On Tue, Apr 19, 2022 at 06:01:14PM -0400, Peter Xu wrote: > On Tue, Apr 19, 2022 at 05:24:28PM -0400, Johannes Weiner wrote: > > On Tue, Apr 19, 2022 at 04:28:16PM -0400, Peter Xu wrote: > > > On Tue, Apr 19, 2022 at 04:14:11PM -0400, Johannes Weiner wrote: > > > > On Tue, Apr 19, 2022 at 03:59:21PM -0400, Peter Xu wrote: > > > > > @@ -910,16 +910,16 @@ config ANON_VMA_NAME > > > > Btw, this doesn't do much without userfaultfd being enabled in > > > > general, right? > > > > > > So far yes, but I'm thinking there can be potential other users of > > > PTE_MARKERS from mm world. The most close discussion is on the swap read > > > failures and this patch proposed by Miaohe: > > > > > > https://lore.kernel.org/lkml/20220416030549.60559-1-linmiaohe@xxxxxxxxxx/ > > > > > > So I hope we can still keep them around here under mm/ if possible, and > > > from the gut feeling it really should.. > > > > Agreed, mm/ seems a good fit for PTE_MARKER. > > > > If it's invisible and gets selected as needed, it's less of a concern, > > IMO. I'm somewhat worried about when and how the user-visible options > > show up right now, though... > > > > > > Would it make sense to have it next to 'config USERFAULTFD' as a > > > > sub-option? > > > > > > Yes another good question. :) > > > > > > IIUC CONFIG_USERFAULTFD resides in init/Kconfig because it introduces a new > > > syscall. Same to the rest of the bits for uffd since then, namely: > > > > > > - USERFAULTFD_WP > > > - USERFAULTFD_MINOR > > > > > > What I am thinking now is the other way round of your suggestion: whether > > > we should move most of them out, at least the _WP and _MINOR configs into > > > mm/? Because IMHO they are really pure mm ideas and they're irrelevant to > > > syscalls and init. > > > > I'm thinking the MM submenu would probably be a better fit for all > > user-visible userfaultfd options, including the syscall. Like you say, > > it's an MM concept. > > > > But if moving the syscall knob out from init isn't popular, IMO it > > would be better to add the new WP option to init as well. This ensures > > that when somebody selects userfaultfd, they also see the relevant > > suboptions and don't have to chase them down across multiple submenus. > > > > Conversely, they should also have the necessary depend clauses so that > > suboptions aren't visible without the main feature. E.g. it asked me > > for userfaultd options even though I have CONFIG_USERFAULTFD=n. > > Hmm, this is a bit weird... since we do have that dependency chain for > PTE_MARKER_UFFD_WP -> HAVE_ARCH_USERFAULTFD_WP -> USERFAULTFD: > > in arch/x86/Kconfig: > config X86 > ... > select HAVE_ARCH_USERFAULTFD_WP if X86_64 && USERFAULTFD > > in mm/Kconfig (with/without the "mm/uffd: Hide PTE_MARKER" patch applied): > config PTE_MARKER_UFFD_WP > ... > depends on HAVE_ARCH_USERFAULTFD_WP > > So logically if !USERFAULTFD we shouldn't see PTE_MARKER_UFFD_WP at all? > > That's also what I got when I tried it out for either !USERFAULTFD on x86, > or any non-x86 platforms (because there we have !HAVE_ARCH_USERFAULTFD_WP > constantly irrelevant of USERFAULTFD). Though I could have missed > something.. Sorry, it asked me about PTE_MARKERS, and that conclusion got stuck in my head. Indeed, once that symbol is invisible we should be good. > > What do you think? > > I don't have a strong preference here, I think it's okay if it's preferred > that we only put user-visible configs into mm/Kconfig. It's just that I > see we have tons of user-invisible configs already in mm/Kconfig, to list > some: > > config ARCH_HAS_HUGEPD > config MAPPING_DIRTY_HELPERS > config KMAP_LOCAL > config KMAP_LOCAL_NON_LINEAR_PTE_ARRAY > > But I'm not sure whether it's a rule of thumb somewhere else. I wasn't objecting to invisible symbols in mm/. My point was simply that for the user it might be easiest and most intuitive if userfaultfd and its related suboptions are 1) grouped together and 2) in the MM submenu. > At the meantime, I also looked at whether syscall configs are always and > only be put under init/, and funnily I got: > > $ find . -name Kconfig | xargs grep --color -E "\".*syscall.*\"" > ./init/Kconfig: bool "Enable process_vm_readv/writev syscalls" > ./init/Kconfig: bool "uselib syscall" > ./init/Kconfig: bool "sgetmask/ssetmask syscalls support" if EXPERT > ./init/Kconfig: bool "Sysfs syscall support" if EXPERT > ./init/Kconfig: bool "open by fhandle syscalls" if EXPERT > ./init/Kconfig: bool "Enable madvise/fadvise syscalls" if EXPERT > ./arch/xtensa/Kconfig: bool "Enable fast atomic syscalls" > ./arch/xtensa/Kconfig: bool "Enable spill registers syscall" > ./arch/powerpc/Kconfig: bool "Support setting protections for 4k subpages (subpage_prot syscall)" > ./arch/powerpc/Kconfig: bool "Enable filtering of RTAS syscalls" > ./arch/Kconfig: bool "Support for randomizing kernel stack offset on syscall entry" if EXPERT > ./arch/s390/Kconfig: bool "Verify kernel signature during kexec_file_load() syscall" > ./arch/sh/mm/Kconfig: bool "Support vsyscall page" > ./arch/x86/Kconfig: bool "Enable vsyscall emulation" if EXPERT > ./arch/x86/Kconfig: bool "Verify kernel signature during kexec_file_load() syscall" > ./arch/x86/Kconfig: bool "Require a valid signature in kexec_file_load() syscall" > ./arch/x86/Kconfig: prompt "vsyscall table for legacy applications" > ./arch/arm64/Kconfig: bool "Verify kernel signature during kexec_file_load() syscall" > ./arch/arm64/Kconfig: bool "Enable the tagged user addresses syscall ABI" > ./kernel/trace/Kconfig: bool "Trace syscalls" > ./kernel/trace/Kconfig: bool "Run selftest on syscall events" > > So let's put aside arch specific lines, ftrace does have FTRACE_SYSCALLS > that lies in the kernel/trace/ dir.. not sure whether we could move > USERFAULTFD and all the rest into mm/ as well? Or perhaps that's just a > bad example? :) Yeah it looks like there is a healthy mix ;) To add to the list: - mm/Kconfig has CONFIG_SWAP for the swapon/swapoff syscalls. - fs/Kconfig has CONFIG_FILE_LOCKING, which adds the flock() syscall. - Interestingly, fs/Kconfig has CONFIG_MEMFD_CREATE for memfd_create() which is implemented in mm/memfd.c. It seems reasonable to me to move the userfaultfd stuff to mm as well, especially when it's becoming more than just a single binary question on whether you want a syscall or not, and has MM-specific suboptions.
