nios2: MMU Fault handling

/*

 * 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;

}

/*

 * 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;

	}

}