ARC: Page Fault handling

/* Page Fault Handling for ARC (TLB Miss / ProtV)

 *

 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation.

 */

#include <linux/signal.h>

#include <linux/interrupt.h>

#include <linux/sched.h>

#include <linux/errno.h>

#include <linux/ptrace.h>

#include <linux/version.h>

#include <linux/uaccess.h>

#include <linux/kdebug.h>

#include <asm/pgalloc.h>

static int handle_vmalloc_fault(struct mm_struct *mm, unsigned long address)

{

	/*

	 * Synchronize this task's top level page-table

	 * with the 'reference' page table.

	 */

	pgd_t *pgd, *pgd_k;

	pud_t *pud, *pud_k;

	pmd_t *pmd, *pmd_k;

	pgd = pgd_offset_fast(mm, address);

	pgd_k = pgd_offset_k(address);

	if (!pgd_present(*pgd_k))

		goto bad_area;

	pud = pud_offset(pgd, address);

	pud_k = pud_offset(pgd_k, address);

	if (!pud_present(*pud_k))

		goto bad_area;

	pmd = pmd_offset(pud, address);

	pmd_k = pmd_offset(pud_k, address);

	if (!pmd_present(*pmd_k))

		goto bad_area;

	set_pmd(pmd, *pmd_k);

	/* XXX: create the TLB entry here */

	return 0;

bad_area:

	return 1;

}

void do_page_fault(struct pt_regs *regs, int write, unsigned long address,

		   unsigned long cause_code)

{

	struct vm_area_struct *vma = NULL;

	struct task_struct *tsk = current;

	struct mm_struct *mm = tsk->mm;

	siginfo_t info;

	int fault, ret;

	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE |

				(write ? FAULT_FLAG_WRITE : 0);

	/*

	 * 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 (address >= VMALLOC_START && address <= VMALLOC_END) {

		ret = handle_vmalloc_fault(mm, address);

		if (unlikely(ret))

			goto bad_area_nosemaphore;

		else

			return;

	}

	info.si_code = SEGV_MAPERR;

	/*

	 * If we're in an interrupt or have no user

	 * context, we must not take the fault..

	 */

	if (in_atomic() || !mm)

		goto no_context;

retry:

	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:

	info.si_code = SEGV_ACCERR;

	/* Handle protection violation, execute on heap or stack */

	if (cause_code == ((ECR_V_PROTV << 16) | ECR_C_PROTV_INST_FETCH))

		goto bad_area;

	if (write) {

		if (!(vma->vm_flags & VM_WRITE))

			goto bad_area;

	} else {

		if (!(vma->vm_flags & (VM_READ | VM_EXEC)))

			goto bad_area;

	}

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 Pagefault was interrupted by SIGKILL, exit page fault "early" */

	if (unlikely(fatal_signal_pending(current))) {

		if ((fault & VM_FAULT_ERROR) && !(fault & VM_FAULT_RETRY))

			up_read(&mm->mmap_sem);

		if (user_mode(regs))

			return;

	}

	if (likely(!(fault & VM_FAULT_ERROR))) {

		if (flags & FAULT_FLAG_ALLOW_RETRY) {

			/* To avoid updating stats twice for retry case */

			if (fault & VM_FAULT_MAJOR)

				tsk->maj_flt++;

			else

				tsk->min_flt++;

			if (fault & VM_FAULT_RETRY) {

				flags &= ~FAULT_FLAG_ALLOW_RETRY;

				flags |= FAULT_FLAG_TRIED;

				goto retry;

			}

		}

		/* Fault Handled Gracefully */

		up_read(&mm->mmap_sem);

		return;

	}

	/* TBD: switch to pagefault_out_of_memory() */

	if (fault & VM_FAULT_OOM)

		goto out_of_memory;

	else if (fault & VM_FAULT_SIGBUS)

		goto do_sigbus;

	/* no man's land */

	BUG();

	/*

	 * 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)) {

		tsk->thread.fault_address = address;

		tsk->thread.cause_code = cause_code;

		info.si_signo = SIGSEGV;

		info.si_errno = 0;

		/* info.si_code has been set above */

		info.si_addr = (void __user *)address;

		force_sig_info(SIGSEGV, &info, tsk);

		return;

	}

no_context:

	/* Are we prepared to handle this kernel fault?

	 *

	 * (The kernel has valid exception-points in the source

	 *  when it acesses user-memory. When it fails in one

	 *  of those points, we find it in a table and do a jump

	 *  to some fixup code that loads an appropriate error

	 *  code)

	 */

	if (fixup_exception(regs))

		return;

	die("Oops", regs, address, cause_code);

out_of_memory:

	if (is_global_init(tsk)) {

		yield();

		goto survive;

	}

	up_read(&mm->mmap_sem);

	if (user_mode(regs))

		do_group_exit(SIGKILL);	/* This will never return */

	goto no_context;

do_sigbus:

	up_read(&mm->mmap_sem);

	if (!user_mode(regs))

		goto no_context;

	tsk->thread.fault_address = address;

	tsk->thread.cause_code = cause_code;

	info.si_signo = SIGBUS;

	info.si_errno = 0;

	info.si_code = BUS_ADRERR;

	info.si_addr = (void __user *)address;

	force_sig_info(SIGBUS, &info, tsk);

}