On Tue, Nov 24, 2020 at 10:59:48AM +0000, Catalin Marinas wrote: > Hi Mike, > > On Tue, Nov 24, 2020 at 11:25:51AM +0200, Mike Rapoport wrote: > > +static vm_fault_t secretmem_fault(struct vm_fault *vmf) > > +{ > > + struct address_space *mapping = vmf->vma->vm_file->f_mapping; ... > > + > > + err = set_direct_map_invalid_noflush(page, 1); > > + if (err) > > + goto err_del_page_cache; > > On arm64, set_direct_map_default_noflush() returns 0 if !rodata_full but > no pgtable changes happen since the linear map can be a mix of small and > huge pages. The arm64 implementation doesn't break large mappings. I > presume we don't want to tell the user that the designated memory is > "secret" but the kernel silently ignored it. > > We could change the arm64 set_direct_map* to return an error, however, I > think it would be pretty unexpected for the user to get a fault when > trying to access it. It may be better to return a -ENOSYS or something > on the actual syscall if the fault-in wouldn't be allowed later. > > Alternatively, we could make the linear map always use pages on arm64, > irrespective of other config or cmdline options (maybe not justified > unless we have clear memsecret users). Yet another idea is to get > set_direct_map* to break pmd/pud mappings into pte but that's not always > possible without a stop_machine() and potentially disabling the MMU. My preference would be to check at secretmem initialization if set_direct_map_*() actually do anything and then return an error from the syscall if they are essentially nop. I'll update the patches with something like this in v12. > -- > Catalin -- Sincerely yours, Mike.