Re: [PATCH 1/2] arm64: mm: drop VM_FAULT_BADMAP/VM_FAULT_BADACCESS

Kefeng Wang
2024-04-11T11:12:14Z

On 2024/4/11 17:59, Catalin Marinas wrote:
> On Wed, Apr 10, 2024 at 06:58:27PM +0800, Kefeng Wang wrote:
>> On 2024/4/10 9:30, Kefeng Wang wrote:
>>> On 2024/4/9 22:28, Catalin Marinas wrote:
>>>> On Sun, Apr 07, 2024 at 04:12:10PM +0800, Kefeng Wang wrote:
>>>>> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
>>>>> index 405f9aa831bd..61a2acae0dca 100644
>>>>> --- a/arch/arm64/mm/fault.c
>>>>> +++ b/arch/arm64/mm/fault.c
>>>>> @@ -500,9 +500,6 @@ static bool is_write_abort(unsigned long esr)
>>>>>       return (esr & ESR_ELx_WNR) && !(esr & ESR_ELx_CM);
>>>>>   }
>>>>> -#define VM_FAULT_BADMAP        ((__force vm_fault_t)0x010000)
>>>>> -#define VM_FAULT_BADACCESS    ((__force vm_fault_t)0x020000)
>>>>> -
>>>>>   static int __kprobes do_page_fault(unsigned long far, unsigned
>>>>> long esr,
>>>>>                      struct pt_regs *regs)
>>>>>   {
>>>>> @@ -513,6 +510,7 @@ static int __kprobes do_page_fault(unsigned
>>>>> long far, unsigned long esr,
>>>>>       unsigned int mm_flags = FAULT_FLAG_DEFAULT;
>>>>>       unsigned long addr = untagged_addr(far);
>>>>>       struct vm_area_struct *vma;
>>>>> +    int si_code;
>>>>
>>>> I think we should initialise this to 0. Currently all paths seem to set
>>>> si_code to something meaningful but I'm not sure the last 'else' close
>>>> in this patch is guaranteed to always cover exactly those earlier code
>>>> paths updating si_code. I'm not talking about the 'goto bad_area' paths
>>>> since they set 'fault' to 0 but the fall through after the second (under
>>>> the mm lock) handle_mm_fault().
> [...]
>>>>> +    fault = handle_mm_fault(vma, addr, mm_flags, regs);
>>>>>       /* Quick path to respond to signals */
>>>>>       if (fault_signal_pending(fault, regs)) {
>>>>>           if (!user_mode(regs))
>>>>> @@ -626,13 +628,11 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
>>>>>       mmap_read_unlock(mm);
>>>>>   done:
>>>>> -    /*
>>>>> -     * Handle the "normal" (no error) case first.
>>>>> -     */
>>>>> -    if (likely(!(fault & (VM_FAULT_ERROR | VM_FAULT_BADMAP |
>>>>> -                  VM_FAULT_BADACCESS))))
>>>>> +    /* Handle the "normal" (no error) case first. */
>>>>> +    if (likely(!(fault & VM_FAULT_ERROR)))
>>>>>           return 0;
>>
>> Another choice, we set si_code = SEGV_MAPERR here, since normal
>> pagefault don't use si_code, only the error patch need to initialize.
>
> Yes, I think initialising it here would be fine. That's the fall-through
> case I was concerned about. All the other goto bad_area places already
> initialise si_code.
>
Thanks for your confirm, will send v2 soon.