Patch series "Implement IOCTL to get and optionally clear info about PTEs", v33. *Motivation* The real motivation for adding PAGEMAP_SCAN IOCTL is to emulate Windows GetWriteWatch() and ResetWriteWatch() syscalls [1]. The GetWriteWatch() retrieves the addresses of the pages that are written to in a region of virtual memory. This syscall is used in Windows applications and games etc. This syscall is being emulated in pretty slow manner in userspace. Our purpose is to enhance the kernel such that we translate it efficiently in a better way. Currently some out of tree hack patches are being used to efficiently emulate it in some kernels. We intend to replace those with these patches. So the whole gaming on Linux can effectively get benefit from this. It means there would be tons of users of this code. CRIU use case [2] was mentioned by Andrei and Danylo: > Use cases for migrating sparse VMAs are binaries sanitized with ASAN, > MSAN or TSAN [3]. All of these sanitizers produce sparse mappings of > shadow memory [4]. Being able to migrate such binaries allows to highly > reduce the amount of work needed to identify and fix post-migration > crashes, which happen constantly. Andrei defines the following uses of this code: * it is more granular and allows us to track changed pages more effectively. The current interface can clear dirty bits for the entire process only. In addition, reading info about pages is a separate operation. It means we must freeze the process to read information about all its pages, reset dirty bits, only then we can start dumping pages. The information about pages becomes more and more outdated, while we are processing pages. The new interface solves both these downsides. First, it allows us to read pte bits and clear the soft-dirty bit atomically. It means that CRIU will not need to freeze processes to pre-dump their memory. Second, it clears soft-dirty bits for a specified region of memory. It means CRIU will have actual info about pages to the moment of dumping them. * The new interface has to be much faster because basic page filtering is happening in the kernel. With the old interface, we have to read pagemap for each page. *Implementation Evolution (Short Summary)* From the definition of GetWriteWatch(), we feel like kernel's soft-dirty feature can be used under the hood with some additions like: * reset soft-dirty flag for only a specific region of memory instead of clearing the flag for the entire process * get and clear soft-dirty flag for a specific region atomically So we decided to use ioctl on pagemap file to read or/and reset soft-dirty flag. But using soft-dirty flag, sometimes we get extra pages which weren't even written. They had become soft-dirty because of VMA merging and VM_SOFTDIRTY flag. This breaks the definition of GetWriteWatch(). We were able to by-pass this short coming by ignoring VM_SOFTDIRTY until David reported that mprotect etc messes up the soft-dirty flag while ignoring VM_SOFTDIRTY [5]. This wasn't happening until [6] got introduced. We discussed if we can revert these patches. But we could not reach to any conclusion. So at this point, I made couple of tries to solve this whole VM_SOFTDIRTY issue by correcting the soft-dirty implementation: * [7] Correct the bug fixed wrongly back in 2014. It had potential to cause regression. We left it behind. * [8] Keep a list of soft-dirty part of a VMA across splits and merges. I got the reply don't increase the size of the VMA by 8 bytes. At this point, we left soft-dirty considering it is too much delicate and userfaultfd [9] seemed like the only way forward. From there onward, we have been basing soft-dirty emulation on userfaultfd wp feature where kernel resolves the faults itself when WP_ASYNC feature is used. It was straight forward to add WP_ASYNC feature in userfautlfd. Now we get only those pages dirty or written-to which are really written in reality. (PS There is another WP_UNPOPULATED userfautfd feature is required which is needed to avoid pre-faulting memory before write-protecting [9].) All the different masks were added on the request of CRIU devs to create interface more generic and better. [1] https://learn.microsoft.com/en-us/windows/win32/api/memoryapi/nf-memoryapi-getwritewatch [2] https://lore.kernel.org/all/20221014134802.1361436-1-mdanylo@google.com [3] https://github.com/google/sanitizers [4] https://github.com/google/sanitizers/wiki/AddressSanitizerAlgorithm#64-bit [5] https://lore.kernel.org/all/bfcae708-db21-04b4-0bbe-712badd03071@redhat.com [6] https://lore.kernel.org/all/20220725142048.30450-1-peterx@redhat.com/ [7] https://lore.kernel.org/all/20221122115007.2787017-1-usama.anjum@collabora.com [8] https://lore.kernel.org/all/20221220162606.1595355-1-usama.anjum@collabora.com [9] https://lore.kernel.org/all/20230306213925.617814-1-peterx@redhat.com [10] https://lore.kernel.org/all/20230125144529.1630917-1-mdanylo@google.com This patch (of 6): Add a new userfaultfd-wp feature UFFD_FEATURE_WP_ASYNC, that allows userfaultfd wr-protect faults to be resolved by the kernel directly. It can be used like a high accuracy version of soft-dirty, without vma modifications during tracking, and also with ranged support by default rather than for a whole mm when reset the protections due to existence of ioctl(UFFDIO_WRITEPROTECT). Several goals of such a dirty tracking interface: 1. All types of memory should be supported and tracable. This is nature for soft-dirty but should mention when the context is userfaultfd, because it used to only support anon/shmem/hugetlb. The problem is for a dirty tracking purpose these three types may not be enough, and it's legal to track anything e.g. any page cache writes from mmap. 2. Protections can be applied to partial of a memory range, without vma split/merge fuss. The hope is that the tracking itself should not affect any vma layout change. It also helps when reset happens because the reset will not need mmap write lock which can block the tracee. 3. Accuracy needs to be maintained. This means we need pte markers to work on any type of VMA. One could question that, the whole concept of async dirty tracking is not really close to fundamentally what userfaultfd used to be: it's not "a fault to be serviced by userspace" anymore. However, using userfaultfd-wp here as a framework is convenient for us in at least: 1. VM_UFFD_WP vma flag, which has a very good name to suite something like this, so we don't need VM_YET_ANOTHER_SOFT_DIRTY. Just use a new feature bit to identify from a sync version of uffd-wp registration. 2. PTE markers logic can be leveraged across the whole kernel to maintain the uffd-wp bit as long as an arch supports, this also applies to this case where uffd-wp bit will be a hint to dirty information and it will not go lost easily (e.g. when some page cache ptes got zapped). 3. Reuse ioctl(UFFDIO_WRITEPROTECT) interface for either starting or resetting a range of memory, while there's no counterpart in the old soft-dirty world, hence if this is wanted in a new design we'll need a new interface otherwise. We can somehow understand that commonality because uffd-wp was fundamentally a similar idea of write-protecting pages just like soft-dirty. This implementation allows WP_ASYNC to imply WP_UNPOPULATED, because so far WP_ASYNC seems to not usable if without WP_UNPOPULATE. This also gives us chance to modify impl of WP_ASYNC just in case it could be not depending on WP_UNPOPULATED anymore in the future kernels. It's also fine to imply that because both features will rely on PTE_MARKER_UFFD_WP config option, so they'll show up together (or both missing) in an UFFDIO_API probe. vma_can_userfault() now allows any VMA if the userfaultfd registration is only about async uffd-wp. So we can track dirty for all kinds of memory including generic file systems (like XFS, EXT4 or BTRFS). One trick worth mention in do_wp_page() is that we need to manually update vmf->orig_pte here because it can be used later with a pte_same() check - this path always has FAULT_FLAG_ORIG_PTE_VALID set in the flags. The major defect of this approach of dirty tracking is we need to populate the pgtables when tracking starts. Soft-dirty doesn't do it like that. It's unwanted in the case where the range of memory to track is huge and unpopulated (e.g., tracking updates on a 10G file with mmap() on top, without having any page cache installed yet). One way to improve this is to allow pte markers exist for larger than PTE level for PMD+. That will not change the interface if to implemented, so we can leave that for later. Link: https://lkml.kernel.org/r/20230821141518.870589-1-usama.anjum@collabora.com Link: https://lkml.kernel.org/r/20230821141518.870589-2-usama.anjum@collabora.com Signed-off-by: Peter Xu <peterx@redhat.com> Co-developed-by: Muhammad Usama Anjum <usama.anjum@collabora.com> Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com> Cc: Alex Sierra <alex.sierra@amd.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Andrei Vagin <avagin@gmail.com> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: Christian Brauner <brauner@kernel.org> Cc: Cyrill Gorcunov <gorcunov@gmail.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: David Hildenbrand <david@redhat.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Gustavo A. R. Silva <gustavoars@kernel.org> Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Miroslaw <emmir@google.com> Cc: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Nadav Amit <namit@vmware.com> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Cc: Paul Gofman <pgofman@codeweavers.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Yang Shi <shy828301@gmail.com> Cc: Yun Zhou <yun.zhou@windriver.com> Cc: Michał Mirosław <mirq-linux@rere.qmqm.pl> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
359 lines
11 KiB
C
359 lines
11 KiB
C
/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
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/*
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* include/linux/userfaultfd.h
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*
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* Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
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* Copyright (C) 2015 Red Hat, Inc.
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*
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*/
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#ifndef _LINUX_USERFAULTFD_H
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#define _LINUX_USERFAULTFD_H
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#include <linux/types.h>
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/* ioctls for /dev/userfaultfd */
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#define USERFAULTFD_IOC 0xAA
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#define USERFAULTFD_IOC_NEW _IO(USERFAULTFD_IOC, 0x00)
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/*
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* If the UFFDIO_API is upgraded someday, the UFFDIO_UNREGISTER and
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* UFFDIO_WAKE ioctls should be defined as _IOW and not as _IOR. In
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* userfaultfd.h we assumed the kernel was reading (instead _IOC_READ
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* means the userland is reading).
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*/
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#define UFFD_API ((__u64)0xAA)
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#define UFFD_API_REGISTER_MODES (UFFDIO_REGISTER_MODE_MISSING | \
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UFFDIO_REGISTER_MODE_WP | \
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UFFDIO_REGISTER_MODE_MINOR)
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#define UFFD_API_FEATURES (UFFD_FEATURE_PAGEFAULT_FLAG_WP | \
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UFFD_FEATURE_EVENT_FORK | \
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UFFD_FEATURE_EVENT_REMAP | \
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UFFD_FEATURE_EVENT_REMOVE | \
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UFFD_FEATURE_EVENT_UNMAP | \
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UFFD_FEATURE_MISSING_HUGETLBFS | \
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UFFD_FEATURE_MISSING_SHMEM | \
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UFFD_FEATURE_SIGBUS | \
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UFFD_FEATURE_THREAD_ID | \
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UFFD_FEATURE_MINOR_HUGETLBFS | \
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UFFD_FEATURE_MINOR_SHMEM | \
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UFFD_FEATURE_EXACT_ADDRESS | \
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UFFD_FEATURE_WP_HUGETLBFS_SHMEM | \
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UFFD_FEATURE_WP_UNPOPULATED | \
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UFFD_FEATURE_POISON | \
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UFFD_FEATURE_WP_ASYNC)
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#define UFFD_API_IOCTLS \
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((__u64)1 << _UFFDIO_REGISTER | \
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(__u64)1 << _UFFDIO_UNREGISTER | \
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(__u64)1 << _UFFDIO_API)
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#define UFFD_API_RANGE_IOCTLS \
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((__u64)1 << _UFFDIO_WAKE | \
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(__u64)1 << _UFFDIO_COPY | \
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(__u64)1 << _UFFDIO_ZEROPAGE | \
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(__u64)1 << _UFFDIO_WRITEPROTECT | \
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(__u64)1 << _UFFDIO_CONTINUE | \
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(__u64)1 << _UFFDIO_POISON)
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#define UFFD_API_RANGE_IOCTLS_BASIC \
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((__u64)1 << _UFFDIO_WAKE | \
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(__u64)1 << _UFFDIO_COPY | \
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(__u64)1 << _UFFDIO_WRITEPROTECT | \
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(__u64)1 << _UFFDIO_CONTINUE | \
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(__u64)1 << _UFFDIO_POISON)
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/*
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* Valid ioctl command number range with this API is from 0x00 to
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* 0x3F. UFFDIO_API is the fixed number, everything else can be
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* changed by implementing a different UFFD_API. If sticking to the
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* same UFFD_API more ioctl can be added and userland will be aware of
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* which ioctl the running kernel implements through the ioctl command
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* bitmask written by the UFFDIO_API.
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*/
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#define _UFFDIO_REGISTER (0x00)
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#define _UFFDIO_UNREGISTER (0x01)
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#define _UFFDIO_WAKE (0x02)
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#define _UFFDIO_COPY (0x03)
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#define _UFFDIO_ZEROPAGE (0x04)
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#define _UFFDIO_WRITEPROTECT (0x06)
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#define _UFFDIO_CONTINUE (0x07)
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#define _UFFDIO_POISON (0x08)
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#define _UFFDIO_API (0x3F)
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/* userfaultfd ioctl ids */
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#define UFFDIO 0xAA
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#define UFFDIO_API _IOWR(UFFDIO, _UFFDIO_API, \
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struct uffdio_api)
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#define UFFDIO_REGISTER _IOWR(UFFDIO, _UFFDIO_REGISTER, \
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struct uffdio_register)
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#define UFFDIO_UNREGISTER _IOR(UFFDIO, _UFFDIO_UNREGISTER, \
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struct uffdio_range)
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#define UFFDIO_WAKE _IOR(UFFDIO, _UFFDIO_WAKE, \
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struct uffdio_range)
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#define UFFDIO_COPY _IOWR(UFFDIO, _UFFDIO_COPY, \
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struct uffdio_copy)
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#define UFFDIO_ZEROPAGE _IOWR(UFFDIO, _UFFDIO_ZEROPAGE, \
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struct uffdio_zeropage)
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#define UFFDIO_WRITEPROTECT _IOWR(UFFDIO, _UFFDIO_WRITEPROTECT, \
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struct uffdio_writeprotect)
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#define UFFDIO_CONTINUE _IOWR(UFFDIO, _UFFDIO_CONTINUE, \
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struct uffdio_continue)
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#define UFFDIO_POISON _IOWR(UFFDIO, _UFFDIO_POISON, \
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struct uffdio_poison)
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/* read() structure */
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struct uffd_msg {
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__u8 event;
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__u8 reserved1;
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__u16 reserved2;
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__u32 reserved3;
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union {
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struct {
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__u64 flags;
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__u64 address;
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union {
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__u32 ptid;
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} feat;
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} pagefault;
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struct {
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__u32 ufd;
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} fork;
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struct {
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__u64 from;
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__u64 to;
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__u64 len;
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} remap;
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struct {
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__u64 start;
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__u64 end;
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} remove;
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struct {
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/* unused reserved fields */
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__u64 reserved1;
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__u64 reserved2;
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__u64 reserved3;
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} reserved;
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} arg;
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} __packed;
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/*
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* Start at 0x12 and not at 0 to be more strict against bugs.
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*/
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#define UFFD_EVENT_PAGEFAULT 0x12
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#define UFFD_EVENT_FORK 0x13
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#define UFFD_EVENT_REMAP 0x14
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#define UFFD_EVENT_REMOVE 0x15
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#define UFFD_EVENT_UNMAP 0x16
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/* flags for UFFD_EVENT_PAGEFAULT */
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#define UFFD_PAGEFAULT_FLAG_WRITE (1<<0) /* If this was a write fault */
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#define UFFD_PAGEFAULT_FLAG_WP (1<<1) /* If reason is VM_UFFD_WP */
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#define UFFD_PAGEFAULT_FLAG_MINOR (1<<2) /* If reason is VM_UFFD_MINOR */
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struct uffdio_api {
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/* userland asks for an API number and the features to enable */
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__u64 api;
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/*
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* Kernel answers below with the all available features for
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* the API, this notifies userland of which events and/or
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* which flags for each event are enabled in the current
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* kernel.
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*
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* Note: UFFD_EVENT_PAGEFAULT and UFFD_PAGEFAULT_FLAG_WRITE
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* are to be considered implicitly always enabled in all kernels as
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* long as the uffdio_api.api requested matches UFFD_API.
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*
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* UFFD_FEATURE_MISSING_HUGETLBFS means an UFFDIO_REGISTER
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* with UFFDIO_REGISTER_MODE_MISSING mode will succeed on
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* hugetlbfs virtual memory ranges. Adding or not adding
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* UFFD_FEATURE_MISSING_HUGETLBFS to uffdio_api.features has
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* no real functional effect after UFFDIO_API returns, but
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* it's only useful for an initial feature set probe at
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* UFFDIO_API time. There are two ways to use it:
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*
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* 1) by adding UFFD_FEATURE_MISSING_HUGETLBFS to the
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* uffdio_api.features before calling UFFDIO_API, an error
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* will be returned by UFFDIO_API on a kernel without
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* hugetlbfs missing support
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*
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* 2) the UFFD_FEATURE_MISSING_HUGETLBFS can not be added in
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* uffdio_api.features and instead it will be set by the
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* kernel in the uffdio_api.features if the kernel supports
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* it, so userland can later check if the feature flag is
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* present in uffdio_api.features after UFFDIO_API
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* succeeded.
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*
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* UFFD_FEATURE_MISSING_SHMEM works the same as
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* UFFD_FEATURE_MISSING_HUGETLBFS, but it applies to shmem
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* (i.e. tmpfs and other shmem based APIs).
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*
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* UFFD_FEATURE_SIGBUS feature means no page-fault
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* (UFFD_EVENT_PAGEFAULT) event will be delivered, instead
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* a SIGBUS signal will be sent to the faulting process.
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*
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* UFFD_FEATURE_THREAD_ID pid of the page faulted task_struct will
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* be returned, if feature is not requested 0 will be returned.
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*
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* UFFD_FEATURE_MINOR_HUGETLBFS indicates that minor faults
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* can be intercepted (via REGISTER_MODE_MINOR) for
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* hugetlbfs-backed pages.
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*
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* UFFD_FEATURE_MINOR_SHMEM indicates the same support as
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* UFFD_FEATURE_MINOR_HUGETLBFS, but for shmem-backed pages instead.
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*
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* UFFD_FEATURE_EXACT_ADDRESS indicates that the exact address of page
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* faults would be provided and the offset within the page would not be
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* masked.
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*
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* UFFD_FEATURE_WP_HUGETLBFS_SHMEM indicates that userfaultfd
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* write-protection mode is supported on both shmem and hugetlbfs.
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*
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* UFFD_FEATURE_WP_UNPOPULATED indicates that userfaultfd
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* write-protection mode will always apply to unpopulated pages
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* (i.e. empty ptes). This will be the default behavior for shmem
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* & hugetlbfs, so this flag only affects anonymous memory behavior
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* when userfault write-protection mode is registered.
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*
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* UFFD_FEATURE_WP_ASYNC indicates that userfaultfd write-protection
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* asynchronous mode is supported in which the write fault is
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* automatically resolved and write-protection is un-set.
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* It implies UFFD_FEATURE_WP_UNPOPULATED.
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*/
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#define UFFD_FEATURE_PAGEFAULT_FLAG_WP (1<<0)
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#define UFFD_FEATURE_EVENT_FORK (1<<1)
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#define UFFD_FEATURE_EVENT_REMAP (1<<2)
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#define UFFD_FEATURE_EVENT_REMOVE (1<<3)
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#define UFFD_FEATURE_MISSING_HUGETLBFS (1<<4)
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#define UFFD_FEATURE_MISSING_SHMEM (1<<5)
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#define UFFD_FEATURE_EVENT_UNMAP (1<<6)
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#define UFFD_FEATURE_SIGBUS (1<<7)
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#define UFFD_FEATURE_THREAD_ID (1<<8)
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#define UFFD_FEATURE_MINOR_HUGETLBFS (1<<9)
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#define UFFD_FEATURE_MINOR_SHMEM (1<<10)
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#define UFFD_FEATURE_EXACT_ADDRESS (1<<11)
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#define UFFD_FEATURE_WP_HUGETLBFS_SHMEM (1<<12)
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#define UFFD_FEATURE_WP_UNPOPULATED (1<<13)
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#define UFFD_FEATURE_POISON (1<<14)
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#define UFFD_FEATURE_WP_ASYNC (1<<15)
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__u64 features;
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__u64 ioctls;
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};
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struct uffdio_range {
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__u64 start;
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__u64 len;
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};
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struct uffdio_register {
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struct uffdio_range range;
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#define UFFDIO_REGISTER_MODE_MISSING ((__u64)1<<0)
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#define UFFDIO_REGISTER_MODE_WP ((__u64)1<<1)
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#define UFFDIO_REGISTER_MODE_MINOR ((__u64)1<<2)
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__u64 mode;
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/*
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* kernel answers which ioctl commands are available for the
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* range, keep at the end as the last 8 bytes aren't read.
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*/
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__u64 ioctls;
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};
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struct uffdio_copy {
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__u64 dst;
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__u64 src;
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__u64 len;
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#define UFFDIO_COPY_MODE_DONTWAKE ((__u64)1<<0)
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/*
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* UFFDIO_COPY_MODE_WP will map the page write protected on
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* the fly. UFFDIO_COPY_MODE_WP is available only if the
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* write protected ioctl is implemented for the range
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* according to the uffdio_register.ioctls.
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*/
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#define UFFDIO_COPY_MODE_WP ((__u64)1<<1)
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__u64 mode;
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|
/*
|
|
* "copy" is written by the ioctl and must be at the end: the
|
|
* copy_from_user will not read the last 8 bytes.
|
|
*/
|
|
__s64 copy;
|
|
};
|
|
|
|
struct uffdio_zeropage {
|
|
struct uffdio_range range;
|
|
#define UFFDIO_ZEROPAGE_MODE_DONTWAKE ((__u64)1<<0)
|
|
__u64 mode;
|
|
|
|
/*
|
|
* "zeropage" is written by the ioctl and must be at the end:
|
|
* the copy_from_user will not read the last 8 bytes.
|
|
*/
|
|
__s64 zeropage;
|
|
};
|
|
|
|
struct uffdio_writeprotect {
|
|
struct uffdio_range range;
|
|
/*
|
|
* UFFDIO_WRITEPROTECT_MODE_WP: set the flag to write protect a range,
|
|
* unset the flag to undo protection of a range which was previously
|
|
* write protected.
|
|
*
|
|
* UFFDIO_WRITEPROTECT_MODE_DONTWAKE: set the flag to avoid waking up
|
|
* any wait thread after the operation succeeds.
|
|
*
|
|
* NOTE: Write protecting a region (WP=1) is unrelated to page faults,
|
|
* therefore DONTWAKE flag is meaningless with WP=1. Removing write
|
|
* protection (WP=0) in response to a page fault wakes the faulting
|
|
* task unless DONTWAKE is set.
|
|
*/
|
|
#define UFFDIO_WRITEPROTECT_MODE_WP ((__u64)1<<0)
|
|
#define UFFDIO_WRITEPROTECT_MODE_DONTWAKE ((__u64)1<<1)
|
|
__u64 mode;
|
|
};
|
|
|
|
struct uffdio_continue {
|
|
struct uffdio_range range;
|
|
#define UFFDIO_CONTINUE_MODE_DONTWAKE ((__u64)1<<0)
|
|
/*
|
|
* UFFDIO_CONTINUE_MODE_WP will map the page write protected on
|
|
* the fly. UFFDIO_CONTINUE_MODE_WP is available only if the
|
|
* write protected ioctl is implemented for the range
|
|
* according to the uffdio_register.ioctls.
|
|
*/
|
|
#define UFFDIO_CONTINUE_MODE_WP ((__u64)1<<1)
|
|
__u64 mode;
|
|
|
|
/*
|
|
* Fields below here are written by the ioctl and must be at the end:
|
|
* the copy_from_user will not read past here.
|
|
*/
|
|
__s64 mapped;
|
|
};
|
|
|
|
struct uffdio_poison {
|
|
struct uffdio_range range;
|
|
#define UFFDIO_POISON_MODE_DONTWAKE ((__u64)1<<0)
|
|
__u64 mode;
|
|
|
|
/*
|
|
* Fields below here are written by the ioctl and must be at the end:
|
|
* the copy_from_user will not read past here.
|
|
*/
|
|
__s64 updated;
|
|
};
|
|
|
|
/*
|
|
* Flags for the userfaultfd(2) system call itself.
|
|
*/
|
|
|
|
/*
|
|
* Create a userfaultfd that can handle page faults only in user mode.
|
|
*/
|
|
#define UFFD_USER_MODE_ONLY 1
|
|
|
|
#endif /* _LINUX_USERFAULTFD_H */
|