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>

diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
new file mode 100644 (file)
index 0000000..af55aab
--- /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);
+}