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    Subject[PATCH 08/28] nios2: MMU Fault handling
    Date
    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>
    ---
    arch/nios2/mm/extable.c | 25 +++++
    arch/nios2/mm/fault.c | 242 ++++++++++++++++++++++++++++++++++++++++++++++++
    2 files changed, 267 insertions(+)
    create mode 100644 arch/nios2/mm/extable.c
    create mode 100644 arch/nios2/mm/fault.c

    diff --git a/arch/nios2/mm/extable.c b/arch/nios2/mm/extable.c
    new file mode 100644
    index 0000000..4d2fc5a589d09492630ddff2a52a7a6a96ab6486
    --- /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 0000000..96258b18fc32204b98a70b2dcadc3cb8661539bc
    --- /dev/null
    +++ b/arch/nios2/mm/fault.c
    @@ -0,0 +1,242 @@
    +/*
    + * 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/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;
    +
    + 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)) {
    + _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;
    + }
    +}
    --
    1.8.3.2


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