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@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. > 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. -- Crap can work. Given enough thrust pigs will fly, but it's not necessarily a good idea. [ RFC1925, 2.3 ]
