| Message ID | 20220405014646.13522-1-peterx@redhat.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | userfaultfd-wp: Support shmem and hugetlbfs | expand |
On Mon, 4 Apr 2022 21:46:23 -0400 Peter Xu <peterx@redhat.com> wrote: > This is v8 of the series to add shmem+hugetlbfs support for userfaultfd > write protection. Various compilation catastrophes with x86_64 allnoconfig. I poked at the include ordering for a while but other things quickly became more attractive ;)
On Tue, Apr 05, 2022 at 03:16:16PM -0700, Andrew Morton wrote: > On Mon, 4 Apr 2022 21:46:23 -0400 Peter Xu <peterx@redhat.com> wrote: > > > This is v8 of the series to add shmem+hugetlbfs support for userfaultfd > > write protection. > > Various compilation catastrophes with x86_64 allnoconfig. I poked at > the include ordering for a while but other things quickly became more > attractive ;) Sorry about that. I still don't know what's the problem, but I'll give it a shot soon. I think I only tried out with the new configs but not all the rest configs. I thought there're some bot looking after that one, from which I used to receive build reports. And IIRC I fixed some build issues in early versions from those reports. Maybe I was wrong.. Any more hints on the latter? Thanks,
On Tue, 5 Apr 2022 18:42:43 -0400 Peter Xu <peterx@redhat.com> wrote: > On Tue, Apr 05, 2022 at 03:16:16PM -0700, Andrew Morton wrote: > > On Mon, 4 Apr 2022 21:46:23 -0400 Peter Xu <peterx@redhat.com> wrote: > > > > > This is v8 of the series to add shmem+hugetlbfs support for userfaultfd > > > write protection. > > > > Various compilation catastrophes with x86_64 allnoconfig. I poked at > > the include ordering for a while but other things quickly became more > > attractive ;) > > Sorry about that. I still don't know what's the problem, but I'll give it > a shot soon. > > I think I only tried out with the new configs but not all the rest configs. > I thought there're some bot looking after that one, from which I used to > receive build reports. And IIRC I fixed some build issues in early versions > from those reports. Maybe I was wrong.. > > Any more hints on the latter? `make allnoconfig'?
On Tue, Apr 05, 2022 at 03:49:12PM -0700, Andrew Morton wrote: > On Tue, 5 Apr 2022 18:42:43 -0400 Peter Xu <peterx@redhat.com> wrote: > > > On Tue, Apr 05, 2022 at 03:16:16PM -0700, Andrew Morton wrote: > > > On Mon, 4 Apr 2022 21:46:23 -0400 Peter Xu <peterx@redhat.com> wrote: > > > > > > > This is v8 of the series to add shmem+hugetlbfs support for userfaultfd > > > > write protection. > > > > > > Various compilation catastrophes with x86_64 allnoconfig. I poked at > > > the include ordering for a while but other things quickly became more > > > attractive ;) > > > > Sorry about that. I still don't know what's the problem, but I'll give it > > a shot soon. > > > > I think I only tried out with the new configs but not all the rest configs. > > I thought there're some bot looking after that one, from which I used to > > receive build reports. And IIRC I fixed some build issues in early versions > > from those reports. Maybe I was wrong.. > > > > Any more hints on the latter? > > `make allnoconfig'? > Ah! I thought when you mentioned "other things" you meant there're other more severe issues... :) For the allnoconfig, could you try with the attached quick fixup (upon patch "mm/uffd: PTE_MARKER_UFFD_WP")? That works for me on x86/arm, but I'm still trying out some other configs. Thanks,
On Tue, 5 Apr 2022 19:02:32 -0400 Peter Xu <peterx@redhat.com> wrote: > For the allnoconfig, could you try with the attached quick fixup (upon > patch "mm/uffd: PTE_MARKER_UFFD_WP")? Works for me, thanks.
On Mon, 4 Apr 2022 21:46:23 -0400 Peter Xu <peterx@redhat.com> wrote: > This is v8 of the series to add shmem+hugetlbfs support for userfaultfd > write protection. I think we've finished tossing this patchset around, so I plan to feed it into mm-stable later this week. A few -fixes were added: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-introduce-pte_marker-swap-entry-fix.patch https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-teach-core-mm-about-pte-markers-fix.patch https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-check-against-orig_pte-for-finish_fault-fix.patch https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-check-against-orig_pte-for-finish_fault-fix-checkpatch-fixes.patch https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-uffd-pte_marker_uffd_wp-fix.patch https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-only-drop-uffd-wp-special-pte-if-required-fix.patch https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-only-drop-uffd-wp-special-pte-if-required-fix-fix.patch https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-shmem-handle-uffd-wp-during-fork-fix.patch https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-enable-pte-markers-by-default-fix.patch
This is v8 of the series to add shmem+hugetlbfs support for userfaultfd write protection. It is based on v5.17-mmots-2022-03-31-20-40. I touched up two small details after the rebase, namely: - Let UFFDIO_REGISTER fail gracefully if CONFIG_PTE_MARKER_UFFD_WP is not set, in "mm/uffd: Enable write protection for shmem & hugetlbfs". - Tweaked the patch "mm: Enable PTE markers by default" to make sure it'll be auto-enabled on x86_64 (for real) by kconfig where proper. During testing of recent versions, I grew another unit test for uffd-wp specifically (uffd-test [0], name is not important.. though). The current vm/userfaultfd test doesn't cover the case to check what message we expect, so the simple new test can catch errors when e.g. one page was wr-protected but it was wrongly written without being noticed by the fault resolving thread, hence data corrupt. I used to only find such issues with umapsort only, and MISSING mode won't have those data loss issues. But now many of it can also be found with uffd-test [0]. I plan to port it to linux repo after this series lands. The whole tree can be found here for testing: https://github.com/xzpeter/linux/tree/uffd-wp-shmem-hugetlbfs Previous versions: RFC: https://lore.kernel.org/lkml/20210115170907.24498-1-peterx@redhat.com v1: https://lore.kernel.org/lkml/20210323004912.35132-1-peterx@redhat.com v2: https://lore.kernel.org/lkml/20210427161317.50682-1-peterx@redhat.com v3: https://lore.kernel.org/lkml/20210527201927.29586-1-peterx@redhat.com v4: https://lore.kernel.org/lkml/20210714222117.47648-1-peterx@redhat.com v5: https://lore.kernel.org/lkml/20210715201422.211004-1-peterx@redhat.com v6: https://lore.kernel.org/lkml/20211115075522.73795-1-peterx@redhat.com v7: https://lore.kernel.org/lkml/20220304051708.86193-1-peterx@redhat.com Overview ======== Userfaultfd-wp anonymous support was merged two years ago. There're quite a few applications that started to leverage this capability either to take snapshots for user-app memory, or use it for full user controled swapping. This series tries to complete the feature for uffd-wp so as to cover all the RAM-based memory types. So far uffd-wp is the only missing piece of the rest features (uffd-missing & uffd-minor mode). One major reason to do so is that anonymous pages are sometimes not satisfying the need of applications, and there're growing users of either shmem and hugetlbfs for either sharing purpose (e.g., sharing guest mem between hypervisor process and device emulation process, shmem local live migration for upgrades), or for performance on tlb hits. All these mean that if a uffd-wp app wants to switch to any of the memory types, it'll stop working. I think it's worthwhile to have the kernel to cover all these aspects. This series chose to protect pages in pte level not page level. One major reason is safety. I have no idea how we could make it safe if any of the uffd-privileged app can wr-protect a page that any other application can use. It means this app can block any process potentially for any time it wants. The other reason is that it aligns very well with not only the anonymous uffd-wp solution, but also uffd as a whole. For example, userfaultfd is implemented fundamentally based on VMAs. We set flags to VMAs showing the status of uffd tracking. For another per-page based protection solution, it'll be crossing the fundation line on VMA-based, and it could simply be too far away already from what's called userfaultfd. PTE markers =========== The patchset is based on the idea called PTE markers. It was discussed in one of the mm alignment sessions, proposed starting from v6, and this is the 2nd version of it using PTE marker idea. PTE marker is a new type of swap entry that is ony applicable to file backed memories like shmem and hugetlbfs. It's used to persist some pte-level information even if the original present ptes in pgtable are zapped. Logically pte markers can store more than uffd-wp information, but so far only one bit is used for uffd-wp purpose. When the pte marker is installed with uffd-wp bit set, it means this pte is wr-protected by uffd. It solves the problem on e.g. file-backed memory mapped ptes got zapped due to any reason (e.g. thp split, or swapped out), we can still keep the wr-protect information in the ptes. Then when the page fault triggers again, we'll know this pte is wr-protected so we can treat the pte the same as a normal uffd wr-protected pte. The extra information is encoded into the swap entry, or swp_offset to be explicit, with the swp_type being PTE_MARKER. So far uffd-wp only uses one bit out of the swap entry, the rest bits of swp_offset are still reserved for other purposes. There're two configs to enable/disable PTE markers: CONFIG_PTE_MARKER CONFIG_PTE_MARKER_UFFD_WP We can set !PTE_MARKER to completely disable all the PTE markers, along with uffd-wp support. I made two config so we can also enable PTE marker but disable uffd-wp file-backed for other purposes. At the end of current series, I'll enable CONFIG_PTE_MARKER by default, but that patch is standalone and if anyone worries about having it by default, we can also consider turn it off by dropping that oneliner patch. So far I don't see a huge risk of doing so, so I kept that patch. In most cases, PTE markers should be treated as none ptes. It is because that unlike most of the other swap entry types, there's no PFN or block offset information encoded into PTE markers but some extra well-defined bits showing the status of the pte. These bits should only be used as extra data when servicing an upcoming page fault, and then we behave as if it's a none pte. I did spend a lot of time observing all the pte_none() users this time. It is indeed a challenge because there're a lot, and I hope I didn't miss a single of them when we should take care of pte markers. Luckily, I don't think it'll need to be considered in many cases, for example: boot code, arch code (especially non-x86), kernel-only page handlings (e.g. CPA), or device driver codes when we're tackling with pure PFN mappings. I introduced pte_none_mostly() in this series when we need to handle pte markers the same as none pte, the "mostly" is the other way to write "either none pte or a pte marker". I didn't replace pte_none() to cover pte markers for below reasons: - Very rare case of pte_none() callers will handle pte markers. E.g., all the kernel pages do not require knowledge of pte markers. So we don't pollute the major use cases. - Unconditionally change pte_none() semantics could confuse people, because pte_none() existed for so long a time. - Unconditionally change pte_none() semantics could make pte_none() slower even if in many cases pte markers do not exist. - There're cases where we'd like to handle pte markers differntly from pte_none(), so a full replace is also impossible. E.g. khugepaged should still treat pte markers as normal swap ptes rather than none ptes, because pte markers will always need a fault-in to merge the marker with a valid pte. Or the smap code will need to parse PTE markers not none ptes. Patch Layout ============ Introducing PTE marker and uffd-wp bit in PTE marker: mm: Introduce PTE_MARKER swap entry mm: Teach core mm about pte markers mm: Check against orig_pte for finish_fault() mm/uffd: PTE_MARKER_UFFD_WP Adding support for shmem uffd-wp: mm/shmem: Take care of UFFDIO_COPY_MODE_WP mm/shmem: Handle uffd-wp special pte in page fault handler mm/shmem: Persist uffd-wp bit across zapping for file-backed mm/shmem: Allow uffd wr-protect none pte for file-backed mem mm/shmem: Allows file-back mem to be uffd wr-protected on thps mm/shmem: Handle uffd-wp during fork() Adding support for hugetlbfs uffd-wp: mm/hugetlb: Introduce huge pte version of uffd-wp helpers mm/hugetlb: Hook page faults for uffd write protection mm/hugetlb: Take care of UFFDIO_COPY_MODE_WP mm/hugetlb: Handle UFFDIO_WRITEPROTECT mm/hugetlb: Handle pte markers in page faults mm/hugetlb: Allow uffd wr-protect none ptes mm/hugetlb: Only drop uffd-wp special pte if required mm/hugetlb: Handle uffd-wp during fork() Misc handling on the rest mm for uffd-wp file-backed: mm/khugepaged: Don't recycle vma pgtable if uffd-wp registered mm/pagemap: Recognize uffd-wp bit for shmem/hugetlbfs Enabling of uffd-wp on file-backed memory: mm/uffd: Enable write protection for shmem & hugetlbfs mm: Enable PTE markers by default selftests/uffd: Enable uffd-wp for shmem/hugetlbfs Tests ===== - Compile test on x86_64 and aarch64 on different configs - Kernel selftests - uffd-test [0] - Umapsort [1,2] test for shmem/hugetlb, with swap on/off Please review, thanks. [0] https://github.com/xzpeter/clibs/tree/master/uffd-test [1] https://github.com/xzpeter/umap-apps/tree/peter [2] https://github.com/xzpeter/umap/tree/peter-shmem-hugetlbfs Peter Xu (23): mm: Introduce PTE_MARKER swap entry mm: Teach core mm about pte markers mm: Check against orig_pte for finish_fault() mm/uffd: PTE_MARKER_UFFD_WP mm/shmem: Take care of UFFDIO_COPY_MODE_WP mm/shmem: Handle uffd-wp special pte in page fault handler mm/shmem: Persist uffd-wp bit across zapping for file-backed mm/shmem: Allow uffd wr-protect none pte for file-backed mem mm/shmem: Allows file-back mem to be uffd wr-protected on thps mm/shmem: Handle uffd-wp during fork() mm/hugetlb: Introduce huge pte version of uffd-wp helpers mm/hugetlb: Hook page faults for uffd write protection mm/hugetlb: Take care of UFFDIO_COPY_MODE_WP mm/hugetlb: Handle UFFDIO_WRITEPROTECT mm/hugetlb: Handle pte markers in page faults mm/hugetlb: Allow uffd wr-protect none ptes mm/hugetlb: Only drop uffd-wp special pte if required mm/hugetlb: Handle uffd-wp during fork() mm/khugepaged: Don't recycle vma pgtable if uffd-wp registered mm/pagemap: Recognize uffd-wp bit for shmem/hugetlbfs mm/uffd: Enable write protection for shmem & hugetlbfs mm: Enable PTE markers by default selftests/uffd: Enable uffd-wp for shmem/hugetlbfs arch/s390/include/asm/hugetlb.h | 15 ++ fs/hugetlbfs/inode.c | 15 +- fs/proc/task_mmu.c | 7 + fs/userfaultfd.c | 31 ++-- include/asm-generic/hugetlb.h | 24 +++ include/linux/hugetlb.h | 27 ++-- include/linux/mm.h | 10 ++ include/linux/mm_inline.h | 43 +++++ include/linux/shmem_fs.h | 4 +- include/linux/swap.h | 15 +- include/linux/swapops.h | 79 +++++++++ include/linux/userfaultfd_k.h | 80 +++++++++ include/uapi/linux/userfaultfd.h | 10 +- mm/Kconfig | 17 ++ mm/filemap.c | 5 + mm/hmm.c | 2 +- mm/hugetlb.c | 183 ++++++++++++++++----- mm/khugepaged.c | 14 +- mm/memcontrol.c | 8 +- mm/memory.c | 196 ++++++++++++++++++++--- mm/mincore.c | 3 +- mm/mprotect.c | 75 ++++++++- mm/rmap.c | 8 + mm/shmem.c | 4 +- mm/userfaultfd.c | 54 +++++-- tools/testing/selftests/vm/userfaultfd.c | 4 +- 26 files changed, 807 insertions(+), 126 deletions(-)