nios2: MMU Fault handling

This patch adds support for the handling of the MMU faults (exception
entry code introduced by a previous patch, kernel/entry.S).

Signed-off-by: Ley Foon Tan <lftan@altera.com>

2 files changed, 276 insertions, 0 deletions

diff --git a/arch/nios2/mm/extable.c b/arch/nios2/mm/extable.c
new file mode 100644
index 000000000000..4d2fc5a589d0
--- /dev/null
+++ b/arch/nios2/mm/extable.c
@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2010, Tobias Klauser <tklauser@distanz.ch>
+ * Copyright (C) 2009, Wind River Systems Inc
+ *   Implemented by fredrik.markstrom@gmail.com and ivarholmqvist@gmail.com
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ */
+
+#include <linux/module.h>
+#include <linux/uaccess.h>
+
+int fixup_exception(struct pt_regs *regs)
+{
+        const struct exception_table_entry *fixup;
+
+        fixup = search_exception_tables(regs->ea);
+        if (fixup) {
+                regs->ea = fixup->fixup;
+                return 1;
+        }
+
+        return 0;
+}
diff --git a/arch/nios2/mm/fault.c b/arch/nios2/mm/fault.c
new file mode 100644
index 000000000000..15a0bb5fc06d
--- /dev/null
+++ b/arch/nios2/mm/fault.c
@@ -0,0 +1,251 @@
+/*
+ * Copyright (C) 2009 Wind River Systems Inc
+ *   Implemented by fredrik.markstrom@gmail.com and ivarholmqvist@gmail.com
+ *
+ * based on arch/mips/mm/fault.c which is:
+ *
+ * Copyright (C) 1995-2000 Ralf Baechle
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ */
+
+#include <linux/signal.h>
+#include <linux/sched.h>
+#include <linux/interrupt.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <linux/ptrace.h>
+#include <linux/mman.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <linux/ptrace.h>
+
+#include <asm/mmu_context.h>
+#include <asm/traps.h>
+
+#define EXC_SUPERV_INSN_ACCESS  9  /* Supervisor only instruction address */
+#define EXC_SUPERV_DATA_ACCESS  11 /* Supervisor only data address */
+#define EXC_X_PROTECTION_FAULT  13 /* TLB permission violation (x) */
+#define EXC_R_PROTECTION_FAULT  14 /* TLB permission violation (r) */
+#define EXC_W_PROTECTION_FAULT  15 /* TLB permission violation (w) */
+
+/*
+ * This routine handles page faults.  It determines the address,
+ * and the problem, and then passes it off to one of the appropriate
+ * routines.
+ */
+asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long cause,
+                                unsigned long address)
+{
+        struct vm_area_struct *vma = NULL;
+        struct task_struct *tsk = current;
+        struct mm_struct *mm = tsk->mm;
+        int code = SEGV_MAPERR;
+        int fault;
+        unsigned int flags = 0;
+
+        cause >>= 2;
+
+        /* Restart the instruction */
+        regs->ea -= 4;
+
+        /*
+         * We fault-in kernel-space virtual memory on-demand. The
+         * 'reference' page table is init_mm.pgd.
+         *
+         * NOTE! We MUST NOT take any locks for this case. We may
+         * be in an interrupt or a critical region, and should
+         * only copy the information from the master page table,
+         * nothing more.
+         */
+        if (unlikely(address >= VMALLOC_START && address <= VMALLOC_END)) {
+                if (user_mode(regs))
+                        goto bad_area_nosemaphore;
+                else
+                        goto vmalloc_fault;
+        }
+
+        if (unlikely(address >= TASK_SIZE))
+                goto bad_area_nosemaphore;
+
+        /*
+         * If we're in an interrupt or have no user
+         * context, we must not take the fault..
+         */
+        if (in_atomic() || !mm)
+                goto bad_area_nosemaphore;
+
+        if (user_mode(regs))
+                flags |= FAULT_FLAG_USER;
+
+        if (!down_read_trylock(&mm->mmap_sem)) {
+                if (!user_mode(regs) && !search_exception_tables(regs->ea))
+                        goto bad_area_nosemaphore;
+                down_read(&mm->mmap_sem);
+        }
+
+        vma = find_vma(mm, address);
+        if (!vma)
+                goto bad_area;
+        if (vma->vm_start <= address)
+                goto good_area;
+        if (!(vma->vm_flags & VM_GROWSDOWN))
+                goto bad_area;
+        if (expand_stack(vma, address))
+                goto bad_area;
+/*
+ * Ok, we have a good vm_area for this memory access, so
+ * we can handle it..
+ */
+good_area:
+        code = SEGV_ACCERR;
+
+        switch (cause) {
+        case EXC_SUPERV_INSN_ACCESS:
+                goto bad_area;
+        case EXC_SUPERV_DATA_ACCESS:
+                goto bad_area;
+        case EXC_X_PROTECTION_FAULT:
+                if (!(vma->vm_flags & VM_EXEC))
+                        goto bad_area;
+                break;
+        case EXC_R_PROTECTION_FAULT:
+                if (!(vma->vm_flags & VM_READ))
+                        goto bad_area;
+                break;
+        case EXC_W_PROTECTION_FAULT:
+                if (!(vma->vm_flags & VM_WRITE))
+                        goto bad_area;
+                flags = FAULT_FLAG_WRITE;
+                break;
+        }
+
+survive:
+        /*
+         * If for any reason at all we couldn't handle the fault,
+         * make sure we exit gracefully rather than endlessly redo
+         * the fault.
+         */
+        fault = handle_mm_fault(mm, vma, address, flags);
+        if (unlikely(fault & VM_FAULT_ERROR)) {
+                if (fault & VM_FAULT_OOM)
+                        goto out_of_memory;
+                else if (fault & VM_FAULT_SIGBUS)
+                        goto do_sigbus;
+                BUG();
+        }
+        if (fault & VM_FAULT_MAJOR)
+                tsk->maj_flt++;
+        else
+                tsk->min_flt++;
+
+        up_read(&mm->mmap_sem);
+        return;
+
+/*
+ * Something tried to access memory that isn't in our memory map..
+ * Fix it, but check if it's kernel or user first..
+ */
+bad_area:
+        up_read(&mm->mmap_sem);
+
+bad_area_nosemaphore:
+        /* User mode accesses just cause a SIGSEGV */
+        if (user_mode(regs)) {
+                pr_alert("%s: unhandled page fault (%d) at 0x%08lx, "
+                        "cause %ld\n", current->comm, SIGSEGV, address, cause);
+                show_regs(regs);
+                _exception(SIGSEGV, regs, code, address);
+                return;
+        }
+
+no_context:
+        /* Are we prepared to handle this kernel fault? */
+        if (fixup_exception(regs))
+                return;
+
+        /*
+         * Oops. The kernel tried to access some bad page. We'll have to
+         * terminate things with extreme prejudice.
+         */
+        bust_spinlocks(1);
+
+        pr_alert("Unable to handle kernel %s at virtual address %08lx",
+                address < PAGE_SIZE ? "NULL pointer dereference" :
+                "paging request", address);
+        pr_alert("ea = %08lx, ra = %08lx, cause = %ld\n", regs->ea, regs->ra,
+                cause);
+        panic("Oops");
+        return;
+
+/*
+ * We ran out of memory, or some other thing happened to us that made
+ * us unable to handle the page fault gracefully.
+ */
+out_of_memory:
+        up_read(&mm->mmap_sem);
+        if (is_global_init(tsk)) {
+                yield();
+                down_read(&mm->mmap_sem);
+                goto survive;
+        }
+        if (!user_mode(regs))
+                goto no_context;
+        pagefault_out_of_memory();
+        return;
+
+do_sigbus:
+        up_read(&mm->mmap_sem);
+
+        /* Kernel mode? Handle exceptions or die */
+        if (!user_mode(regs))
+                goto no_context;
+
+        _exception(SIGBUS, regs, BUS_ADRERR, address);
+        return;
+
+vmalloc_fault:
+        {
+                /*
+                 * Synchronize this task's top level page-table
+                 * with the 'reference' page table.
+                 *
+                 * Do _not_ use "tsk" here. We might be inside
+                 * an interrupt in the middle of a task switch..
+                 */
+                int offset = pgd_index(address);
+                pgd_t *pgd, *pgd_k;
+                pud_t *pud, *pud_k;
+                pmd_t *pmd, *pmd_k;
+                pte_t *pte_k;
+
+                pgd = pgd_current + offset;
+                pgd_k = init_mm.pgd + offset;
+
+                if (!pgd_present(*pgd_k))
+                        goto no_context;
+                set_pgd(pgd, *pgd_k);
+
+                pud = pud_offset(pgd, address);
+                pud_k = pud_offset(pgd_k, address);
+                if (!pud_present(*pud_k))
+                        goto no_context;
+                pmd = pmd_offset(pud, address);
+                pmd_k = pmd_offset(pud_k, address);
+                if (!pmd_present(*pmd_k))
+                        goto no_context;
+                set_pmd(pmd, *pmd_k);
+
+                pte_k = pte_offset_kernel(pmd_k, address);
+                if (!pte_present(*pte_k))
+                        goto no_context;
+
+                flush_tlb_one(address);
+                return;
+        }
+}