Re: [PATCH] MIPS: fix pmd_mkinvalid

[Hongchen Zhang]

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@xxxxxxxxx>
>
> 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.