arch/riscv/mm/fault.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Copyright (C) 2009 Sunplus Core Technology Co., Ltd.
   4  *  Lennox Wu <lennox.wu@sunplusct.com>
   5  *  Chen Liqin <liqin.chen@sunplusct.com>
   6  * Copyright (C) 2012 Regents of the University of California
   7  */
   8
   9
  10 #include <linux/mm.h>
  11 #include <linux/kernel.h>
  12 #include <linux/interrupt.h>
  13 #include <linux/perf_event.h>
  14 #include <linux/signal.h>
  15 #include <linux/uaccess.h>
  16
  17 #include <asm/pgalloc.h>
  18 #include <asm/ptrace.h>
  19 #include <asm/tlbflush.h>
  20
  21 /*
  22  * This routine handles page faults.  It determines the address and the
  23  * problem, and then passes it off to one of the appropriate routines.
  24  */
  25 asmlinkage void do_page_fault(struct pt_regs *regs)
  26 {
  27         struct task_struct *tsk;
  28         struct vm_area_struct *vma;
  29         struct mm_struct *mm;
  30         unsigned long addr, cause;
  31         unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
  32         int code = SEGV_MAPERR;
  33         vm_fault_t fault;
  34
  35         cause = regs->scause;
  36         addr = regs->sbadaddr;
  37
  38         tsk = current;
  39         mm = tsk->mm;
  40
  41         /*
  42          * Fault-in kernel-space virtual memory on-demand.
  43          * The 'reference' page table is init_mm.pgd.
  44          *
  45          * NOTE! We MUST NOT take any locks for this case. We may
  46          * be in an interrupt or a critical region, and should
  47          * only copy the information from the master page table,
  48          * nothing more.
  49          */
  50         if (unlikely((addr >= VMALLOC_START) && (addr <= VMALLOC_END)))
  51                 goto vmalloc_fault;
  52
  53         /* Enable interrupts if they were enabled in the parent context. */
  54         if (likely(regs->sstatus & SR_SPIE))
  55                 local_irq_enable();
  56
  57         /*
  58          * If we're in an interrupt, have no user context, or are running
  59          * in an atomic region, then we must not take the fault.
  60          */
  61         if (unlikely(faulthandler_disabled() || !mm))
  62                 goto no_context;
  63
  64         if (user_mode(regs))
  65                 flags |= FAULT_FLAG_USER;
  66
  67         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
  68
  69 retry:
  70         down_read(&mm->mmap_sem);
  71         vma = find_vma(mm, addr);
  72         if (unlikely(!vma))
  73                 goto bad_area;
  74         if (likely(vma->vm_start <= addr))
  75                 goto good_area;
  76         if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
  77                 goto bad_area;
  78         if (unlikely(expand_stack(vma, addr)))
  79                 goto bad_area;
  80
  81         /*
  82          * Ok, we have a good vm_area for this memory access, so
  83          * we can handle it.
  84          */
  85 good_area:
  86         code = SEGV_ACCERR;
  87
  88         switch (cause) {
  89         case EXC_INST_PAGE_FAULT:
  90                 if (!(vma->vm_flags & VM_EXEC))
  91                         goto bad_area;
  92                 break;
  93         case EXC_LOAD_PAGE_FAULT:
  94                 if (!(vma->vm_flags & VM_READ))
  95                         goto bad_area;
  96                 break;
  97         case EXC_STORE_PAGE_FAULT:
  98                 if (!(vma->vm_flags & VM_WRITE))
  99                         goto bad_area;
 100                 flags |= FAULT_FLAG_WRITE;
 101                 break;
 102         default:
 103                 panic("%s: unhandled cause %lu", __func__, cause);
 104         }
 105
 106         /*
 107          * If for any reason at all we could not handle the fault,
 108          * make sure we exit gracefully rather than endlessly redo
 109          * the fault.
 110          */
 111         fault = handle_mm_fault(vma, addr, flags);
 112
 113         /*
 114          * If we need to retry but a fatal signal is pending, handle the
 115          * signal first. We do not need to release the mmap_sem because it
 116          * would already be released in __lock_page_or_retry in mm/filemap.c.
 117          */
 118         if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(tsk))
 119                 return;
 120
 121         if (unlikely(fault & VM_FAULT_ERROR)) {
 122                 if (fault & VM_FAULT_OOM)
 123                         goto out_of_memory;
 124                 else if (fault & VM_FAULT_SIGBUS)
 125                         goto do_sigbus;
 126                 BUG();
 127         }
 128
 129         /*
 130          * Major/minor page fault accounting is only done on the
 131          * initial attempt. If we go through a retry, it is extremely
 132          * likely that the page will be found in page cache at that point.
 133          */
 134         if (flags & FAULT_FLAG_ALLOW_RETRY) {
 135                 if (fault & VM_FAULT_MAJOR) {
 136                         tsk->maj_flt++;
 137                         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ,
 138                                       1, regs, addr);
 139                 } else {
 140                         tsk->min_flt++;
 141                         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN,
 142                                       1, regs, addr);
 143                 }
 144                 if (fault & VM_FAULT_RETRY) {
 145                         /*
 146                          * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
 147                          * of starvation.
 148                          */
 149                         flags &= ~(FAULT_FLAG_ALLOW_RETRY);
 150                         flags |= FAULT_FLAG_TRIED;
 151
 152                         /*
 153                          * No need to up_read(&mm->mmap_sem) as we would
 154                          * have already released it in __lock_page_or_retry
 155                          * in mm/filemap.c.
 156                          */
 157                         goto retry;
 158                 }
 159         }
 160
 161         up_read(&mm->mmap_sem);
 162         return;
 163
 164         /*
 165          * Something tried to access memory that isn't in our memory map.
 166          * Fix it, but check if it's kernel or user first.
 167          */
 168 bad_area:
 169         up_read(&mm->mmap_sem);
 170         /* User mode accesses just cause a SIGSEGV */
 171         if (user_mode(regs)) {
 172                 do_trap(regs, SIGSEGV, code, addr, tsk);
 173                 return;
 174         }
 175
 176 no_context:
 177         /* Are we prepared to handle this kernel fault? */
 178         if (fixup_exception(regs))
 179                 return;
 180
 181         /*
 182          * Oops. The kernel tried to access some bad page. We'll have to
 183          * terminate things with extreme prejudice.
 184          */
 185         bust_spinlocks(1);
 186         pr_alert("Unable to handle kernel %s at virtual address " REG_FMT "\n",
 187                 (addr < PAGE_SIZE) ? "NULL pointer dereference" :
 188                 "paging request", addr);
 189         die(regs, "Oops");
 190         do_exit(SIGKILL);
 191
 192         /*
 193          * We ran out of memory, call the OOM killer, and return the userspace
 194          * (which will retry the fault, or kill us if we got oom-killed).
 195          */
 196 out_of_memory:
 197         up_read(&mm->mmap_sem);
 198         if (!user_mode(regs))
 199                 goto no_context;
 200         pagefault_out_of_memory();
 201         return;
 202
 203 do_sigbus:
 204         up_read(&mm->mmap_sem);
 205         /* Kernel mode? Handle exceptions or die */
 206         if (!user_mode(regs))
 207                 goto no_context;
 208         do_trap(regs, SIGBUS, BUS_ADRERR, addr, tsk);
 209         return;
 210
 211 vmalloc_fault:
 212         {
 213                 pgd_t *pgd, *pgd_k;
 214                 pud_t *pud, *pud_k;
 215                 p4d_t *p4d, *p4d_k;
 216                 pmd_t *pmd, *pmd_k;
 217                 pte_t *pte_k;
 218                 int index;
 219
 220                 /* User mode accesses just cause a SIGSEGV */
 221                 if (user_mode(regs))
 222                         return do_trap(regs, SIGSEGV, code, addr, tsk);
 223
 224                 /*
 225                  * Synchronize this task's top level page-table
 226                  * with the 'reference' page table.
 227                  *
 228                  * Do _not_ use "tsk->active_mm->pgd" here.
 229                  * We might be inside an interrupt in the middle
 230                  * of a task switch.
 231                  */
 232                 index = pgd_index(addr);
 233                 pgd = (pgd_t *)pfn_to_virt(csr_read(CSR_SATP)) + index;
 234                 pgd_k = init_mm.pgd + index;
 235
 236                 if (!pgd_present(*pgd_k))
 237                         goto no_context;
 238                 set_pgd(pgd, *pgd_k);
 239
 240                 p4d = p4d_offset(pgd, addr);
 241                 p4d_k = p4d_offset(pgd_k, addr);
 242                 if (!p4d_present(*p4d_k))
 243                         goto no_context;
 244
 245                 pud = pud_offset(p4d, addr);
 246                 pud_k = pud_offset(p4d_k, addr);
 247                 if (!pud_present(*pud_k))
 248                         goto no_context;
 249
 250                 /*
 251                  * Since the vmalloc area is global, it is unnecessary
 252                  * to copy individual PTEs
 253                  */
 254                 pmd = pmd_offset(pud, addr);
 255                 pmd_k = pmd_offset(pud_k, addr);
 256                 if (!pmd_present(*pmd_k))
 257                         goto no_context;
 258                 set_pmd(pmd, *pmd_k);
 259
 260                 /*
 261                  * Make sure the actual PTE exists as well to
 262                  * catch kernel vmalloc-area accesses to non-mapped
 263                  * addresses. If we don't do this, this will just
 264                  * silently loop forever.
 265                  */
 266                 pte_k = pte_offset_kernel(pmd_k, addr);
 267                 if (!pte_present(*pte_k))
 268                         goto no_context;
 269
 270                 /*
 271                  * The kernel assumes that TLBs don't cache invalid
 272                  * entries, but in RISC-V, SFENCE.VMA specifies an
 273                  * ordering constraint, not a cache flush; it is
 274                  * necessary even after writing invalid entries.
 275                  * Relying on flush_tlb_fix_spurious_fault would
 276                  * suffice, but the extra traps reduce
 277                  * performance. So, eagerly SFENCE.VMA.
 278                  */
 279                 local_flush_tlb_page(addr);
 280
 281                 return;
 282         }
 283 }