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Date: Sun, 20 Sep 2009 17:34:28 +0300
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: Russell King - ARM Linux <linux@....linux.org.uk>
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 3:24 PM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> 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?
I'll test it on Monday.
Do you want to ignore IFSR? I don't think that it's a good idea. We will
get infinite loop of faults on an unexpected for kernel type of fault, like
we have now for permission faults. Better to call do_bad() in this case.
> 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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