On 11/13/2023 10:02 AM, Huang, Ying wrote: >>> There are other places in the kernel where the PTE is cleared, for >>> example, move_ptes() in mremap.c. IIUC, we need to audit all them. >>> >>> Another possible solution is to check PTE again with PTL held before >>> reading in file data. This will increase the overhead of major fault >>> path. Is it acceptable? >> What if we check the PTE without page table lock acquired? > The PTE is zeroed temporarily only with PTL held. So, if we acquire the > PTL in filemap_fault() and check the PTE, the PTE which is zeroed in > do_numa_page() will be non-zero now. So we can avoid the major fault. Yes. > > But, if we don't acquire the PTL, the PTE may still be zero. For do_numa_page()/change_pte_range(), it does very limit thing during PTE is cleared. Considering the code path of do_read_fault(), it's likely the PTE is none-zero. My concern to acquiring lock is that it brings extra PTL lock acquire/release for other more common cases. Regards Yin, Fengwei > > -- > Best Regards, > Huang, Ying
