FreeBSD/Linux Kernel Cross Reference
sys/arm/arm/trap-v6.c

     /*-
      * Copyright 2014 Olivier Houchard <cognet@FreeBSD.org>
      * Copyright 2014 Svatopluk Kraus <onwahe@gmail.com>
      * Copyright 2014 Michal Meloun <meloun@miracle.cz>
      * Copyright 2014 Andrew Turner <andrew@FreeBSD.org>
      * All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    #include "opt_ktrace.h"
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include <sys/param.h>
    #include <sys/bus.h>
    #include <sys/systm.h>
    #include <sys/proc.h>
    #include <sys/kernel.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #include <sys/signalvar.h>
    #include <sys/ktr.h>
    #include <sys/vmmeter.h>
    #ifdef KTRACE
    #include <sys/uio.h>
    #include <sys/ktrace.h>
    #endif
    
    #include <vm/vm.h>
    #include <vm/pmap.h>
    #include <vm/vm_kern.h>
    #include <vm/vm_map.h>
    #include <vm/vm_extern.h>
    #include <vm/vm_param.h>
    
    #include <machine/cpu.h>
    #include <machine/frame.h>
    #include <machine/machdep.h>
    #include <machine/pcb.h>
    
    #ifdef KDB
    #include <sys/kdb.h>
    #include <machine/db_machdep.h>
    #endif
    
    #ifdef KDTRACE_HOOKS
    #include <sys/dtrace_bsd.h>
    #endif
    
    extern char cachebailout[];
    
    #ifdef DEBUG
    int last_fault_code;    /* For the benefit of pmap_fault_fixup() */
    #endif
    
    struct ksig {
            int sig;
            u_long code;
            vm_offset_t     addr;
    };
    
    typedef int abort_func_t(struct trapframe *, u_int, u_int, u_int, u_int,
        struct thread *, struct ksig *);
    
    static abort_func_t abort_fatal;
    static abort_func_t abort_align;
    static abort_func_t abort_icache;
    
    struct abort {
            abort_func_t    *func;
            const char      *desc;
    };
    
    /*
     * How are the aborts handled?
     *
     * Undefined Code:
     *  - Always fatal as we do not know what does it mean.
    * Imprecise External Abort:
    *  - Always fatal, but can be handled somehow in the future.
    *    Now, due to PCIe buggy hardware, ignored.
    * Precise External Abort:
    *  - Always fatal, but who knows in the future???
    * Debug Event:
    *  - Special handling.
    * External Translation Abort (L1 & L2)
    *  - Always fatal as something is screwed up in page tables or hardware.
    * Domain Fault (L1 & L2):
    *  - Always fatal as we do not play game with domains.
    * Alignment Fault:
    *  - Everything should be aligned in kernel with exception of user to kernel
    *    and vice versa data copying, so if pcb_onfault is not set, it's fatal.
    *    We generate signal in case of abort from user mode.
    * Instruction cache maintenance:
    *  - According to manual, this is translation fault during cache maintenance
    *    operation. So, it could be really complex in SMP case and fuzzy too
    *    for cache operations working on virtual addresses. For now, we will
    *    consider this abort as fatal. In fact, no cache maintenance on
    *    not mapped virtual addresses should be called. As cache maintenance
    *    operation (except DMB, DSB, and Flush Prefetch Buffer) are priviledged,
    *    the abort is fatal for user mode as well for now. (This is good place to
    *    note that cache maintenance on virtual address fill TLB.)
    * Acces Bit (L1 & L2):
    *  - Fast hardware emulation for kernel and user mode.
    * Translation Fault (L1 & L2):
    *  - Standard fault mechanism is held including vm_fault().
    * Permission Fault (L1 & L2):
    *  - Fast hardware emulation of modify bits and in other cases, standard
    *    fault mechanism is held including vm_fault().
    */
   
   static const struct abort aborts[] = {
           {abort_fatal,   "Undefined Code (0x000)"},
           {abort_align,   "Alignment Fault"},
           {abort_fatal,   "Debug Event"},
           {NULL,          "Access Bit (L1)"},
           {NULL,          "Instruction cache maintenance"},
           {NULL,          "Translation Fault (L1)"},
           {NULL,          "Access Bit (L2)"},
           {NULL,          "Translation Fault (L2)"},
   
           {abort_fatal,   "External Abort"},
           {abort_fatal,   "Domain Fault (L1)"},
           {abort_fatal,   "Undefined Code (0x00A)"},
           {abort_fatal,   "Domain Fault (L2)"},
           {abort_fatal,   "External Translation Abort (L1)"},
           {NULL,          "Permission Fault (L1)"},
           {abort_fatal,   "External Translation Abort (L2)"},
           {NULL,          "Permission Fault (L2)"},
   
           {abort_fatal,   "TLB Conflict Abort"},
           {abort_fatal,   "Undefined Code (0x401)"},
           {abort_fatal,   "Undefined Code (0x402)"},
           {abort_fatal,   "Undefined Code (0x403)"},
           {abort_fatal,   "Undefined Code (0x404)"},
           {abort_fatal,   "Undefined Code (0x405)"},
           {abort_fatal,   "Asynchronous External Abort"},
           {abort_fatal,   "Undefined Code (0x407)"},
   
           {abort_fatal,   "Asynchronous Parity Error on Memory Access"},
           {abort_fatal,   "Parity Error on Memory Access"},
           {abort_fatal,   "Undefined Code (0x40A)"},
           {abort_fatal,   "Undefined Code (0x40B)"},
           {abort_fatal,   "Parity Error on Translation (L1)"},
           {abort_fatal,   "Undefined Code (0x40D)"},
           {abort_fatal,   "Parity Error on Translation (L2)"},
           {abort_fatal,   "Undefined Code (0x40F)"}
   };
   
   static __inline void
   call_trapsignal(struct thread *td, int sig, int code, vm_offset_t addr,
       int trapno)
   {
           ksiginfo_t ksi;
   
           CTR4(KTR_TRAP, "%s: addr: %#x, sig: %d, code: %d",
              __func__, addr, sig, code);
   
           /*
            * TODO: some info would be nice to know
            * if we are serving data or prefetch abort.
            */
   
           ksiginfo_init_trap(&ksi);
           ksi.ksi_signo = sig;
           ksi.ksi_code = code;
           ksi.ksi_addr = (void *)addr;
           ksi.ksi_trapno = trapno;
           trapsignal(td, &ksi);
   }
   
   /*
    * abort_imprecise() handles the following abort:
    *
    *  FAULT_EA_IMPREC - Imprecise External Abort
    *
    * The imprecise means that we don't know where the abort happened,
    * thus FAR is undefined. The abort should not never fire, but hot
    * plugging or accidental hardware failure can be the cause of it.
    * If the abort happens, it can even be on different (thread) context.
    * Without any additional support, the abort is fatal, as we do not
    * know what really happened.
    *
    * QQQ: Some additional functionality, like pcb_onfault but global,
    *      can be implemented. Imprecise handlers could be registered
    *      which tell us if the abort is caused by something they know
    *      about. They should return one of three codes like:
    *              FAULT_IS_MINE,
    *              FAULT_CAN_BE_MINE,
    *              FAULT_IS_NOT_MINE.
    *      The handlers should be called until some of them returns
    *      FAULT_IS_MINE value or all was called. If all handlers return
    *      FAULT_IS_NOT_MINE value, then the abort is fatal.
    */
   static __inline void
   abort_imprecise(struct trapframe *tf, u_int fsr, u_int prefetch, bool usermode)
   {
   
           /*
            * XXX - We can got imprecise abort as result of access
            * to not-present PCI/PCIe configuration space.
            */
   #if 0
           goto out;
   #endif
           abort_fatal(tf, FAULT_EA_IMPREC, fsr, 0, prefetch, curthread, NULL);
   
           /*
            * Returning from this function means that we ignore
            * the abort for good reason. Note that imprecise abort
            * could fire any time even in user mode.
            */
   
   #if 0
   out:
           if (usermode)
                   userret(curthread, tf);
   #endif
   }
   
   /*
    * abort_debug() handles the following abort:
    *
    *  FAULT_DEBUG - Debug Event
    *
    */
   static __inline void
   abort_debug(struct trapframe *tf, u_int fsr, u_int prefetch, bool usermode,
       u_int far)
   {
   
           if (usermode) {
                   struct thread *td;
   
                   td = curthread;
                   call_trapsignal(td, SIGTRAP, TRAP_BRKPT, far, FAULT_DEBUG);
                   userret(td, tf);
           } else {
   #ifdef KDB
                   kdb_trap((prefetch) ? T_BREAKPOINT : T_WATCHPOINT, 0, tf);
   #else
                   printf("No debugger in kernel.\n");
   #endif
           }
   }
   
   /*
    * Abort handler.
    *
    * FAR, FSR, and everything what can be lost after enabling
    * interrupts must be grabbed before the interrupts will be
    * enabled. Note that when interrupts will be enabled, we
    * could even migrate to another CPU ...
    *
    * TODO: move quick cases to ASM
    */
   void
   abort_handler(struct trapframe *tf, int prefetch)
   {
           struct thread *td;
           vm_offset_t far, va;
           int idx, rv;
           uint32_t fsr;
           struct ksig ksig;
           struct proc *p;
           struct pcb *pcb;
           struct vm_map *map;
           struct vmspace *vm;
           vm_prot_t ftype;
           bool usermode;
           int bp_harden, ucode;
   #ifdef INVARIANTS
           void *onfault;
   #endif
   
           VM_CNT_INC(v_trap);
           td = curthread;
   
           fsr = (prefetch) ? cp15_ifsr_get(): cp15_dfsr_get();
   #if __ARM_ARCH >= 7
           far = (prefetch) ? cp15_ifar_get() : cp15_dfar_get();
   #else
           far = (prefetch) ? TRAPF_PC(tf) : cp15_dfar_get();
   #endif
   
           idx = FSR_TO_FAULT(fsr);
           usermode = TRAPF_USERMODE(tf);  /* Abort came from user mode? */
   
           /*
            * Apply BP hardening by flushing the branch prediction cache
            * for prefaults on kernel addresses.
            */
           if (__predict_false(prefetch && far > VM_MAXUSER_ADDRESS &&
               (idx == FAULT_TRAN_L2 || idx == FAULT_PERM_L2))) {
                   bp_harden = PCPU_GET(bp_harden_kind);
                   if (bp_harden == PCPU_BP_HARDEN_KIND_BPIALL)
                           _CP15_BPIALL();
                   else if (bp_harden == PCPU_BP_HARDEN_KIND_ICIALLU)
                           _CP15_ICIALLU();
           }
   
           if (usermode)
                   td->td_frame = tf;
   
           CTR6(KTR_TRAP, "%s: fsr %#x (idx %u) far %#x prefetch %u usermode %d",
               __func__, fsr, idx, far, prefetch, usermode);
   
           /*
            * Firstly, handle aborts that are not directly related to mapping.
            */
           if (__predict_false(idx == FAULT_EA_IMPREC)) {
                   abort_imprecise(tf, fsr, prefetch, usermode);
                   return;
           }
   
           if (__predict_false(idx == FAULT_DEBUG)) {
                   abort_debug(tf, fsr, prefetch, usermode, far);
                   return;
           }
   
           /*
            * ARM has a set of unprivileged load and store instructions
            * (LDRT/LDRBT/STRT/STRBT ...) which are supposed to be used in other
            * than user mode and OS should recognize their aborts and behave
            * appropriately. However, there is no way how to do that reasonably
            * in general unless we restrict the handling somehow.
            *
            * For now, these instructions are used only in copyin()/copyout()
            * like functions where usermode buffers are checked in advance that
            * they are not from KVA space. Thus, no action is needed here.
            */
   
           /*
            * (1) Handle access and R/W hardware emulation aborts.
            * (2) Check that abort is not on pmap essential address ranges.
            *     There is no way how to fix it, so we don't even try.
            */
           rv = pmap_fault(PCPU_GET(curpmap), far, fsr, idx, usermode);
           if (rv == KERN_SUCCESS)
                   return;
   #ifdef KDB
           if (kdb_active) {
                   kdb_reenter();
                   goto out;
           }
   #endif
           if (rv == KERN_INVALID_ADDRESS)
                   goto nogo;
   
           if (__predict_false((td->td_pflags & TDP_NOFAULTING) != 0)) {
                   /*
                    * Due to both processor errata and lazy TLB invalidation when
                    * access restrictions are removed from virtual pages, memory
                    * accesses that are allowed by the physical mapping layer may
                    * nonetheless cause one spurious page fault per virtual page.
                    * When the thread is executing a "no faulting" section that
                    * is bracketed by vm_fault_{disable,enable}_pagefaults(),
                    * every page fault is treated as a spurious page fault,
                    * unless it accesses the same virtual address as the most
                    * recent page fault within the same "no faulting" section.
                    */
                   if (td->td_md.md_spurflt_addr != far ||
                       (td->td_pflags & TDP_RESETSPUR) != 0) {
                           td->td_md.md_spurflt_addr = far;
                           td->td_pflags &= ~TDP_RESETSPUR;
   
                           tlb_flush_local(far & ~PAGE_MASK);
                           return;
                   }
           } else {
                   /*
                    * If we get a page fault while in a critical section, then
                    * it is most likely a fatal kernel page fault.  The kernel
                    * is already going to panic trying to get a sleep lock to
                    * do the VM lookup, so just consider it a fatal trap so the
                    * kernel can print out a useful trap message and even get
                    * to the debugger.
                    *
                    * If we get a page fault while holding a non-sleepable
                    * lock, then it is most likely a fatal kernel page fault.
                    * If WITNESS is enabled, then it's going to whine about
                    * bogus LORs with various VM locks, so just skip to the
                    * fatal trap handling directly.
                    */
                   if (td->td_critnest != 0 ||
                       WITNESS_CHECK(WARN_SLEEPOK | WARN_GIANTOK, NULL,
                       "Kernel page fault") != 0) {
                           abort_fatal(tf, idx, fsr, far, prefetch, td, &ksig);
                           return;
                   }
           }
   
           /* Re-enable interrupts if they were enabled previously. */
           if (td->td_md.md_spinlock_count == 0) {
                   if (__predict_true(tf->tf_spsr & PSR_I) == 0)
                           enable_interrupts(PSR_I);
                   if (__predict_true(tf->tf_spsr & PSR_F) == 0)
                           enable_interrupts(PSR_F);
           }
   
           p = td->td_proc;
           if (usermode) {
                   td->td_pticks = 0;
                   if (td->td_cowgen != p->p_cowgen)
                           thread_cow_update(td);
           }
   
           /* Invoke the appropriate handler, if necessary. */
           if (__predict_false(aborts[idx].func != NULL)) {
                   if ((aborts[idx].func)(tf, idx, fsr, far, prefetch, td, &ksig))
                           goto do_trapsignal;
                   goto out;
           }
   
           /*
            * At this point, we're dealing with one of the following aborts:
            *
            *  FAULT_ICACHE   - I-cache maintenance
            *  FAULT_TRAN_xx  - Translation
            *  FAULT_PERM_xx  - Permission
            */
   
           /*
            * Don't pass faulting cache operation to vm_fault(). We don't want
            * to handle all vm stuff at this moment.
            */
           pcb = td->td_pcb;
           if (__predict_false(pcb->pcb_onfault == cachebailout)) {
                   tf->tf_r0 = far;                /* return failing address */
                   tf->tf_pc = (register_t)pcb->pcb_onfault;
                   return;
           }
   
           /* Handle remaining I-cache aborts. */
           if (idx == FAULT_ICACHE) {
                   if (abort_icache(tf, idx, fsr, far, prefetch, td, &ksig))
                           goto do_trapsignal;
                   goto out;
           }
   
           va = trunc_page(far);
           if (va >= KERNBASE) {
                   /*
                    * Don't allow user-mode faults in kernel address space.
                    */
                   if (usermode) {
                           ksig.sig = SIGSEGV;
                           ksig.code = SEGV_ACCERR;
                           goto nogo;
                   }
   
                   map = kernel_map;
           } else {
                   /*
                    * This is a fault on non-kernel virtual memory. If curproc
                    * is NULL or curproc->p_vmspace is NULL the fault is fatal.
                    */
                   vm = (p != NULL) ? p->p_vmspace : NULL;
                   if (vm == NULL) {
                           ksig.sig = SIGSEGV;
                           ksig.code = 0;
                           goto nogo;
                   }
   
                   map = &vm->vm_map;
                   if (!usermode && (td->td_intr_nesting_level != 0 ||
                       pcb->pcb_onfault == NULL)) {
                           abort_fatal(tf, idx, fsr, far, prefetch, td, &ksig);
                           return;
                   }
           }
   
           ftype = (fsr & FSR_WNR) ? VM_PROT_WRITE : VM_PROT_READ;
           if (prefetch)
                   ftype |= VM_PROT_EXECUTE;
   
   #ifdef DEBUG
           last_fault_code = fsr;
   #endif
   
   #ifdef INVARIANTS
           onfault = pcb->pcb_onfault;
           pcb->pcb_onfault = NULL;
   #endif
   
           /* Fault in the page. */
           rv = vm_fault_trap(map, va, ftype, VM_FAULT_NORMAL, &ksig.sig,
               &ucode);
           ksig.code = ucode;
   
   #ifdef INVARIANTS
           pcb->pcb_onfault = onfault;
   #endif
   
           if (__predict_true(rv == KERN_SUCCESS))
                   goto out;
   nogo:
           if (!usermode) {
                   if (td->td_intr_nesting_level == 0 &&
                       pcb->pcb_onfault != NULL) {
                           tf->tf_r0 = rv;
                           tf->tf_pc = (int)pcb->pcb_onfault;
                           return;
                   }
                   CTR2(KTR_TRAP, "%s: vm_fault() failed with %d", __func__, rv);
                   abort_fatal(tf, idx, fsr, far, prefetch, td, &ksig);
                   return;
           }
   
           ksig.addr = far;
   
   do_trapsignal:
           call_trapsignal(td, ksig.sig, ksig.code, ksig.addr, idx);
   out:
           if (usermode)
                   userret(td, tf);
   }
   
   /*
    * abort_fatal() handles the following data aborts:
    *
    *  FAULT_DEBUG         - Debug Event
    *  FAULT_ACCESS_xx     - Acces Bit
    *  FAULT_EA_PREC       - Precise External Abort
    *  FAULT_DOMAIN_xx     - Domain Fault
    *  FAULT_EA_TRAN_xx    - External Translation Abort
    *  FAULT_EA_IMPREC     - Imprecise External Abort
    *  + all undefined codes for ABORT
    *
    * We should never see these on a properly functioning system.
    *
    * This function is also called by the other handlers if they
    * detect a fatal problem.
    *
    * Note: If 'l' is NULL, we assume we're dealing with a prefetch abort.
    */
   static int
   abort_fatal(struct trapframe *tf, u_int idx, u_int fsr, u_int far,
       u_int prefetch, struct thread *td, struct ksig *ksig)
   {
           bool usermode;
           const char *mode;
           const char *rw_mode;
   #ifdef KDB
           bool handled;
   #endif
   
           usermode = TRAPF_USERMODE(tf);
   #ifdef KDTRACE_HOOKS
           if (!usermode) {
                   if (dtrace_trap_func != NULL && (*dtrace_trap_func)(tf, far))
                           return (0);
           }
   #endif
   
           mode = usermode ? "user" : "kernel";
           rw_mode  = fsr & FSR_WNR ? "write" : "read";
           disable_interrupts(PSR_I|PSR_F);
   
           if (td != NULL) {
                   printf("Fatal %s mode data abort: '%s' on %s\n", mode,
                       aborts[idx].desc, rw_mode);
                   printf("trapframe: %p\nFSR=%08x, FAR=", tf, fsr);
                   if (idx != FAULT_EA_IMPREC)
                           printf("%08x, ", far);
                   else
                           printf("Invalid,  ");
                   printf("spsr=%08x\n", tf->tf_spsr);
           } else {
                   printf("Fatal %s mode prefetch abort at 0x%08x\n",
                       mode, tf->tf_pc);
                   printf("trapframe: %p, spsr=%08x\n", tf, tf->tf_spsr);
           }
   
           printf("r0 =%08x, r1 =%08x, r2 =%08x, r3 =%08x\n",
               tf->tf_r0, tf->tf_r1, tf->tf_r2, tf->tf_r3);
           printf("r4 =%08x, r5 =%08x, r6 =%08x, r7 =%08x\n",
               tf->tf_r4, tf->tf_r5, tf->tf_r6, tf->tf_r7);
           printf("r8 =%08x, r9 =%08x, r10=%08x, r11=%08x\n",
               tf->tf_r8, tf->tf_r9, tf->tf_r10, tf->tf_r11);
           printf("r12=%08x, ", tf->tf_r12);
   
           if (usermode)
                   printf("usp=%08x, ulr=%08x",
                       tf->tf_usr_sp, tf->tf_usr_lr);
           else
                   printf("ssp=%08x, slr=%08x",
                       tf->tf_svc_sp, tf->tf_svc_lr);
           printf(", pc =%08x\n\n", tf->tf_pc);
   
   #ifdef KDB
           if (debugger_on_trap) {
                   kdb_why = KDB_WHY_TRAP;
                   handled = kdb_trap(fsr, 0, tf);
                   kdb_why = KDB_WHY_UNSET;
                   if (handled)
                           return (0);
           }
   #endif
           panic("Fatal abort");
           /*NOTREACHED*/
   }
   
   /*
    * abort_align() handles the following data abort:
    *
    *  FAULT_ALIGN - Alignment fault
    *
    * Everything should be aligned in kernel with exception of user to kernel 
    * and vice versa data copying, so if pcb_onfault is not set, it's fatal.
    * We generate signal in case of abort from user mode.
    */
   static int
   abort_align(struct trapframe *tf, u_int idx, u_int fsr, u_int far,
       u_int prefetch, struct thread *td, struct ksig *ksig)
   {
           bool usermode;
   
           usermode = TRAPF_USERMODE(tf);
           if (!usermode) {
                   if (td->td_intr_nesting_level == 0 && td != NULL &&
                       td->td_pcb->pcb_onfault != NULL) {
                           tf->tf_r0 = EFAULT;
                           tf->tf_pc = (int)td->td_pcb->pcb_onfault;
                           return (0);
                   }
                   abort_fatal(tf, idx, fsr, far, prefetch, td, ksig);
           }
           /* Deliver a bus error signal to the process */
           ksig->code = BUS_ADRALN;
           ksig->sig = SIGBUS;
           ksig->addr = far;
           return (1);
   }
   
   /*
    * abort_icache() handles the following data abort:
    *
    * FAULT_ICACHE - Instruction cache maintenance
    *
    * According to manual, FAULT_ICACHE is translation fault during cache
    * maintenance operation. In fact, no cache maintenance operation on
    * not mapped virtual addresses should be called. As cache maintenance
    * operation (except DMB, DSB, and Flush Prefetch Buffer) are priviledged,
    * the abort is concider as fatal for now. However, all the matter with
    * cache maintenance operation on virtual addresses could be really complex
    * and fuzzy in SMP case, so maybe in future standard fault mechanism
    * should be held here including vm_fault() calling.
    */
   static int
   abort_icache(struct trapframe *tf, u_int idx, u_int fsr, u_int far,
       u_int prefetch, struct thread *td, struct ksig *ksig)
   {
   
           abort_fatal(tf, idx, fsr, far, prefetch, td, ksig);
           return(0);
   }

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