[PATCH v2 5/7] riscv: mm: accelerate pagefault when badaccess
Kefeng Wang
wangkefeng.wang at huawei.com
Wed Apr 10 18:17:56 PDT 2024
On 2024/4/11 1:28, Alexandre Ghiti wrote:
> On 10/04/2024 10:07, Kefeng Wang wrote:
>>
>>
>> On 2024/4/10 15:32, Alexandre Ghiti wrote:
>>> Hi Kefeng,
>>>
>>> On 03/04/2024 10:38, Kefeng Wang wrote:
>>>> The access_error() of vma already checked under per-VMA lock, if it
>>>> is a bad access, directly handle error, no need to retry with mmap_lock
>>>> again. Since the page faut is handled under per-VMA lock, count it as
>>>> a vma lock event with VMA_LOCK_SUCCESS.
>>>>
>>>> Reviewed-by: Suren Baghdasaryan <surenb at google.com>
>>>> Signed-off-by: Kefeng Wang <wangkefeng.wang at huawei.com>
>>>> ---
>>>> arch/riscv/mm/fault.c | 5 ++++-
>>>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
>>>> index 3ba1d4dde5dd..b3fcf7d67efb 100644
>>>> --- a/arch/riscv/mm/fault.c
>>>> +++ b/arch/riscv/mm/fault.c
>>>> @@ -292,7 +292,10 @@ void handle_page_fault(struct pt_regs *regs)
>>>> if (unlikely(access_error(cause, vma))) {
>>>> vma_end_read(vma);
>>>> - goto lock_mmap;
>>>> + count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
>>>> + tsk->thread.bad_cause = SEGV_ACCERR;
>>>
>>>
>>> I think we should use the cause variable here instead of SEGV_ACCERR,
>>> as bad_cause is a riscv internal status which describes the real
>>> fault that happened.
>>
>> Oh, I see, it is exception causes on riscv, so it should be
>>
>> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
>> index b3fcf7d67efb..5224f3733802 100644
>> --- a/arch/riscv/mm/fault.c
>> +++ b/arch/riscv/mm/fault.c
>> @@ -293,8 +293,8 @@ void handle_page_fault(struct pt_regs *regs)
>> if (unlikely(access_error(cause, vma))) {
>> vma_end_read(vma);
>> count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
>> - tsk->thread.bad_cause = SEGV_ACCERR;
>> - bad_area_nosemaphore(regs, code, addr);
>> + tsk->thread.bad_cause = cause;
>> + bad_area_nosemaphore(regs, SEGV_ACCERR, addr);
>> return;
>> }
>>
>> Hi Alex, could you help to check it?
>>
>> Hi Andrew, please help to squash it after Alex ack it.
>>
>> Thanks both.
>
>
> So I have just tested Kefeng's fixup on my usual CI and with a simple
> program that triggers such bad access, everything went fine so with the
> fixup applied:
>
> Reviewed-by: Alexandre Ghiti <alexghiti at rivosinc.com>
> Tested-by: Alexandre Ghiti <alexghiti at rivosinc.com>
Great, thanks.
>
> Thanks,
>
> Alex
>
>
>
>>
>>
>>>
>>> Thanks,
>>>
>>> Alex
>>>
>>>
>>>> + bad_area_nosemaphore(regs, code, addr);
>>>> + return;
>>>> }
>>>> fault = handle_mm_fault(vma, addr, flags |
>>>> FAULT_FLAG_VMA_LOCK, regs);
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