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Shutemov" , Hugh Dickins , Axel Rasmussen , Matthew Wilcox , Andrew Morton , Andrea Arcangeli , Nadav Amit Subject: [PATCH RFC 00/30] userfaultfd-wp: Support shmem and hugetlbfs Date: Fri, 15 Jan 2021 12:08:37 -0500 Message-Id: <20210115170907.24498-1-peterx@redhat.com> X-Mailer: git-send-email 2.26.2 MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=peterx@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: This is a RFC series to support userfaultfd upon shmem and hugetlbfs.=0D =0D PS. Note that there's a known issue [0] with tlb against uffd-wp/soft-dirty= in=0D general and Nadav is working on it. It may or may not directly affect=0D shmem/hugetlbfs since there're no COW on shared mappings normally. Private= =0D shmem could hit, but still that's another problem to solve in general, and = this=0D RFC is majorly to see whether there's any objection on the concept of the i= dea=0D specific to uffd-wp on shmem/hugetlbfs.=0D =0D The whole series can also be found online [1].=0D =0D The major comment I'd like to get is on the new idea of swap special pte. = That=0D comes from suggestions from both Hugh and Andrea and I appreciated a lot fo= r=0D those discussions.=0D =0D In short, it's a new type of pte that doesn't exist in the past, while used= in=0D file-backed memories to persist information across ptes being erased (but t= he=0D page cache could still exist, for example, so in the next page fault we can= =0D reload the page cache with that specific information when necessary).=0D =0D I'm copy-pasting some commit message from the patch "mm/swap: Introduce the= =0D idea of special swap ptes", where uffd-wp becomes the first user of it:=0D =0D We used to have special swap entries, like migration entries, hw-poison= =0D entries, device private entries, etc.=0D =0D Those "special swap entries" reside in the range that they need to be a= t least=0D swap entries first, and their types are decided by swp_type(entry).=0D =0D This patch introduces another idea called "special swap ptes".=0D =0D It's very easy to get confused against "special swap entries", but a sp= eical=0D swap pte should never contain a swap entry at all. It means, it's ille= gal to=0D call pte_to_swp_entry() upon a special swap pte.=0D =0D Make the uffd-wp special pte to be the first special swap pte.=0D =0D Before this patch, is_swap_pte()=3D=3Dtrue means one of the below:=0D =0D (a.1) The pte has a normal swap entry (non_swap_entry()=3D=3Dfalse).= For=0D example, when an anonymous page got swapped out.=0D =0D (a.2) The pte has a special swap entry (non_swap_entry()=3D=3Dtrue).= For=0D example, a migration entry, a hw-poison entry, etc.=0D =0D After this patch, is_swap_pte()=3D=3Dtrue means one of the below, where= case (b) is=0D added:=0D =0D (a) The pte contains a swap entry.=0D =0D (a.1) The pte has a normal swap entry (non_swap_entry()=3D=3Dfalse).= For=0D example, when an anonymous page got swapped out.=0D =0D (a.2) The pte has a special swap entry (non_swap_entry()=3D=3Dtrue).= For=0D example, a migration entry, a hw-poison entry, etc.=0D =0D (b) The pte does not contain a swap entry at all (so it cannot be pass= ed=0D into pte_to_swp_entry()). For example, uffd-wp special swap pte.= =0D =0D Hugetlbfs needs similar thing because it's also file-backed. I directly re= used=0D the same special pte there, though the shmem/hugetlb change on supporting t= his=0D new pte is different since they don't share code path a lot.=0D =0D Patch layout=0D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=0D =0D Part (1): some fixes that I observed when working on this; feel free to ski= p=0D them for now becuase I think they're corner cases and irrelevant of the maj= or=0D change:=0D =0D mm/thp: Simplify copying of huge zero page pmd when fork=0D mm/userfaultfd: Fix uffd-wp special cases for fork()=0D mm/userfaultfd: Fix a few thp pmd missing uffd-wp bit=0D =0D Part (2): Shmem support, this is where the special swap pte is introduced.= =0D Some zap rework is needed within the process:=0D =0D shmem/userfaultfd: Take care of UFFDIO_COPY_MODE_WP=0D mm: Clear vmf->pte after pte_unmap_same() returns=0D mm/userfaultfd: Introduce special pte for unmapped file-backed mem=0D mm/swap: Introduce the idea of special swap ptes=0D shmem/userfaultfd: Handle uffd-wp special pte in page fault handler=0D mm: Drop first_index/last_index in zap_details=0D mm: Introduce zap_details.zap_flags=0D mm: Introduce ZAP_FLAG_SKIP_SWAP=0D mm: Pass zap_flags into unmap_mapping_pages()=0D shmem/userfaultfd: Persist uffd-wp bit across zapping for file-backed=0D shmem/userfaultfd: Allow wr-protect none pte for file-backed mem=0D shmem/userfaultfd: Allows file-back mem to be uffd wr-protected on thps= =0D shmem/userfaultfd: Handle the left-overed special swap ptes=0D shmem/userfaultfd: Pass over uffd-wp special swap pte when fork()=0D =0D Part (3): Hugetlb support, we need to disable huge pmd sharing for uffd-wp= =0D because not compatible just like uffd minor mode. The rest is the changes= =0D required to teach hugetlbfs understand the special swap pte too that introd= uced=0D with the uffd-wp change:=0D =0D hugetlb/userfaultfd: Hook page faults for uffd write protection=0D hugetlb/userfaultfd: Take care of UFFDIO_COPY_MODE_WP=0D hugetlb/userfaultfd: Handle UFFDIO_WRITEPROTECT=0D hugetlb: Pass vma into huge_pte_alloc()=0D hugetlb/userfaultfd: Forbid huge pmd sharing when uffd enabled=0D mm/hugetlb: Introduce huge version of special swap pte helpers=0D mm/hugetlb: Move flush_hugetlb_tlb_range() into hugetlb.h=0D hugetlb/userfaultfd: Unshare all pmds for hugetlbfs when register wp=0D hugetlb/userfaultfd: Handle uffd-wp special pte in hugetlb pf handler=0D hugetlb/userfaultfd: Allow wr-protect none ptes=0D hugetlb/userfaultfd: Only drop uffd-wp special pte if required=0D =0D Part (4): Enable both features in code and test=0D =0D userfaultfd: Enable write protection for shmem & hugetlbfs=0D userfaultfd/selftests: Enable uffd-wp for shmem/hugetlbfs=0D =0D Tests=0D =3D=3D=3D=3D=3D=3D=3D=3D=3D=0D =0D I've tested it using either userfaultfd kselftest program, but also with=0D umapsort [2] which should be even stricter. No complicated mm setup is tes= ted=0D yet besides page swapping in/out, but in all cases we need to have more tes= ts=0D when it becomes non-RFC.=0D =0D If anyone would like to try umapsort, need to use an extremely hacked versi= on=0D of umap library [3], because by default umap only supports anonymous. So t= o=0D test it we need to build [3] then [2].=0D =0D Any comment would be greatly welcomed. Thanks,=0D =0D [0] https://lore.kernel.org/lkml/20201225092529.3228466-1-namit@vmware.com/= =0D [1] https://github.com/xzpeter/linux/tree/uffd-wp-shmem-hugetlbfs=0D [2] https://github.com/LLNL/umap-apps=0D [3] https://github.com/xzpeter/umap/tree/peter-shmem-hugetlbfs=0D =0D Peter Xu (30):=0D mm/thp: Simplify copying of huge zero page pmd when fork=0D mm/userfaultfd: Fix uffd-wp special cases for fork()=0D mm/userfaultfd: Fix a few thp pmd missing uffd-wp bit=0D shmem/userfaultfd: Take care of UFFDIO_COPY_MODE_WP=0D mm: Clear vmf->pte after pte_unmap_same() returns=0D mm/userfaultfd: Introduce special pte for unmapped file-backed mem=0D mm/swap: Introduce the idea of special swap ptes=0D shmem/userfaultfd: Handle uffd-wp special pte in page fault handler=0D mm: Drop first_index/last_index in zap_details=0D mm: Introduce zap_details.zap_flags=0D mm: Introduce ZAP_FLAG_SKIP_SWAP=0D mm: Pass zap_flags into unmap_mapping_pages()=0D shmem/userfaultfd: Persist uffd-wp bit across zapping for file-backed=0D shmem/userfaultfd: Allow wr-protect none pte for file-backed mem=0D shmem/userfaultfd: Allows file-back mem to be uffd wr-protected on=0D thps=0D shmem/userfaultfd: Handle the left-overed special swap ptes=0D shmem/userfaultfd: Pass over uffd-wp special swap pte when fork()=0D hugetlb/userfaultfd: Hook page faults for uffd write protection=0D hugetlb/userfaultfd: Take care of UFFDIO_COPY_MODE_WP=0D hugetlb/userfaultfd: Handle UFFDIO_WRITEPROTECT=0D hugetlb: Pass vma into huge_pte_alloc()=0D hugetlb/userfaultfd: Forbid huge pmd sharing when uffd enabled=0D mm/hugetlb: Introduce huge version of special swap pte helpers=0D mm/hugetlb: Move flush_hugetlb_tlb_range() into hugetlb.h=0D hugetlb/userfaultfd: Unshare all pmds for hugetlbfs when register wp=0D hugetlb/userfaultfd: Handle uffd-wp special pte in hugetlb pf handler=0D hugetlb/userfaultfd: Allow wr-protect none ptes=0D hugetlb/userfaultfd: Only drop uffd-wp special pte if required=0D userfaultfd: Enable write protection for shmem & hugetlbfs=0D userfaultfd/selftests: Enable uffd-wp for shmem/hugetlbfs=0D =0D arch/arm64/mm/hugetlbpage.c | 5 +-=0D arch/ia64/mm/hugetlbpage.c | 3 +-=0D arch/mips/mm/hugetlbpage.c | 4 +-=0D arch/parisc/mm/hugetlbpage.c | 2 +-=0D arch/powerpc/mm/hugetlbpage.c | 3 +-=0D arch/s390/mm/hugetlbpage.c | 2 +-=0D arch/sh/mm/hugetlbpage.c | 2 +-=0D arch/sparc/mm/hugetlbpage.c | 2 +-=0D arch/x86/include/asm/pgtable.h | 28 +++=0D fs/dax.c | 10 +-=0D fs/hugetlbfs/inode.c | 15 +-=0D fs/proc/task_mmu.c | 14 +-=0D fs/userfaultfd.c | 80 +++++--=0D include/asm-generic/hugetlb.h | 10 +=0D include/asm-generic/pgtable_uffd.h | 3 +=0D include/linux/huge_mm.h | 3 +-=0D include/linux/hugetlb.h | 47 +++-=0D include/linux/mm.h | 50 +++-=0D include/linux/mm_inline.h | 43 ++++=0D include/linux/mmu_notifier.h | 1 +=0D include/linux/shmem_fs.h | 5 +-=0D include/linux/swapops.h | 41 +++-=0D include/linux/userfaultfd_k.h | 37 +++=0D include/uapi/linux/userfaultfd.h | 3 +-=0D mm/huge_memory.c | 36 ++-=0D mm/hugetlb.c | 174 +++++++++++---=0D mm/khugepaged.c | 14 +-=0D mm/memcontrol.c | 2 +-=0D mm/memory.c | 277 ++++++++++++++++++-----=0D mm/migrate.c | 2 +-=0D mm/mprotect.c | 63 +++++-=0D mm/mremap.c | 2 +-=0D mm/page_vma_mapped.c | 6 +-=0D mm/rmap.c | 8 +=0D mm/shmem.c | 39 +++-=0D mm/truncate.c | 17 +-=0D mm/userfaultfd.c | 37 +--=0D tools/testing/selftests/vm/userfaultfd.c | 14 +-=0D 38 files changed, 881 insertions(+), 223 deletions(-)=0D =0D --=20=0D 2.26.2=0D =0D