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[184.145.104.227]) by smtp.gmail.com with ESMTPSA id v66sm3103621qkd.113.2021.04.27.09.13.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Apr 2021 09:13:19 -0700 (PDT) From: Peter Xu To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Nadav Amit , Miaohe Lin , Mike Rapoport , Andrea Arcangeli , Hugh Dickins , peterx@redhat.com, Jerome Glisse , Mike Kravetz , Jason Gunthorpe , Matthew Wilcox , Andrew Morton , Axel Rasmussen , "Kirill A . Shutemov" Subject: [PATCH v2 00/24] userfaultfd-wp: Support shmem and hugetlbfs Date: Tue, 27 Apr 2021 12:12:53 -0400 Message-Id: <20210427161317.50682-1-peterx@redhat.com> X-Mailer: git-send-email 2.26.2 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 v2 of uffd-wp shmem & hugetlbfs support, which completes uffd-wp as= a=0D kernel full feature, as it only supports anonymous before this series.=0D =0D This patchset is based mostly on tag v5.12-rc8-mmots-2021-04-21-23-08, howe= ver=0D I dropped some patches there otherwise I'll get some weird build errors. I= =0D think I should have kept most of the -mm-next materials, so hopefully when= =0D Andrew gets a new -mm tree, this series can be applied cleanly upon it. I'= ll=0D respin otherwise.=0D =0D The whole series can also be found online [1].=0D =0D The major change from v1->v2 is that I dropped the FAULT_FLAG_UFFD_WP flag = in=0D previous v1, as I think it's not needed and checking of the flag:=0D =0D vmf->flags & FAULT_FLAG_UFFD_WP=0D =0D Can be replaced safely by:=0D =0D pte_swp_uffd_wp_special(vmf->orig_pte)=0D =0D So we don't need to introduce yet another flag, and the code actually even= =0D shrinked a few more lines, which is good.=0D =0D Also per discussion with Mike, I dropped the READ emulation when a thread=0D faulted on a uffd-wp special swap pte, as I'll keep the WRITE fault as is i= n=0D this series.=0D =0D Nothing big really changed otherwise. Full changelog listed below.=0D =0D v2:=0D - Add R-bs=0D - Added patch "mm/hugetlb: Drop __unmap_hugepage_range definition from=0D hugetlb.h" as noticed/suggested by Mike Kravets=0D - Fix commit message of patch "hugetlb/userfaultfd: Only drop uffd-wp speci= al=0D pte if required" [MikeK]=0D - Removing comments for fields in zap_details since they're either incorrec= t or=0D not helping [Matthew]=0D - Rephrase commit message in patch "hugetlb/userfaultfd: Take care of=0D UFFDIO_COPY_MODE_WP" to explain better on why set dirty bit for UFFDIO_CO= PY=0D in hugetlbfs [MikeK]=0D - Don't emulate READ for uffd-wp-special on both shmem & hugetlbfs.=0D - Drop FAULT_FLAG_UFFD_WP flag, by checking vmf->orig_pte directly against= =0D pte_swp_uffd_wp_special()=0D - Fix race condition of page fault handling on uffd-wp-special [Mike]=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 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 (2): 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 mm/hugetlb: Drop __unmap_hugepage_range definition from hugetlb.h=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 (3): 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=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/LLNL/umap-apps=0D [3] https://github.com/xzpeter/umap/tree/peter-shmem-hugetlbfs=0D =0D Peter Xu (24):=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 mm/hugetlb: Drop __unmap_hugepage_range definition from hugetlb.h=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/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/dax.c | 10 +-=0D fs/hugetlbfs/inode.c | 15 +-=0D fs/proc/task_mmu.c | 14 +-=0D fs/userfaultfd.c | 39 ++--=0D include/asm-generic/hugetlb.h | 10 +=0D include/asm-generic/pgtable_uffd.h | 3 +=0D include/linux/hugetlb.h | 30 ++-=0D include/linux/mm.h | 48 ++++-=0D include/linux/mm_inline.h | 43 +++++=0D include/linux/shmem_fs.h | 5 +-=0D include/linux/swapops.h | 39 +++-=0D include/linux/userfaultfd_k.h | 47 +++++=0D include/uapi/linux/userfaultfd.h | 7 +-=0D mm/gup.c | 2 +-=0D mm/hmm.c | 2 +-=0D mm/hugetlb.c | 160 +++++++++++++---=0D mm/khugepaged.c | 14 +-=0D mm/madvise.c | 4 +-=0D mm/memcontrol.c | 2 +-=0D mm/memory.c | 226 +++++++++++++++++------=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 | 40 +++-=0D mm/swapfile.c | 2 +-=0D mm/truncate.c | 17 +-=0D mm/userfaultfd.c | 37 ++--=0D tools/testing/selftests/vm/userfaultfd.c | 9 +-=0D 33 files changed, 753 insertions(+), 187 deletions(-)=0D =0D -- =0D 2.26.2=0D =0D