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SubjectRe: [PATCH] MIPS: fix pmd_mkinvalid
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On 2022/7/12 下午7:19, Thomas Bogendoerfer wrote:
> On Tue, Jul 12, 2022 at 06:01:08PM +0800, Hongchen Zhang wrote:
>> On 2022/7/7 下午7:12, Hongchen Zhang wrote:
>>> On 2022/7/7 下午5:22, Thomas Bogendoerfer wrote:
>>>> On Thu, Jul 07, 2022 at 04:11:35PM +0800, Hongchen Zhang wrote:
>>>>> When a pmd entry is invalidated by pmd_mkinvalid,pmd_present should
>>>>> return true.
>>>>> So introduce a _PMD_PRESENT_INVALID_SHIFT bit to check if a pmd is
>>>>> present but invalidated by pmd_mkinvalid.
>>>>
>>>> What problem are you trying to fix ? What are the symptoms ?
>>>>
>>>>> Reported-by: kernel test robot <lkp@intel.com>
>>>>
>>>> the test robot showed problems with your last version of the patch,
>>>> which hasn't been integrated into at least the MIPS tree, so no
>>>> need to that.
>>>>
>>>> Thomas.
>>>>
>>>
>>> Hi Thomas,
>>>   The idea come from the commit:
>>>   b65399f6111b(arm64/mm: Change THP helpers to comply with generic MM
>>>  semantics).
>>>   There is an problem now:
>>>         CPU 0        CPU 1
>>>     pmdp_invalidate        do_page_fault
>>>     ...              __handle_mm_fault
>>>                     is_swap_pmd == true
>>>                     trigger VM_BUG_ON() ?
>>>     set_pmd_at
>>>   the reason is that pmd_present return true,after this commit
>>>   pmd_present will return false,and the VM_BUG_ON will not be triggered.
>>>   Like arm64 does,we can introduce a new bit to fix this.
>>>
>>> Thanks.
>> Hi Thomas,
>> Is there problem of this patch? What's your opinion of this patch?
>
> I haven't dig deeper into it, but needing more page bits is a pain
> for 32bit kernel and would make it nearly impossible to get huge
> page support there. And the description you gave me, needs to be
> in the commit description.
>
> Thomas.
>
Hi Thomas,
Thanks for your patiently review. For your question,
1. I think there may be problem when compile 32bit kernel with huge
page support,because _PAGE_HUGE_SHIFT is only defined for R4K now.
2. I will modify the commit as you said and make a v2 patch.

Thanks.
Hongchen Zhang


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