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Message-ID: <20090920122411.GA5413@n2100.arm.linux.org.uk>
Date: Sun, 20 Sep 2009 13:24:11 +0100
From: Russell King - ARM Linux <linux@....linux.org.uk>
To: "Kirill A. Shutemov" <kirill@...temov.name>
Cc: Bityutskiy Artem <Artem.Bityutskiy@...ia.com>,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
Koskinen Aaro <aaro.koskinen@...ia.com>
Subject: Re: [PATCH 1/2] ARM: Pass IFSR register to do_PrefetchAbort()
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);
}
--
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