powerpc: Exception hooks for context tracking subsystem

This is the exception hooks for context tracking subsystem, including
data access, program check, single step, instruction breakpoint, machine check,
alignment, fp unavailable, altivec assist, unknown exception, whose handlers
might use RCU.

This patch corresponds to
[PATCH] x86: Exception hooks for userspace RCU extended QS
  commit 6ba3c97a38803883c2eee489505796cb0a727122

But after the exception handling moved to generic code, and some changes in
following two commits:
56dd9470d7c8734f055da2a6bac553caf4a468eb
  context_tracking: Move exception handling to generic code
6c1e0256fad84a843d915414e4b5973b7443d48d
  context_tracking: Restore correct previous context state on exception exit

it is able for exception hooks to use the generic code above instead of a
redundant arch implementation.

Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 27 insertions, 14 deletions

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 229951ffc351..8726779e1409 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -32,6 +32,7 @@
 #include <linux/perf_event.h>
 #include <linux/magic.h>
 #include <linux/ratelimit.h>
+#include <linux/context_tracking.h>
 
 #include <asm/firmware.h>
 #include <asm/page.h>
@@ -196,6 +197,7 @@ static int mm_fault_error(struct pt_regs *regs, unsigned long addr, int fault)
 int __kprobes do_page_fault(struct pt_regs *regs, unsigned long address,
                             unsigned long error_code)
 {
+        enum ctx_state prev_state = exception_enter();
         struct vm_area_struct * vma;
         struct mm_struct *mm = current->mm;
         unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
@@ -204,6 +206,7 @@ int __kprobes do_page_fault(struct pt_regs *regs, unsigned long address,
         int trap = TRAP(regs);
         int is_exec = trap == 0x400;
         int fault;
+        int rc = 0;
 
 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
         /*
@@ -230,28 +233,30 @@ int __kprobes do_page_fault(struct pt_regs *regs, unsigned long address,
          * look at it
          */
         if (error_code & ICSWX_DSI_UCT) {
-                int rc = acop_handle_fault(regs, address, error_code);
+                rc = acop_handle_fault(regs, address, error_code);
                 if (rc)
-                        return rc;
+                        goto bail;
         }
 #endif /* CONFIG_PPC_ICSWX */
 
         if (notify_page_fault(regs))
-                return 0;
+                goto bail;
 
         if (unlikely(debugger_fault_handler(regs)))
-                return 0;
+                goto bail;
 
         /* On a kernel SLB miss we can only check for a valid exception entry */
-        if (!user_mode(regs) && (address >= TASK_SIZE))
-                return SIGSEGV;
+        if (!user_mode(regs) && (address >= TASK_SIZE)) {
+                rc = SIGSEGV;
+                goto bail;
+        }
 
 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE) || \
                              defined(CONFIG_PPC_BOOK3S_64))
         if (error_code & DSISR_DABRMATCH) {
                 /* breakpoint match */
                 do_break(regs, address, error_code);
-                return 0;
+                goto bail;
         }
 #endif
 
@@ -260,8 +265,10 @@ int __kprobes do_page_fault(struct pt_regs *regs, unsigned long address,
                 local_irq_enable();
 
         if (in_atomic() || mm == NULL) {
-                if (!user_mode(regs))
-                        return SIGSEGV;
+                if (!user_mode(regs)) {
+                        rc = SIGSEGV;
+                        goto bail;
+                }
                 /* in_atomic() in user mode is really bad,
                    as is current->mm == NULL. */
                 printk(KERN_EMERG "Page fault in user mode with "
@@ -417,9 +424,11 @@ good_area:
          */
         fault = handle_mm_fault(mm, vma, address, flags);
         if (unlikely(fault & (VM_FAULT_RETRY|VM_FAULT_ERROR))) {
-                int rc = mm_fault_error(regs, address, fault);
+                rc = mm_fault_error(regs, address, fault);
                 if (rc >= MM_FAULT_RETURN)
-                        return rc;
+                        goto bail;
+                else
+                        rc = 0;
         }
 
         /*
@@ -454,7 +463,7 @@ good_area:
         }
 
         up_read(&mm->mmap_sem);
-        return 0;
+        goto bail;
 
 bad_area:
         up_read(&mm->mmap_sem);
@@ -463,7 +472,7 @@ bad_area_nosemaphore:
         /* User mode accesses cause a SIGSEGV */
         if (user_mode(regs)) {
                 _exception(SIGSEGV, regs, code, address);
-                return 0;
+                goto bail;
         }
 
         if (is_exec && (error_code & DSISR_PROTFAULT))
@@ -471,7 +480,11 @@ bad_area_nosemaphore:
                                    " page (%lx) - exploit attempt? (uid: %d)\n",
                                    address, from_kuid(&init_user_ns, current_uid()));
 
-        return SIGSEGV;
+        rc = SIGSEGV;
+
+bail:
+        exception_exit(prev_state);
+        return rc;
 
 }