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[184.144.111.238]) by smtp.gmail.com with ESMTPSA id p64sm2915206qka.114.2021.07.15.13.14.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 15 Jul 2021 13:14:25 -0700 (PDT) From: Peter Xu To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Jason Gunthorpe , Mike Kravetz , David Hildenbrand , Alistair Popple , Matthew Wilcox , "Kirill A . Shutemov" , Hugh Dickins , Tiberiu Georgescu , Andrea Arcangeli , Axel Rasmussen , Nadav Amit , Mike Rapoport , Jerome Glisse , Andrew Morton , Miaohe Lin , peterx@redhat.com Subject: [PATCH v5 00/26] userfaultfd-wp: Support shmem and hugetlbfs Date: Thu, 15 Jul 2021 16:13:56 -0400 Message-Id: <20210715201422.211004-1-peterx@redhat.com> X-Mailer: git-send-email 2.31.1 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is v5 of uffd-wp shmem & hugetlbfs support, which completes uffd-wp as= a=0D full feature. It's based on v5.14-rc1.=0D =0D I reposted the whole series majorly to trigger the syzbot tests again; sorr= y if=0D it brings a bit of noise. Please let me know if there's easier way to trig= ger=0D the syzbot test instead of reposting the whole series.=0D =0D Meanwhile, recently discussion around soft-dirty shows that soft-dirty may = have=0D similar requirement as uffd-wp on persisting the dirty information:=0D =0D https://lore.kernel.org/lkml/20210714152426.216217-1-tiberiu.georgescu@nuta= nix.com/=0D =0D Then the mechanism provided in this patchset may be suitable for soft-dirty= too.=0D =0D The whole series can also be found online [1].=0D =0D v5 changelog:=0D - Fix two issues spotted by syzbot=0D - Compile test with (1) !USERFAULTFD, (2) USERFAULTFD && !USERFAULTFD_WP=0D =0D Previous versions:=0D =0D RFC: https://lore.kernel.org/lkml/20210115170907.24498-1-peterx@redhat.com/= =0D v1: https://lore.kernel.org/lkml/20210323004912.35132-1-peterx@redhat.com/= =0D v2: https://lore.kernel.org/lkml/20210427161317.50682-1-peterx@redhat.com/= =0D v3: https://lore.kernel.org/lkml/20210527201927.29586-1-peterx@redhat.com/= =0D v4: https://lore.kernel.org/lkml/20210714222117.47648-1-peterx@redhat.com/= =0D =0D About Swap Special PTE=0D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=0D =0D In short, the so-called "swap special pte" in this patchset is a new type o= f=0D pte that doesn't exist in the past, but it got used initially in this serie= s in=0D file-backed memories. It is used to persist information even if the ptes g= ot=0D dropped meanwhile when the page cache still existed. For example, when=0D splitting a file-backed huge pmd, we could be simply dropping the pmd entry= =0D then wait until another fault coming. It's okay in the past since all=0D information in the pte can be retained from the page cache when the next pa= ge=0D fault triggers. However in this case, uffd-wp is per-pte information which= =0D cannot be kept in page cache, so that information needs to be maintained=0D somehow still in the pgtable entry, even if the pgtable entry is going to b= e=0D dropped. Here instead of replacing with a none entry, we used the "swap=0D special pte". Then when the next page fault triggers, we can observe orig_= pte=0D to retain this information.=0D =0D I'm copy-pasting some commit message from the patch "mm/swap: Introduce the= =0D idea of special swap ptes", where it tried to explain this pte in another a= ngle:=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): Shmem support, this is where the special swap pte is introduced.= =0D Some zap rework is needed within the process:=0D =0D mm/shmem: Unconditionally set pte dirty in mfill_atomic_install_pte=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 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 (2): Hugetlb supportdisable huge pmd sharing for uffd-wp patches have = been=0D merged. The rest is the changes required to teach hugetlbfs understand the= =0D special swap pte too that introduced with the uffd-wp change:=0D =0D mm/hugetlb: Drop __unmap_hugepage_range definition from hugetlb.h=0D mm/hugetlb: Introduce huge pte version of uffd-wp helpers=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 mm/hugetlb: Introduce huge version of special swap pte helpers=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 (3): Enable both features in code and test (plus pagemap support)=0D =0D mm/pagemap: Recognize uffd-wp bit for shmem/hugetlbfs=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=0D =0D I've tested it using either userfaultfd kselftest program, but also with=0D umapsort [2] which should be even stricter. Tested page swapping in/out du= ring=0D umapsort.=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 [1] https://github.com/xzpeter/linux/tree/uffd-wp-shmem-hugetlbfs=0D [2] https://github.com/xzpeter/umap-apps/tree/peter=0D [3] https://github.com/xzpeter/umap/tree/peter-shmem-hugetlbfs=0D [4] https://github.com/xzpeter/umap-apps/commit/b0c2c7b1cd9dcb6835e7c59d02e= ce1f6b7f1ea01=0D =0D Peter Xu (26):=0D mm/shmem: Unconditionally set pte dirty in mfill_atomic_install_pte=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 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 mm/hugetlb: Drop __unmap_hugepage_range definition from hugetlb.h=0D mm/hugetlb: Introduce huge pte version of uffd-wp helpers=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 mm/hugetlb: Introduce huge version of special swap pte helpers=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 mm/pagemap: Recognize uffd-wp bit for shmem/hugetlbfs=0D mm/userfaultfd: Enable write protection for shmem & hugetlbfs=0D userfaultfd/selftests: Enable uffd-wp for shmem/hugetlbfs=0D =0D arch/arm64/kernel/mte.c | 2 +-=0D arch/x86/include/asm/pgtable.h | 28 +++=0D fs/hugetlbfs/inode.c | 15 +-=0D fs/proc/task_mmu.c | 21 +-=0D fs/userfaultfd.c | 41 ++--=0D include/asm-generic/hugetlb.h | 15 ++=0D include/asm-generic/pgtable_uffd.h | 3 +=0D include/linux/hugetlb.h | 30 ++-=0D include/linux/mm.h | 44 +++-=0D include/linux/mm_inline.h | 42 ++++=0D include/linux/shmem_fs.h | 4 +-=0D include/linux/swapops.h | 39 +++-=0D include/linux/userfaultfd_k.h | 54 +++++=0D include/uapi/linux/userfaultfd.h | 10 +-=0D mm/gup.c | 2 +-=0D mm/hmm.c | 2 +-=0D mm/hugetlb.c | 164 ++++++++++++---=0D mm/khugepaged.c | 11 +-=0D mm/madvise.c | 4 +-=0D mm/memcontrol.c | 2 +-=0D mm/memory.c | 244 +++++++++++++++++------=0D mm/migrate.c | 4 +-=0D mm/mincore.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 | 5 +-=0D mm/swapfile.c | 2 +-=0D mm/userfaultfd.c | 73 +++++--=0D tools/testing/selftests/vm/userfaultfd.c | 9 +-=0D 31 files changed, 763 insertions(+), 188 deletions(-)=0D =0D -- =0D 2.31.1=0D =0D