\t%d - %lx\n", i, regs[i]);
  50
  51         return 0;
  52 }
  53
  54 /*
  55  * Signals that are OK to receive in the stub - we'll just continue it.
  56  * SIGWINCH will happen when UML is inside a detached screen.
  57  */
  58 #define STUB_SIG_MASK ((1 << SIGVTALRM) | (1 << SIGWINCH))
  59
  60 /* Signals that the stub will finish with - anything else is an error */
  61 #define STUB_DONE_MASK ((1 << SIGUSR1) | (1 << SIGTRAP))
  62
  63 void wait_stub_done(int pid)
  64 {
  65         int n, status, err;
  66
  67         while (1) {
  68                 CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
  69                 if ((n < 0) || !WIFSTOPPED(status))
  70                         goto bad_wait;
  71
  72                 if (((1 << WSTOPSIG(status)) & STUB_SIG_MASK) == 0)
  73                         break;
  74
  75                 err = ptrace(PTRACE_CONT, pid, 0, 0);
  76                 if (err)
  77                         panic("wait_stub_done : continue failed, errno = %d\n",
  78                               errno);
  79         }
  80
  81         if (((1 << WSTOPSIG(status)) & STUB_DONE_MASK) != 0)
  82                 return;
  83
  84 bad_wait:
  85         err = ptrace_dump_regs(pid);
  86         if (err)
  87                 printk(UM_KERN_ERR "Failed to get registers from stub, "
  88                        "errno = %d\n", -err);
  89         panic("wait_stub_done : failed to wait for SIGUSR1/SIGTRAP, pid = %d, "
  90               "n = %d, errno = %d, status = 0x%x\n", pid, n, errno, status);
  91 }
  92
  93 extern unsigned long current_stub_stack(void);
  94
  95 void get_skas_faultinfo(int pid, struct faultinfo * fi)
  96 {
  97         int err;
  98
  99         if (ptrace_faultinfo) {
 100                 err = ptrace(PTRACE_FAULTINFO, pid, 0, fi);
 101                 if (err)
 102                         panic("get_skas_faultinfo - PTRACE_FAULTINFO failed, "
 103                               "errno = %d\n", errno);
 104
 105                 /* Special handling for i386, which has different structs */
 106                 if (sizeof(struct ptrace_faultinfo) < sizeof(struct faultinfo))
 107                         memset((char *)fi + sizeof(struct ptrace_faultinfo), 0,
 108                                sizeof(struct faultinfo) -
 109                                sizeof(struct ptrace_faultinfo));
 110         }
 111         else {
 112                 err = ptrace(PTRACE_CONT, pid, 0, SIGSEGV);
 113                 if (err)
 114                         panic("Failed to continue stub, pid = %d, errno = %d\n",
 115                               pid, errno);
 116                 wait_stub_done(pid);
 117
 118                 /*
 119                  * faultinfo is prepared by the stub-segv-handler at start of
 120                  * the stub stack page. We just have to copy it.
 121                  */
 122                 memcpy(fi, (void *)current_stub_stack(), sizeof(*fi));
 123         }
 124 }
 125
 126 static void handle_segv(int pid, struct uml_pt_regs * regs)
 127 {
 128         get_skas_faultinfo(pid, &regs->faultinfo);
 129         segv(regs->faultinfo, 0, 1, NULL);
 130 }
 131
 132 /*
 133  * To use the same value of using_sysemu as the caller, ask it that value
 134  * (in local_using_sysemu
 135  */
 136 static void handle_trap(int pid, struct uml_pt_regs *regs,
 137                         int local_using_sysemu)
 138 {
 139         int err, status;
 140
 141         /* Mark this as a syscall */
 142         UPT_SYSCALL_NR(regs) = PT_SYSCALL_NR(regs->gp);
 143
 144         if (!local_using_sysemu)
 145         {
 146                 err = ptrace(PTRACE_POKEUSR, pid, PT_SYSCALL_NR_OFFSET,
 147                              __NR_getpid);
 148                 if (err < 0)
 149                         panic("handle_trap - nullifying syscall failed, "
 150                               "errno = %d\n", errno);
 151
 152                 err = ptrace(PTRACE_SYSCALL, pid, 0, 0);
 153                 if (err < 0)
 154                         panic("handle_trap - continuing to end of syscall "
 155                               "failed, errno = %d\n", errno);
 156
 157                 CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
 158                 if ((err < 0) || !WIFSTOPPED(status) ||
 159                    (WSTOPSIG(status) != SIGTRAP + 0x80)) {
 160                         err = ptrace_dump_regs(pid);
 161                         if (err)
 162                                 printk(UM_KERN_ERR "Failed to get registers "
 163                                        "from process, errno = %d\n", -err);
 164                         panic("handle_trap - failed to wait at end of syscall, "
 165                               "errno = %d, status = %d\n", errno, status);
 166                 }
 167         }
 168
 169         handle_syscall(regs);
 170 }
 171
 172 extern int __syscall_stub_start;
 173
 174 static int userspace_tramp(void *stack)
 175 {
 176         void *addr;
 177         int err;
 178
 179         ptrace(PTRACE_TRACEME, 0, 0, 0);
 180
 181         signal(SIGTERM, SIG_DFL);
 182         err = set_interval();
 183         if (err)
 184                 panic("userspace_tramp - setting timer failed, errno = %d\n",
 185                       err);
 186
 187         if (!proc_mm) {
 188                 /*
 189                  * This has a pte, but it can't be mapped in with the usual
 190                  * tlb_flush mechanism because this is part of that mechanism
 191                  */
 192                 int fd;
 193                 unsigned long long offset;
 194                 fd = phys_mapping(to_phys(&__syscall_stub_start), &offset);
 195                 addr = mmap64((void *) STUB_CODE, UM_KERN_PAGE_SIZE,
 196                               PROT_EXEC, MAP_FIXED | MAP_PRIVATE, fd, offset);
 197                 if (addr == MAP_FAILED) {
 198                         printk(UM_KERN_ERR "mapping mmap stub at 0x%lx failed, "
 199                                "errno = %d\n", STUB_CODE, errno);
 200                         exit(1);
 201                 }
 202
 203                 if (stack != NULL) {
 204                         fd = phys_mapping(to_phys(stack), &offset);
 205                         addr = mmap((void *) STUB_DATA,
 206                                     UM_KERN_PAGE_SIZE, PROT_READ | PROT_WRITE,
 207                                     MAP_FIXED | MAP_SHARED, fd, offset);
 208                         if (addr == MAP_FAILED) {
 209                                 printk(UM_KERN_ERR "mapping segfault stack "
 210                                        "at 0x%lx failed, errno = %d\n",
 211                                        STUB_DATA, errno);
 212                                 exit(1);
 213                         }
 214                 }
 215         }
 216         if (!ptrace_faultinfo && (stack != NULL)) {
 217                 struct sigaction sa;
 218
 219                 unsigned long v = STUB_CODE +
 220                                   (unsigned long) stub_segv_handler -
 221                                   (unsigned long) &__syscall_stub_start;
 222
 223                 set_sigstack((void *) STUB_DATA, UM_KERN_PAGE_SIZE);
 224                 sigemptyset(&sa.sa_mask);
 225                 sigaddset(&sa.sa_mask, SIGIO);
 226                 sigaddset(&sa.sa_mask, SIGWINCH);
 227                 sigaddset(&sa.sa_mask, SIGVTALRM);
 228                 sigaddset(&sa.sa_mask, SIGUSR1);
 229                 sa.sa_flags = SA_ONSTACK;
 230                 sa.sa_handler = (void *) v;
 231                 sa.sa_restorer = NULL;
 232                 if (sigaction(SIGSEGV, &sa, NULL) < 0)
 233                         panic("userspace_tramp - setting SIGSEGV handler "
 234                               "failed - errno = %d\n", errno);
 235         }
 236
 237         kill(os_getpid(), SIGSTOP);
 238         return 0;
 239 }
 240
 241 /* Each element set once, and only accessed by a single processor anyway */
 242 #undef NR_CPUS
 243 #define NR_CPUS 1
 244 int userspace_pid[NR_CPUS];
 245
 246 int start_userspace(unsigned long stub_stack)
 247 {
 248         void *stack;
 249         unsigned long sp;
 250         int pid, status, n, flags;
 251
 252         stack = mmap(NULL, UM_KERN_PAGE_SIZE,
 253                      PROT_READ | PROT_WRITE | PROT_EXEC,
 254                      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 255         if (stack == MAP_FAILED)
 256                 panic("start_userspace : mmap failed, errno = %d", errno);
 257         sp = (unsigned long) stack + UM_KERN_PAGE_SIZE - sizeof(void *);
 258
 259         flags = CLONE_FILES;
 260         if (proc_mm)
 261                 flags |= CLONE_VM;
 262         else
 263                 flags |= SIGCHLD;
 264
 265         pid = clone(userspace_tramp, (void *) sp, flags, (void *) stub_stack);
 266         if (pid < 0)
 267                 panic("start_userspace : clone failed, errno = %d", errno);
 268
 269         do {
 270                 CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
 271                 if (n < 0)
 272                         panic("start_userspace : wait failed, errno = %d",
 273                               errno);
 274         } while (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGVTALRM));
 275
 276         if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP))
 277                 panic("start_userspace : expected SIGSTOP, got status = %d",
 278                       status);
 279
 280         if (ptrace(PTRACE_OLDSETOPTIONS, pid, NULL,
 281                    (void *) PTRACE_O_TRACESYSGOOD) < 0)
 282                 panic("start_userspace : PTRACE_OLDSETOPTIONS failed, "
 283                       "errno = %d\n", errno);
 284
 285         if (munmap(stack, UM_KERN_PAGE_SIZE) < 0)
 286                 panic("start_userspace : munmap failed, errno = %d\n", errno);
 287
 288         return pid;
 289 }
 290
 291 void userspace(struct uml_pt_regs *regs)
 292 {
 293         struct itimerval timer;
 294         unsigned long long nsecs, now;
 295         int err, status, op, pid = userspace_pid[0];
 296         /* To prevent races if using_sysemu changes under us.*/
 297         int local_using_sysemu;
 298
 299         if (getitimer(ITIMER_VIRTUAL, &timer))
 300                 printk("Failed to get itimer, errno = %d\n", errno);
 301         nsecs = timer.it_value.tv_sec * UM_NSEC_PER_SEC +
 302                 timer.it_value.tv_usec * UM_NSEC_PER_USEC;
 303         nsecs += os_nsecs();
 304
 305         while (1) {
 306                 restore_registers(pid, regs);
 307
 308                 /* Now we set local_using_sysemu to be used for one loop */
 309                 local_using_sysemu = get_using_sysemu();
 310
 311                 op = SELECT_PTRACE_OPERATION(local_using_sysemu,
 312                                              singlestepping(NULL));
 313
 314                 err = ptrace(op, pid, 0, 0);
 315                 if (err)
 316                         panic("userspace - could not resume userspace process, "
 317                               "pid=%d, ptrace operation = %d, errno = %d\n",
 318                               pid, op, errno);
 319
 320                 CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
 321                 if (err < 0)
 322                         panic("userspace - waitpid failed, errno = %d\n",
 323                               errno);
 324
 325                 regs->is_user = 1;
 326                 save_registers(pid, regs);
 327                 UPT_SYSCALL_NR(regs) = -1; /* Assume: It's not a syscall */
 328
 329                 if (WIFSTOPPED(status)) {
 330                         int sig = WSTOPSIG(status);
 331                         switch(sig) {
 332                         case SIGSEGV:
 333                                 if (PTRACE_FULL_FAULTINFO ||
 334                                     !ptrace_faultinfo) {
 335                                         get_skas_faultinfo(pid,
 336                                                            &regs->faultinfo);
 337                                         (*sig_info[SIGSEGV])(SIGSEGV, regs);
 338                                 }
 339                                 else handle_segv(pid, regs);
 340                                 break;
 341                         case SIGTRAP + 0x80:
 342                                 handle_trap(pid, regs, local_using_sysemu);
 343                                 break;
 344                         case SIGTRAP:
 345                                 relay_signal(SIGTRAP, regs);
 346                                 break;
 347                         case SIGVTALRM:
 348                                 now = os_nsecs();
 349                                 if(now < nsecs)
 350                                         break;
 351                                 block_signals();
 352                                 (*sig_info[sig])(sig, regs);
 353                                 unblock_signals();
 354                                 nsecs = timer.it_value.tv_sec *
 355                                         UM_NSEC_PER_SEC +
 356                                         timer.it_value.tv_usec *
 357                                         UM_NSEC_PER_USEC;
 358                                 nsecs += os_nsecs();
 359                                 break;
 360                         case SIGIO:
 361                         case SIGILL:
 362                         case SIGBUS:
 363                         case SIGFPE:
 364                         case SIGWINCH:
 365                                 block_signals();
 366                                 (*sig_info[sig])(sig, regs);
 367                                 unblock_signals();
 368                                 break;
 369                         default:
 370                                 printk(UM_KERN_ERR "userspace - child stopped "
 371                                        "with signal %d\n", sig);
 372                         }
 373                         pid = userspace_pid[0];
 374                         interrupt_end();
 375
 376                         /* Avoid -ERESTARTSYS handling in host */
 377                         if (PT_SYSCALL_NR_OFFSET != PT_SYSCALL_RET_OFFSET)
 378                                 PT_SYSCALL_NR(regs->gp) = -1;
 379                 }
 380         }
 381 }
 382
 383 static unsigned long thread_regs[MAX_REG_NR];
 384
 385 static int __init init_thread_regs(void)
 386 {
 387         get_safe_registers(thread_regs);
 388         /* Set parent's instruction pointer to start of clone-stub */
 389         thread_regs[REGS_IP_INDEX] = STUB_CODE +
 390                                 (unsigned long) stub_clone_handler -
 391                                 (unsigned long) &__syscall_stub_start;
 392         thread_regs[REGS_SP_INDEX] = STUB_DATA + UM_KERN_PAGE_SIZE -
 393                 sizeof(void *);
 394 #ifdef __SIGNAL_FRAMESIZE
 395         thread_regs[REGS_SP_INDEX] -= __SIGNAL_FRAMESIZE;
 396 #endif
 397         return 0;
 398 }
 399
 400 __initcall(init_thread_regs);
 401
 402 int copy_context_skas0(unsigned long new_stack, int pid)
 403 {
 404         struct timeval tv = { .tv_sec = 0, .tv_usec = UM_USEC_PER_SEC / UM_HZ };
 405         int err;
 406         unsigned long current_stack = current_stub_stack();
 407         struct stub_data *data = (struct stub_data *) current_stack;
 408         struct stub_data *child_data = (struct stub_data *) new_stack;
 409         unsigned long long new_offset;
 410         int new_fd = phys_mapping(to_phys((void *)new_stack), &new_offset);
 411
 412         /*
 413          * prepare offset and fd of child's stack as argument for parent's
 414          * and child's mmap2 calls
 415          */
 416         *data = ((struct stub_data) { .offset   = MMAP_OFFSET(new_offset),
 417                                       .fd       = new_fd,
 418                                       .timer    = ((struct itimerval)
 419                                                    { .it_value = tv,
 420                                                      .it_interval = tv }) });
 421
 422         err = ptrace_setregs(pid, thread_regs);
 423         if (err < 0)
 424                 panic("copy_context_skas0 : PTRACE_SETREGS failed, "
 425                       "pid = %d, errno = %d\n", pid, -err);
 426
 427         /* set a well known return code for detection of child write failure */
 428         child_data->err = 12345678;
 429
 430         /*
 431          * Wait, until parent has finished its work: read child's pid from
 432          * parent's stack, and check, if bad result.
 433          */
 434         err = ptrace(PTRACE_CONT, pid, 0, 0);
 435         if (err)
 436                 panic("Failed to continue new process, pid = %d, "
 437                       "errno = %d\n", pid, errno);
 438         wait_stub_done(pid);
 439
 440         pid = data->err;
 441         if (pid < 0)
 442                 panic("copy_context_skas0 - stub-parent reports error %d\n",
 443                       -pid);
 444
 445         /*
 446          * Wait, until child has finished too: read child's result from
 447          * child's stack and check it.
 448          */
 449         wait_stub_done(pid);
 450         if (child_data->err != STUB_DATA)
 451                 panic("copy_context_skas0 - stub-child reports error %ld\n",
 452                       child_data->err);
 453
 454         if (ptrace(PTRACE_OLDSETOPTIONS, pid, NULL,
 455                    (void *)PTRACE_O_TRACESYSGOOD) < 0)
 456                 panic("copy_context_skas0 : PTRACE_OLDSETOPTIONS failed, "
 457                       "errno = %d\n", errno);
 458
 459         return pid;
 460 }
 461
 462 /*
 463  * This is used only, if stub pages are needed, while proc_mm is
 464  * available. Opening /proc/mm creates a new mm_context, which lacks
 465  * the stub-pages. Thus, we map them using /proc/mm-fd
 466  */
 467 void map_stub_pages(int fd, unsigned long code,
 468                     unsigned long data, unsigned long stack)
 469 {
 470         struct proc_mm_op mmop;
 471         int n;
 472         unsigned long long code_offset;
 473         int code_fd = phys_mapping(to_phys((void *) &__syscall_stub_start),
 474                                    &code_offset);
 475
 476         mmop = ((struct proc_mm_op) { .op        = MM_MMAP,
 477                                       .u         =
 478                                       { .mmap    =
 479                                         { .addr    = code,
 480                                           .len     = UM_KERN_PAGE_SIZE,
 481                                           .prot    = PROT_EXEC,
 482                                           .flags   = MAP_FIXED | MAP_PRIVATE,
 483                                           .fd      = code_fd,
 484                                           .offset  = code_offset
 485         } } });
 486         CATCH_EINTR(n = write(fd, &mmop, sizeof(mmop)));
 487         if (n != sizeof(mmop)) {
 488                 n = errno;
 489                 printk(UM_KERN_ERR "mmap args - addr = 0x%lx, fd = %d, "
 490                        "offset = %llx\n", code, code_fd,
 491                        (unsigned long long) code_offset);
 492                 panic("map_stub_pages : /proc/mm map for code failed, "
 493                       "err = %d\n", n);
 494         }
 495
 496         if (stack) {
 497                 unsigned long long map_offset;
 498                 int map_fd = phys_mapping(to_phys((void *)stack), &map_offset);
 499                 mmop = ((struct proc_mm_op)
 500                                 { .op        = MM_MMAP,
 501                                   .u         =
 502                                   { .mmap    =
 503                                     { .addr    = data,
 504                                       .len     = UM_KERN_PAGE_SIZE,
 505                                       .prot    = PROT_READ | PROT_WRITE,
 506                                       .flags   = MAP_FIXED | MAP_SHARED,
 507                                       .fd      = map_fd,
 508                                       .offset  = map_offset
 509                 } } });
 510                 CATCH_EINTR(n = write(fd, &mmop, sizeof(mmop)));
 511                 if (n != sizeof(mmop))
 512                         panic("map_stub_pages : /proc/mm map for data failed, "
 513                               "err = %d\n", errno);
 514         }
 515 }
 516
 517 void new_thread(void *stack, jmp_buf *buf, void (*handler)(void))
 518 {
 519         (*buf)[0].JB_IP = (unsigned long) handler;
 520         (*buf)[0].JB_SP = (unsigned long) stack + UM_THREAD_SIZE -
 521                 sizeof(void *);
 522 }
 523
 524 #define INIT_JMP_NEW_THREAD 0
 525 #define INIT_JMP_CALLBACK 1
 526 #define INIT_JMP_HALT 2
 527 #define INIT_JMP_REBOOT 3
 528
 529 void switch_threads(jmp_buf *me, jmp_buf *you)
 530 {
 531         if (UML_SETJMP(me) == 0)
 532                 UML_LONGJMP(you, 1);
 533 }
 534
 535 static jmp_buf initial_jmpbuf;
 536
 537 /* XXX Make these percpu */
 538 static void (*cb_proc)(void *arg);
 539 static void *cb_arg;
 540 static jmp_buf *cb_back;
 541
 542 int start_idle_thread(void *stack, jmp_buf *switch_buf)
 543 {
 544         int n;
 545
 546         set_handler(SIGWINCH, (__sighandler_t) sig_handler,
 547                     SA_ONSTACK | SA_RESTART, SIGUSR1, SIGIO, SIGVTALRM, -1);
 548
 549         /*
 550          * Can't use UML_SETJMP or UML_LONGJMP here because they save
 551          * and restore signals, with the possible side-effect of
 552          * trying to handle any signals which came when they were
 553          * blocked, which can't be done on this stack.
 554          * Signals must be blocked when jumping back here and restored
 555          * after returning to the jumper.
 556          */
 557         n = setjmp(initial_jmpbuf);
 558         switch(n) {
 559         case INIT_JMP_NEW_THREAD:
 560                 (*switch_buf)[0].JB_IP = (unsigned long) new_thread_handler;
 561                 (*switch_buf)[0].JB_SP = (unsigned long) stack +
 562                         UM_THREAD_SIZE - sizeof(void *);
 563                 break;
 564         case INIT_JMP_CALLBACK:
 565                 (*cb_proc)(cb_arg);
 566                 longjmp(*cb_back, 1);
 567                 break;
 568         case INIT_JMP_HALT:
 569                 kmalloc_ok = 0;
 570                 return 0;
 571         case INIT_JMP_REBOOT:
 572                 kmalloc_ok = 0;
 573                 return 1;
 574         default:
 575                 panic("Bad sigsetjmp return in start_idle_thread - %d\n", n);
 576         }
 577         longjmp(*switch_buf, 1);
 578 }
 579
 580 void initial_thread_cb_skas(void (*proc)(void *), void *arg)
 581 {
 582         jmp_buf here;
 583
 584         cb_proc = proc;
 585         cb_arg = arg;
 586         cb_back = &here;
 587
 588         block_signals();
 589         if (UML_SETJMP(&here) == 0)
 590                 UML_LONGJMP(&initial_jmpbuf, INIT_JMP_CALLBACK);
 591         unblock_signals();
 592
 593         cb_proc = NULL;
 594         cb_arg = NULL;
 595         cb_back = NULL;
 596 }
 597
 598 void halt_skas(void)
 599 {
 600         block_signals();
 601         UML_LONGJMP(&initial_jmpbuf, INIT_JMP_HALT);
 602 }
 603
 604 void reboot_skas(void)
 605 {
 606         block_signals();
 607         UML_LONGJMP(&initial_jmpbuf, INIT_JMP_REBOOT);
 608 }
 609
 610 void __switch_mm(struct mm_id *mm_idp)
 611 {
 612         int err;
 613
 614         /* FIXME: need cpu pid in __switch_mm */
 615         if (proc_mm) {
 616                 err = ptrace(PTRACE_SWITCH_MM, userspace_pid[0], 0,
 617                              mm_idp->u.mm_fd);
 618                 if (err)
 619                         panic("__switch_mm - PTRACE_SWITCH_MM failed, "
 620                               "errno = %d\n", errno);
 621         }
 622         else userspace_pid[0] = mm_idp->u.pid;
 623 }