[PATCH 1/2] ARM: Pass IFSR register to do_PrefetchAbort()

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Sun, Sep 20, 2009 at 12:35:19PM +0300, Kirill A. Shutemov wrote:
> Ok, so __do_page_fault() should know where we are: in data abort or in
> prefetch abort. What is right way to do it? Should we create one more
> argument or use one of reserved bits IFSR?

Well, this is my solution to the problem - could you test it please?
This patch is actually the result of several patches merged together,
so I won't supply a proper description etc.

diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index cc8829d..8fbb22d 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -25,6 +25,19 @@
 
 #include "fault.h"
 
+/*
+ * Fault status register encodings.  We steal bit 31 for our own purposes.
+ */
+#define FSR_LNX_PF		(1 << 31)
+#define FSR_WRITE		(1 << 11)
+#define FSR_FS4			(1 << 10)
+#define FSR_FS3_0		(15)
+
+static inline int fsr_fs(unsigned int fsr)
+{
+	return (fsr & FSR_FS3_0) | (fsr & FSR_FS4) >> 6;
+}
+
 #ifdef CONFIG_MMU
 
 #ifdef CONFIG_KPROBES
@@ -182,18 +195,35 @@ void do_bad_area(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 #define VM_FAULT_BADMAP		0x010000
 #define VM_FAULT_BADACCESS	0x020000
 
-static int
+/*
+ * Check that the permissions on the VMA allow for the fault which occurred.
+ * If we encountered a write fault, we must have write permission, otherwise
+ * we allow any permission.
+ */
+static inline bool access_error(unsigned int fsr, struct vm_area_struct *vma)
+{
+	unsigned int mask = VM_READ | VM_WRITE | VM_EXEC;
+
+	if (fsr & FSR_WRITE)
+		mask = VM_WRITE;
+	if (fsr & FSR_LNX_PF)
+		mask = VM_EXEC;
+
+	return vma->vm_flags & mask ? false : true;
+}
+
+static noinline int __kprobes
 __do_page_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
 		struct task_struct *tsk)
 {
 	struct vm_area_struct *vma;
-	int fault, mask;
+	int fault;
 
 	vma = find_vma(mm, addr);
 	fault = VM_FAULT_BADMAP;
-	if (!vma)
+	if (unlikely(!vma))
 		goto out;
-	if (vma->vm_start > addr)
+	if (unlikely(vma->vm_start > addr))
 		goto check_stack;
 
 	/*
@@ -201,47 +231,24 @@ __do_page_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
 	 * memory access, so we can handle it.
 	 */
 good_area:
-	if (fsr & (1 << 11)) /* write? */
-		mask = VM_WRITE;
-	else
-		mask = VM_READ|VM_EXEC|VM_WRITE;
-
-	fault = VM_FAULT_BADACCESS;
-	if (!(vma->vm_flags & mask))
+	if (access_error(fsr, vma)) {
+		fault = VM_FAULT_BADACCESS;
 		goto out;
+	}
 
 	/*
-	 * If for any reason at all we couldn't handle
-	 * the fault, make sure we exit gracefully rather
-	 * than endlessly redo the fault.
+	 * If for any reason at all we couldn't handle the fault, make
+	 * sure we exit gracefully rather than endlessly redo the fault.
 	 */
-survive:
-	fault = handle_mm_fault(mm, vma, addr & PAGE_MASK, (fsr & (1 << 11)) ? FAULT_FLAG_WRITE : 0);
-	if (unlikely(fault & VM_FAULT_ERROR)) {
-		if (fault & VM_FAULT_OOM)
-			goto out_of_memory;
-		else if (fault & VM_FAULT_SIGBUS)
-			return fault;
-		BUG();
-	}
+	fault = handle_mm_fault(mm, vma, addr & PAGE_MASK, (fsr & FSR_WRITE) ? FAULT_FLAG_WRITE : 0);
+	if (unlikely(fault & VM_FAULT_ERROR))
+		return fault;
 	if (fault & VM_FAULT_MAJOR)
 		tsk->maj_flt++;
 	else
 		tsk->min_flt++;
 	return fault;
 
-out_of_memory:
-	if (!is_global_init(tsk))
-		goto out;
-
-	/*
-	 * If we are out of memory for pid1, sleep for a while and retry
-	 */
-	up_read(&mm->mmap_sem);
-	yield();
-	down_read(&mm->mmap_sem);
-	goto survive;
-
 check_stack:
 	if (vma->vm_flags & VM_GROWSDOWN && !expand_stack(vma, addr))
 		goto good_area;
@@ -278,6 +285,13 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 		if (!user_mode(regs) && !search_exception_tables(regs->ARM_pc))
 			goto no_context;
 		down_read(&mm->mmap_sem);
+	} else {
+		/*
+		 * The above down_read_trylock() might have succeeded in
+		 * which case, we'll have missed the might_sleep() from
+		 * down_read()
+		 */
+		might_sleep();
 	}
 
 	fault = __do_page_fault(mm, addr, fsr, tsk);
@@ -289,6 +303,16 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 	if (likely(!(fault & (VM_FAULT_ERROR | VM_FAULT_BADMAP | VM_FAULT_BADACCESS))))
 		return 0;
 
+	if (fault & VM_FAULT_OOM) {
+		/*
+		 * We ran out of memory, call the OOM killer, and return to
+		 * userspace (which will retry the fault, or kill us if we
+		 * got oom-killed)
+		 */
+		pagefault_out_of_memory();
+		return 0;
+	}
+
 	/*
 	 * If we are in kernel mode at this point, we
 	 * have no context to handle this fault with.
@@ -296,16 +320,6 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 	if (!user_mode(regs))
 		goto no_context;
 
-	if (fault & VM_FAULT_OOM) {
-		/*
-		 * We ran out of memory, or some other thing
-		 * happened to us that made us unable to handle
-		 * the page fault gracefully.
-		 */
-		printk("VM: killing process %s\n", tsk->comm);
-		do_group_exit(SIGKILL);
-		return 0;
-	}
 	if (fault & VM_FAULT_SIGBUS) {
 		/*
 		 * We had some memory, but were unable to
@@ -489,10 +503,10 @@ hook_fault_code(int nr, int (*fn)(unsigned long, unsigned int, struct pt_regs *)
 asmlinkage void __exception
 do_DataAbort(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 {
-	const struct fsr_info *inf = fsr_info + (fsr & 15) + ((fsr & (1 << 10)) >> 6);
+	const struct fsr_info *inf = fsr_info + fsr_fs(fsr);
 	struct siginfo info;
 
-	if (!inf->fn(addr, fsr, regs))
+	if (!inf->fn(addr, fsr & ~FSR_LNX_PF, regs))
 		return;
 
 	printk(KERN_ALERT "Unhandled fault: %s (0x%03x) at 0x%08lx\n",
@@ -508,6 +522,6 @@ do_DataAbort(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 asmlinkage void __exception
 do_PrefetchAbort(unsigned long addr, struct pt_regs *regs)
 {
-	do_translation_fault(addr, 0, regs);
+	do_translation_fault(addr, FSR_LNX_PF, regs);
 }