commit c88033efe9a391e72ba6b5df4b01d6e628f4e734 upstream.
Userfaultfd unregister includes a step to remove wr-protect bits from all
the relevant pgtable entries, but that only covered an explicit
UFFDIO_UNREGISTER ioctl, not a close() on the userfaultfd itself. Cover
that too. This fixes a WARN trace.
The only user visible side effect is the user can observe leftover
wr-protect bits even if the user close()ed on an userfaultfd when
releasing the last reference of it. However hopefully that should be
harmless, and nothing bad should happen even if so.
This change is now more important after the recent page-table-check
patch we merged in mm-unstable (446dd9ad37d0 ("mm/page_table_check:
support userfault wr-protect entries")), as we'll do sanity check on
uffd-wp bits without vma context. So it's better if we can 100%
guarantee no uffd-wp bit leftovers, to make sure each report will be
valid.
Link: https://lore.kernel.org/all/000000000000ca4df20616a0fe16@google.com/
Fixes: f369b07c8614 ("mm/uffd: reset write protection when unregister with wp-mode")
Analyzed-by: David Hildenbrand <david@redhat.com>
Link: https://lkml.kernel.org/r/20240422133311.2987675-1-peterx@redhat.com
Reported-by: syzbot+d8426b591c36b21c750e@syzkaller.appspotmail.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Pull kvm updates from Paolo Bonzini:
"Generic:
- Use memdup_array_user() to harden against overflow.
- Unconditionally advertise KVM_CAP_DEVICE_CTRL for all
architectures.
- Clean up Kconfigs that all KVM architectures were selecting
- New functionality around "guest_memfd", a new userspace API that
creates an anonymous file and returns a file descriptor that refers
to it. guest_memfd files are bound to their owning virtual machine,
cannot be mapped, read, or written by userspace, and cannot be
resized. guest_memfd files do however support PUNCH_HOLE, which can
be used to switch a memory area between guest_memfd and regular
anonymous memory.
- New ioctl KVM_SET_MEMORY_ATTRIBUTES allowing userspace to specify
per-page attributes for a given page of guest memory; right now the
only attribute is whether the guest expects to access memory via
guest_memfd or not, which in Confidential SVMs backed by SEV-SNP,
TDX or ARM64 pKVM is checked by firmware or hypervisor that
guarantees confidentiality (AMD PSP, Intel TDX module, or EL2 in
the case of pKVM).
x86:
- Support for "software-protected VMs" that can use the new
guest_memfd and page attributes infrastructure. This is mostly
useful for testing, since there is no pKVM-like infrastructure to
provide a meaningfully reduced TCB.
- Fix a relatively benign off-by-one error when splitting huge pages
during CLEAR_DIRTY_LOG.
- Fix a bug where KVM could incorrectly test-and-clear dirty bits in
non-leaf TDP MMU SPTEs if a racing thread replaces a huge SPTE with
a non-huge SPTE.
- Use more generic lockdep assertions in paths that don't actually
care about whether the caller is a reader or a writer.
- let Xen guests opt out of having PV clock reported as "based on a
stable TSC", because some of them don't expect the "TSC stable" bit
(added to the pvclock ABI by KVM, but never set by Xen) to be set.
- Revert a bogus, made-up nested SVM consistency check for
TLB_CONTROL.
- Advertise flush-by-ASID support for nSVM unconditionally, as KVM
always flushes on nested transitions, i.e. always satisfies flush
requests. This allows running bleeding edge versions of VMware
Workstation on top of KVM.
- Sanity check that the CPU supports flush-by-ASID when enabling SEV
support.
- On AMD machines with vNMI, always rely on hardware instead of
intercepting IRET in some cases to detect unmasking of NMIs
- Support for virtualizing Linear Address Masking (LAM)
- Fix a variety of vPMU bugs where KVM fail to stop/reset counters
and other state prior to refreshing the vPMU model.
- Fix a double-overflow PMU bug by tracking emulated counter events
using a dedicated field instead of snapshotting the "previous"
counter. If the hardware PMC count triggers overflow that is
recognized in the same VM-Exit that KVM manually bumps an event
count, KVM would pend PMIs for both the hardware-triggered overflow
and for KVM-triggered overflow.
- Turn off KVM_WERROR by default for all configs so that it's not
inadvertantly enabled by non-KVM developers, which can be
problematic for subsystems that require no regressions for W=1
builds.
- Advertise all of the host-supported CPUID bits that enumerate
IA32_SPEC_CTRL "features".
- Don't force a masterclock update when a vCPU synchronizes to the
current TSC generation, as updating the masterclock can cause
kvmclock's time to "jump" unexpectedly, e.g. when userspace
hotplugs a pre-created vCPU.
- Use RIP-relative address to read kvm_rebooting in the VM-Enter
fault paths, partly as a super minor optimization, but mostly to
make KVM play nice with position independent executable builds.
- Guard KVM-on-HyperV's range-based TLB flush hooks with an #ifdef on
CONFIG_HYPERV as a minor optimization, and to self-document the
code.
- Add CONFIG_KVM_HYPERV to allow disabling KVM support for HyperV
"emulation" at build time.
ARM64:
- LPA2 support, adding 52bit IPA/PA capability for 4kB and 16kB base
granule sizes. Branch shared with the arm64 tree.
- Large Fine-Grained Trap rework, bringing some sanity to the
feature, although there is more to come. This comes with a prefix
branch shared with the arm64 tree.
- Some additional Nested Virtualization groundwork, mostly
introducing the NV2 VNCR support and retargetting the NV support to
that version of the architecture.
- A small set of vgic fixes and associated cleanups.
Loongarch:
- Optimization for memslot hugepage checking
- Cleanup and fix some HW/SW timer issues
- Add LSX/LASX (128bit/256bit SIMD) support
RISC-V:
- KVM_GET_REG_LIST improvement for vector registers
- Generate ISA extension reg_list using macros in get-reg-list
selftest
- Support for reporting steal time along with selftest
s390:
- Bugfixes
Selftests:
- Fix an annoying goof where the NX hugepage test prints out garbage
instead of the magic token needed to run the test.
- Fix build errors when a header is delete/moved due to a missing
flag in the Makefile.
- Detect if KVM bugged/killed a selftest's VM and print out a helpful
message instead of complaining that a random ioctl() failed.
- Annotate the guest printf/assert helpers with __printf(), and fix
the various bugs that were lurking due to lack of said annotation"
* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (185 commits)
x86/kvm: Do not try to disable kvmclock if it was not enabled
KVM: x86: add missing "depends on KVM"
KVM: fix direction of dependency on MMU notifiers
KVM: introduce CONFIG_KVM_COMMON
KVM: arm64: Add missing memory barriers when switching to pKVM's hyp pgd
KVM: arm64: vgic-its: Avoid potential UAF in LPI translation cache
RISC-V: KVM: selftests: Add get-reg-list test for STA registers
RISC-V: KVM: selftests: Add steal_time test support
RISC-V: KVM: selftests: Add guest_sbi_probe_extension
RISC-V: KVM: selftests: Move sbi_ecall to processor.c
RISC-V: KVM: Implement SBI STA extension
RISC-V: KVM: Add support for SBI STA registers
RISC-V: KVM: Add support for SBI extension registers
RISC-V: KVM: Add SBI STA info to vcpu_arch
RISC-V: KVM: Add steal-update vcpu request
RISC-V: KVM: Add SBI STA extension skeleton
RISC-V: paravirt: Implement steal-time support
RISC-V: Add SBI STA extension definitions
RISC-V: paravirt: Add skeleton for pv-time support
RISC-V: KVM: Fix indentation in kvm_riscv_vcpu_set_reg_csr()
...
Pull sysctl updates from Luis Chamberlain:
"To help make the move of sysctls out of kernel/sysctl.c not incur a
size penalty sysctl has been changed to allow us to not require the
sentinel, the final empty element on the sysctl array. Joel Granados
has been doing all this work.
In the v6.6 kernel we got the major infrastructure changes required to
support this. For v6.7 we had all arch/ and drivers/ modified to
remove the sentinel. For v6.8-rc1 we get a few more updates for fs/
directory only.
The kernel/ directory is left but we'll save that for v6.9-rc1 as
those patches are still being reviewed. After that we then can expect
also the removal of the no longer needed check for procname == NULL.
Let us recap the purpose of this work:
- this helps reduce the overall build time size of the kernel and run
time memory consumed by the kernel by about ~64 bytes per array
- the extra 64-byte penalty is no longer inncurred now when we move
sysctls out from kernel/sysctl.c to their own files
Thomas Weißschuh also sent a few cleanups, for v6.9-rc1 we expect to
see further work by Thomas Weißschuh with the constificatin of the
struct ctl_table.
Due to Joel Granados's work, and to help bring in new blood, I have
suggested for him to become a maintainer and he's accepted. So for
v6.9-rc1 I look forward to seeing him sent you a pull request for
further sysctl changes. This also removes Iurii Zaikin as a maintainer
as he has moved on to other projects and has had no time to help at
all"
* tag 'sysctl-6.8-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux:
sysctl: remove struct ctl_path
sysctl: delete unused define SYSCTL_PERM_EMPTY_DIR
coda: Remove the now superfluous sentinel elements from ctl_table array
sysctl: Remove the now superfluous sentinel elements from ctl_table array
fs: Remove the now superfluous sentinel elements from ctl_table array
cachefiles: Remove the now superfluous sentinel element from ctl_table array
sysclt: Clarify the results of selftest run
sysctl: Add a selftest for handling empty dirs
sysctl: Fix out of bounds access for empty sysctl registers
MAINTAINERS: Add Joel Granados as co-maintainer for proc sysctl
MAINTAINERS: remove Iurii Zaikin from proc sysctl
Implement the uABI of UFFDIO_MOVE ioctl.
UFFDIO_COPY performs ~20% better than UFFDIO_MOVE when the application
needs pages to be allocated [1]. However, with UFFDIO_MOVE, if pages are
available (in userspace) for recycling, as is usually the case in heap
compaction algorithms, then we can avoid the page allocation and memcpy
(done by UFFDIO_COPY). Also, since the pages are recycled in the
userspace, we avoid the need to release (via madvise) the pages back to
the kernel [2].
We see over 40% reduction (on a Google pixel 6 device) in the compacting
thread's completion time by using UFFDIO_MOVE vs. UFFDIO_COPY. This was
measured using a benchmark that emulates a heap compaction implementation
using userfaultfd (to allow concurrent accesses by application threads).
More details of the usecase are explained in [2]. Furthermore,
UFFDIO_MOVE enables moving swapped-out pages without touching them within
the same vma. Today, it can only be done by mremap, however it forces
splitting the vma.
[1] https://lore.kernel.org/all/1425575884-2574-1-git-send-email-aarcange@redhat.com/
[2] https://lore.kernel.org/linux-mm/CA+EESO4uO84SSnBhArH4HvLNhaUQ5nZKNKXqxRCyjniNVjp0Aw@mail.gmail.com/
Update for the ioctl_userfaultfd(2) manpage:
UFFDIO_MOVE
(Since Linux xxx) Move a continuous memory chunk into the
userfault registered range and optionally wake up the blocked
thread. The source and destination addresses and the number of
bytes to move are specified by the src, dst, and len fields of
the uffdio_move structure pointed to by argp:
struct uffdio_move {
__u64 dst; /* Destination of move */
__u64 src; /* Source of move */
__u64 len; /* Number of bytes to move */
__u64 mode; /* Flags controlling behavior of move */
__s64 move; /* Number of bytes moved, or negated error */
};
The following value may be bitwise ORed in mode to change the
behavior of the UFFDIO_MOVE operation:
UFFDIO_MOVE_MODE_DONTWAKE
Do not wake up the thread that waits for page-fault
resolution
UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES
Allow holes in the source virtual range that is being moved.
When not specified, the holes will result in ENOENT error.
When specified, the holes will be accounted as successfully
moved memory. This is mostly useful to move hugepage aligned
virtual regions without knowing if there are transparent
hugepages in the regions or not, but preventing the risk of
having to split the hugepage during the operation.
The move field is used by the kernel to return the number of
bytes that was actually moved, or an error (a negated errno-
style value). If the value returned in move doesn't match the
value that was specified in len, the operation fails with the
error EAGAIN. The move field is output-only; it is not read by
the UFFDIO_MOVE operation.
The operation may fail for various reasons. Usually, remapping of
pages that are not exclusive to the given process fail; once KSM
might deduplicate pages or fork() COW-shares pages during fork()
with child processes, they are no longer exclusive. Further, the
kernel might only perform lightweight checks for detecting whether
the pages are exclusive, and return -EBUSY in case that check fails.
To make the operation more likely to succeed, KSM should be
disabled, fork() should be avoided or MADV_DONTFORK should be
configured for the source VMA before fork().
This ioctl(2) operation returns 0 on success. In this case, the
entire area was moved. On error, -1 is returned and errno is
set to indicate the error. Possible errors include:
EAGAIN The number of bytes moved (i.e., the value returned in
the move field) does not equal the value that was
specified in the len field.
EINVAL Either dst or len was not a multiple of the system page
size, or the range specified by src and len or dst and len
was invalid.
EINVAL An invalid bit was specified in the mode field.
ENOENT
The source virtual memory range has unmapped holes and
UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES is not set.
EEXIST
The destination virtual memory range is fully or partially
mapped.
EBUSY
The pages in the source virtual memory range are either
pinned or not exclusive to the process. The kernel might
only perform lightweight checks for detecting whether the
pages are exclusive. To make the operation more likely to
succeed, KSM should be disabled, fork() should be avoided
or MADV_DONTFORK should be configured for the source virtual
memory area before fork().
ENOMEM Allocating memory needed for the operation failed.
ESRCH
The target process has exited at the time of a UFFDIO_MOVE
operation.
Link: https://lkml.kernel.org/r/20231206103702.3873743-3-surenb@google.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Nicolas Geoffray <ngeoffray@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: ZhangPeng <zhangpeng362@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit comes at the tail end of a greater effort to remove the empty elements at the end of the ctl_table arrays (sentinels) which will reduce the overall build time size of the kernel and run time memory bloat by ~64 bytes per sentinel (further information Link : https://lore.kernel.org/all/ZO5Yx5JFogGi%2FcBo@bombadil.infradead.org/) Remove sentinel elements ctl_table struct. Special attention was placed in making sure that an empty directory for fs/verity was created when CONFIG_FS_VERITY_BUILTIN_SIGNATURES is not defined. In this case we use the register sysctl call that expects a size. Signed-off-by: Joel Granados <j.granados@samsung.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: "Darrick J. Wong" <djwong@kernel.org> Acked-by: Christian Brauner <brauner@kernel.org> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Introduce several new KVM uAPIs to ultimately create a guest-first memory
subsystem within KVM, a.k.a. guest_memfd. Guest-first memory allows KVM
to provide features, enhancements, and optimizations that are kludgly
or outright impossible to implement in a generic memory subsystem.
The core KVM ioctl() for guest_memfd is KVM_CREATE_GUEST_MEMFD, which
similar to the generic memfd_create(), creates an anonymous file and
returns a file descriptor that refers to it. Again like "regular"
memfd files, guest_memfd files live in RAM, have volatile storage,
and are automatically released when the last reference is dropped.
The key differences between memfd files (and every other memory subystem)
is that guest_memfd files are bound to their owning virtual machine,
cannot be mapped, read, or written by userspace, and cannot be resized.
guest_memfd files do however support PUNCH_HOLE, which can be used to
convert a guest memory area between the shared and guest-private states.
A second KVM ioctl(), KVM_SET_MEMORY_ATTRIBUTES, allows userspace to
specify attributes for a given page of guest memory. In the long term,
it will likely be extended to allow userspace to specify per-gfn RWX
protections, including allowing memory to be writable in the guest
without it also being writable in host userspace.
The immediate and driving use case for guest_memfd are Confidential
(CoCo) VMs, specifically AMD's SEV-SNP, Intel's TDX, and KVM's own pKVM.
For such use cases, being able to map memory into KVM guests without
requiring said memory to be mapped into the host is a hard requirement.
While SEV+ and TDX prevent untrusted software from reading guest private
data by encrypting guest memory, pKVM provides confidentiality and
integrity *without* relying on memory encryption. In addition, with
SEV-SNP and especially TDX, accessing guest private memory can be fatal
to the host, i.e. KVM must be prevent host userspace from accessing
guest memory irrespective of hardware behavior.
Long term, guest_memfd may be useful for use cases beyond CoCo VMs,
for example hardening userspace against unintentional accesses to guest
memory. As mentioned earlier, KVM's ABI uses userspace VMA protections to
define the allow guest protection (with an exception granted to mapping
guest memory executable), and similarly KVM currently requires the guest
mapping size to be a strict subset of the host userspace mapping size.
Decoupling the mappings sizes would allow userspace to precisely map
only what is needed and with the required permissions, without impacting
guest performance.
A guest-first memory subsystem also provides clearer line of sight to
things like a dedicated memory pool (for slice-of-hardware VMs) and
elimination of "struct page" (for offload setups where userspace _never_
needs to DMA from or into guest memory).
guest_memfd is the result of 3+ years of development and exploration;
taking on memory management responsibilities in KVM was not the first,
second, or even third choice for supporting CoCo VMs. But after many
failed attempts to avoid KVM-specific backing memory, and looking at
where things ended up, it is quite clear that of all approaches tried,
guest_memfd is the simplest, most robust, and most extensible, and the
right thing to do for KVM and the kernel at-large.
The "development cycle" for this version is going to be very short;
ideally, next week I will merge it as is in kvm/next, taking this through
the KVM tree for 6.8 immediately after the end of the merge window.
The series is still based on 6.6 (plus KVM changes for 6.7) so it
will require a small fixup for changes to get_file_rcu() introduced in
6.7 by commit 0ede61d8589c ("file: convert to SLAB_TYPESAFE_BY_RCU").
The fixup will be done as part of the merge commit, and most of the text
above will become the commit message for the merge.
Pending post-merge work includes:
- hugepage support
- looking into using the restrictedmem framework for guest memory
- introducing a testing mechanism to poison memory, possibly using
the same memory attributes introduced here
- SNP and TDX support
There are two non-KVM patches buried in the middle of this series:
fs: Rename anon_inode_getfile_secure() and anon_inode_getfd_secure()
mm: Add AS_UNMOVABLE to mark mapping as completely unmovable
The first is small and mostly suggested-by Christian Brauner; the second
a bit less so but it was written by an mm person (Vlastimil Babka).
The call to the inode_init_security_anon() LSM hook is not the sole
reason to use anon_inode_getfile_secure() or anon_inode_getfd_secure().
For example, the functions also allow one to create a file with non-zero
size, without needing a full-blown filesystem. In this case, you don't
need a "secure" version, just unique inodes; the current name of the
functions is confusing and does not explain well the difference with
the more "standard" anon_inode_getfile() and anon_inode_getfd().
Of course, there is another side of the coin; neither io_uring nor
userfaultfd strictly speaking need distinct inodes, and it is not
that clear anymore that anon_inode_create_get{file,fd}() allow the LSM
to intercept and block the inode's creation. If one was so inclined,
anon_inode_getfile_secure() and anon_inode_getfd_secure() could be kept,
using the shared inode or a new one depending on CONFIG_SECURITY.
However, this is probably overkill, and potentially a cause of bugs in
different configurations. Therefore, just add a comment to io_uring
and userfaultfd explaining the choice of the function.
While at it, remove the export for what is now anon_inode_create_getfd().
There is no in-tree module that uses it, and the old name is gone anyway.
If anybody actually needs the symbol, they can ask or they can just use
anon_inode_create_getfile(), which will be exported very soon for use
in KVM.
Suggested-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Pull non-MM updates from Andrew Morton:
"As usual, lots of singleton and doubleton patches all over the tree
and there's little I can say which isn't in the individual changelogs.
The lengthier patch series are
- 'kdump: use generic functions to simplify crashkernel reservation
in arch', from Baoquan He. This is mainly cleanups and
consolidation of the 'crashkernel=' kernel parameter handling
- After much discussion, David Laight's 'minmax: Relax type checks in
min() and max()' is here. Hopefully reduces some typecasting and
the use of min_t() and max_t()
- A group of patches from Oleg Nesterov which clean up and slightly
fix our handling of reads from /proc/PID/task/... and which remove
task_struct.thread_group"
* tag 'mm-nonmm-stable-2023-11-02-14-08' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (64 commits)
scripts/gdb/vmalloc: disable on no-MMU
scripts/gdb: fix usage of MOD_TEXT not defined when CONFIG_MODULES=n
.mailmap: add address mapping for Tomeu Vizoso
mailmap: update email address for Claudiu Beznea
tools/testing/selftests/mm/run_vmtests.sh: lower the ptrace permissions
.mailmap: map Benjamin Poirier's address
scripts/gdb: add lx_current support for riscv
ocfs2: fix a spelling typo in comment
proc: test ProtectionKey in proc-empty-vm test
proc: fix proc-empty-vm test with vsyscall
fs/proc/base.c: remove unneeded semicolon
do_io_accounting: use sig->stats_lock
do_io_accounting: use __for_each_thread()
ocfs2: replace BUG_ON() at ocfs2_num_free_extents() with ocfs2_error()
ocfs2: fix a typo in a comment
scripts/show_delta: add __main__ judgement before main code
treewide: mark stuff as __ro_after_init
fs: ocfs2: check status values
proc: test /proc/${pid}/statm
compiler.h: move __is_constexpr() to compiler.h
...
__read_mostly predates __ro_after_init. Many variables which are marked __read_mostly should have been __ro_after_init from day 1. Also, mark some stuff as "const" and "__init" while I'm at it. [akpm@linux-foundation.org: revert sysctl_nr_open_min, sysctl_nr_open_max changes due to arm warning] [akpm@linux-foundation.org: coding-style cleanups] Link: https://lkml.kernel.org/r/4f6bb9c0-abba-4ee4-a7aa-89265e886817@p183 Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
mprotect() and other functions which change VMA parameters over a range each employ a pattern of:- 1. Attempt to merge the range with adjacent VMAs. 2. If this fails, and the range spans a subset of the VMA, split it accordingly. This is open-coded and duplicated in each case. Also in each case most of the parameters passed to vma_merge() remain the same. Create a new function, vma_modify(), which abstracts this operation, accepting only those parameters which can be changed. To avoid the mess of invoking each function call with unnecessary parameters, create inline wrapper functions for each of the modify operations, parameterised only by what is required to perform the action. We can also significantly simplify the logic - by returning the VMA if we split (or merged VMA if we do not) we no longer need specific handling for merge/split cases in any of the call sites. Note that the userfaultfd_release() case works even though it does not split VMAs - since start is set to vma->vm_start and end is set to vma->vm_end, the split logic does not trigger. In addition, since we calculate pgoff to be equal to vma->vm_pgoff + (start - vma->vm_start) >> PAGE_SHIFT, and start - vma->vm_start will be 0 in this instance, this invocation will remain unchanged. We eliminate a VM_WARN_ON() in mprotect_fixup() as this simply asserts that vma_merge() correctly ensures that flags remain the same, something that is already checked in is_mergeable_vma() and elsewhere, and in any case is not specific to mprotect(). Link: https://lkml.kernel.org/r/0dfa9368f37199a423674bf0ee312e8ea0619044.1697043508.git.lstoakes@gmail.com Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Christian Brauner <brauner@kernel.org> Cc: Liam R. Howlett <Liam.Howlett@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>