ARC: Page Fault handling

This includes recent changes to make handler "retry" and/or "killable"

The killable (early exit) logic is loosely based on how SH implements it
	return if SIGKILL + either of VM_FAULT_OOM or VM_FAULT_RETRY
which is different from Hexagon implementation which would NOT early
exit for
	SIGKILL + VM_FAULT_OOM + !VM_FAULT_RETRY

credits: Non executable stack support from Simon Spooner

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

1 files changed, 228 insertions, 0 deletions

diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
new file mode 100644
index 000000000000..af55aab803d2
--- /dev/null
+++ b/arch/arc/mm/fault.c
@@ -0,0 +1,228 @@
+/* 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);
+}