Commit c010d47f10 ("mm: thp: split huge page to any lower order pages")
introduced an early check on the folio's order via mapping->flags before
proceeding with the split work.
This check introduced a bug: for shmem folios in the swap cache and
truncated folios, the mapping pointer can be NULL. Accessing
mapping->flags in this state leads directly to a NULL pointer dereference.
This commit fixes the issue by moving the check for mapping != NULL before
any attempt to access mapping->flags.
Link: https://lkml.kernel.org/r/20251119235302.24773-1-richard.weiyang@gmail.com
Fixes: c010d47f10 ("mm: thp: split huge page to any lower order pages")
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
After commit 4f78252da8, nr_swap_pages is decremented in
swap_range_alloc(). Since cluster_alloc_swap_entry() calls
swap_range_alloc() internally, the decrement in get_swap_page_of_type()
causes double-decrementing.
As a representative userspace-visible runtime example of the impact,
/proc/meminfo reports increasingly inaccurate SwapFree values. The
discrepancy grows with each swap allocation, and during hibernation
when large amounts of memory are written to swap, the reported value
can deviate significantly from actual available swap space, misleading
users and monitoring tools.
Remove the duplicate decrement.
Link: https://lkml.kernel.org/r/20251102082456.79807-1-youngjun.park@lge.com
Fixes: 4f78252da8 ("mm: swap: move nr_swap_pages counter decrement from folio_alloc_swap() to swap_range_alloc()")
Signed-off-by: Youngjun Park <youngjun.park@lge.com>
Acked-by: Chris Li <chrisl@kernel.org>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Kairui Song <kasong@tencent.com>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: <stable@vger.kernel.org> [6.17+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Assert that we correctly merge VMAs containing VM_SOFTDIRTY flags now that
we correctly handle these as sticky.
In order to do so, we have to account for the fact the pagemap interface
checks soft dirty PTEs and additionally that newly merged VMAs are marked
VM_SOFTDIRTY.
We do this by using use unfaulted anon VMAs, establishing one and clearing
references on that one, before establishing another and merging the two
before checking that soft-dirty is propagated as expected.
We check that this functions correctly with mremap() and mprotect() as
sample cases, because VMA merge of adjacent newly mapped VMAs will
automatically be made soft-dirty due to existing logic which does so.
We are therefore exercising other means of merging VMAs.
Link: https://lkml.kernel.org/r/d5a0f735783fb4f30a604f570ede02ccc5e29be9.1763399675.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Andrey Vagin <avagin@gmail.com>
Cc: David Hildenbrand (Red Hat) <david@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "make VM_SOFTDIRTY a sticky VMA flag", v2.
Currently we set VM_SOFTDIRTY when a new mapping is set up (whether by
establishing a new VMA, or via merge) as implemented in __mmap_complete()
and do_brk_flags().
However, when performing a merge of existing mappings such as when
performing mprotect(), we may lose the VM_SOFTDIRTY flag.
Now we have the concept of making VMA flags 'sticky', that is that they
both don't prevent merge and, importantly, are propagated to merged VMAs,
this seems a sensible alternative to the existing special-casing of
VM_SOFTDIRTY.
We additionally add a self-test that demonstrates that this logic behaves
as expected.
This patch (of 2):
Currently we set VM_SOFTDIRTY when a new mapping is set up (whether by
establishing a new VMA, or via merge) as implemented in __mmap_complete()
and do_brk_flags().
However, when performing a merge of existing mappings such as when
performing mprotect(), we may lose the VM_SOFTDIRTY flag.
This is because currently we simply ignore VM_SOFTDIRTY for the purposes
of merge, so one VMA may possess the flag and another not, and whichever
happens to be the target VMA will be the one upon which the merge is
performed which may or may not have VM_SOFTDIRTY set.
Now we have the concept of 'sticky' VMA flags, let's make VM_SOFTDIRTY one
which solves this issue.
Additionally update VMA userland tests to propagate changes.
[akpm@linux-foundation.org: update comments, per Lorenzo]
Link: https://lkml.kernel.org/r/0019e0b8-ee1e-4359-b5ee-94225cbe5588@lucifer.local
Link: https://lkml.kernel.org/r/cover.1763399675.git.lorenzo.stoakes@oracle.com
Link: https://lkml.kernel.org/r/955478b5170715c895d1ef3b7f68e0cd77f76868.1763399675.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Acked-by: Andrey Vagin <avagin@gmail.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm/damon: misc cleanups".
Yet another batch of misc cleanups and refactoring for DAMON code, tests,
and documents.
First two patches (1and 2) rename DAMOS core filters related code for
readability.
Three following patches (3-5) refactor page table walk callback functions
in DAMON, as suggested by Hugh and David, and I promised.
Next two patches (6 and 7) refactor DAMON core layer kunit test and sysfs
interface selftest to be simple and deduplicated.
Final two patches (8 and 9) fix up sphinx and grammatical errors on
documents.
This patch (of 9):
DAMOS filters handled by the core layer are called core filters, while
those handled by the ops layer are called ops filters. They share the
same type but are managed in different places since core filters are
evaluated before the ops filters. They also have different helper
functions that depend on their managed places.
The helper functions for ops filters have '_ops_' keyword on their name,
so it is easy to know they are for ops filters. Meanwhile, the helper
functions for core filters are not having the 'core' keyword on their
name. This makes it easy to be mistakenly used for ops filters. Actually
there was such a bug.
To avoid future mistakes from similar confusions, rename DAMOS core
filters helper functions to have a keyword 'core' on their names.
Link: https://lkml.kernel.org/r/20251112154114.66053-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20251112154114.66053-2-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Bill Wendling <morbo@google.com>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Gow <davidgow@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Justin Stitt <justinstitt@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: David Hildenbrand <david@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm/damon/tests: add more tests for online parameters commit".
A DAMON feature called parameters "commit" allows DAMON API callers and
ABI users to update nearly every DAMON parameter while DAMON is running.
This is being used for flexible DAMON use cases such as taking a snapshot
of the monitoring results with minimum overhead, or adjusting access-aware
system operations (DAMOS) for user-space driven auto-tuning or
investigations.
Compared to the usefulness of the feature and size of the implementation,
the test coverage is pretty small. Only the filter commit part has a
single test case, namely damos_test_commit_filter(). Actually, we found
and fixed a few bugs of the feature in the past. The single existing test
was also added to avoid reintroduction of a found bug.
Add more unit tests for the feature.
First four patches (1-4) refactor and extend the existing test for DAMOS
filter commit for multiple test cases.
Next three patches (5-7) add tests for DAMOS quota commit.
Next two patches (8 and 9) refactor damos_commit_dests() for ease of code
reading and test writing, and implement a new unit test of the function
that is being refactored in a test-friendly way.
Final two patches (10 and 11) further add new unit tests for
damos_commit() and damon_commit_target_regions().
This patch (of 11):
damos_test_commit_filter() is dynamically allocating test-purpose DAMOS
filters. Allocation failure checks are making the code longer,
complicated, and difficult to extend for more test cases. Refactor the
code to remove the dynamic allocation.
Link: https://lkml.kernel.org/r/20251111184415.141757-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20251111184415.141757-2-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Gow <davidgow@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "vma_start_write_killable"", v2.
When we added the VMA lock, we made a major oversight in not adding a
killable variant. That can run us into trouble where a thread takes the
VMA lock for read (eg handling a page fault) and then goes out to lunch
for an hour (eg doing reclaim). Another thread tries to modify the VMA,
taking the mmap_lock for write, then attempts to lock the VMA for write.
That blocks on the first thread, and ensures that every other page fault
now tries to take the mmap_lock for read. Because everything's in an
uninterruptible sleep, we can't kill the task, which makes me angry.
This patchset just adds vma_start_write_killable() and converts one caller
to use it. Most users are somewhat tricky to convert, so expect follow-up
individual patches per call-site which need careful analysis to make sure
we've done proper cleanup.
This patch (of 2):
The vma can be held read-locked for a substantial period of time, eg if
memory allocation needs to go into reclaim. It's useful to be able to
send fatal signals to threads which are waiting for the write lock.
Link: https://lkml.kernel.org/r/20251110203204.1454057-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20251110203204.1454057-2-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Chris Li <chriscli@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
We only need to keep the page table stable so we can perform this
operation under the VMA lock. PTE installation is stabilised via the PTE
lock.
One caveat is that, if we prepare vma->anon_vma we must hold the mmap read
lock. We can account for this by adapting the VMA locking logic to
explicitly check for this case and prevent a VMA lock from being acquired
should it be the case.
This check is safe, as while we might be raced on anon_vma installation,
this would simply make the check conservative, there's no way for us to
see an anon_vma and then for it to be cleared, as doing so requires the
mmap/VMA write lock.
We abstract the VMA lock validity logic to is_vma_lock_sufficient() for
this purpose, and add prepares_anon_vma() to abstract the anon_vma logic.
In order to do this we need to have a way of installing page tables
explicitly for an identified VMA, so we export walk_page_range_vma() in an
unsafe variant - walk_page_range_vma_unsafe() and use this should the VMA
read lock be taken.
We additionally update the comments in madvise_guard_install() to more
accurately reflect the cases in which the logic may be reattempted,
specifically THP huge pages being present.
Link: https://lkml.kernel.org/r/cca1edbd99cd1386ad20556d08ebdb356c45ef91.1762795245.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: SeongJae Park <sj@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm: perform guard region install/remove under VMA lock", v2.
There is no reason why can't perform guard region operations under the VMA
lock, as long we take proper precautions to ensure that we do so in a safe
manner.
This is fine, as VMA lock acquisition is always best-effort, so if we are
unable to do so, we can simply fall back to using the mmap read lock.
Doing so will reduce mmap lock contention for callers performing guard
region operations and help establish a precedent of trying to use the VMA
lock where possible.
As part of this change we perform a trivial rename of page walk functions
which bypass safety checks (i.e. whether or not mm_walk_ops->install_pte
is specified) in order that we can keep naming consistent with the mm
walk.
This is because we need to expose a VMA-specific walk that still allows us
to install PTE entries.
This patch (of 2):
Make it clear we're referencing an unsafe variant of this function
explicitly.
This is laying the foundation for exposing more such functions and
maintaining a consistent naming scheme.
As a part of this change, rename check_ops_valid() to check_ops_safe() for
consistency.
Link: https://lkml.kernel.org/r/cover.1762795245.git.lorenzo.stoakes@oracle.com
Link: https://lkml.kernel.org/r/c684d91464a438d6e31172c9450416a373f10649.1762795245.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: SeongJae Park <sj@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Now we have established the VM_MAYBE_GUARD flag and added the capacity to
set it atomically, do so upon MADV_GUARD_INSTALL.
The places where this flag is used currently and matter are:
* VMA merge - performed under mmap/VMA write lock, therefore excluding
racing writes.
* /proc/$pid/smaps - can race the write, however this isn't meaningful
as the flag write is performed at the point of the guard region being
established, and thus an smaps reader can't reasonably expect to avoid
races. Due to atomicity, a reader will observe either the flag being
set or not. Therefore consistency will be maintained.
In all other cases the flag being set is irrelevant and atomicity
guarantees other flags will be read correctly.
Note that non-atomic updates of unrelated flags do not cause an issue with
this flag being set atomically, as writes of other flags are performed
under mmap/VMA write lock, and these atomic writes are performed under
mmap/VMA read lock, which excludes the write, avoiding RMW races.
Note that we do not encounter issues with KCSAN by adjusting this flag
atomically, as we are only updating a single bit in the flag bitmap and
therefore we do not need to annotate these changes.
We intentionally set this flag in advance of actually updating the page
tables, to ensure that any racing atomic read of this flag will only
return false prior to page tables being updated, to allow for
serialisation via page table locks.
Note that we set vma->anon_vma for anonymous mappings. This is because
the expectation for anonymous mappings is that an anon_vma is established
should they possess any page table mappings. This is also consistent with
what we were doing prior to this patch (unconditionally setting anon_vma
on guard region installation).
We also need to update retract_page_tables() to ensure that madvise(...,
MADV_COLLAPSE) doesn't incorrectly collapse file-backed ranges contain
guard regions.
This was previously guarded by anon_vma being set to catch MAP_PRIVATE
cases, but the introduction of VM_MAYBE_GUARD necessitates that we check
this flag instead.
We utilise vma_flag_test_atomic() to do so - we first perform an
optimistic check, then after the PTE page table lock is held, we can check
again safely, as upon guard marker install the flag is set atomically
prior to the page table lock being taken to actually apply it.
So if the initial check fails either:
* Page table retraction acquires page table lock prior to VM_MAYBE_GUARD
being set - guard marker installation will be blocked until page table
retraction is complete.
OR:
* Guard marker installation acquires page table lock after setting
VM_MAYBE_GUARD, which raced and didn't pick this up in the initial
optimistic check, blocking page table retraction until the guard regions
are installed - the second VM_MAYBE_GUARD check will prevent page table
retraction.
Either way we're safe.
We refactor the retraction checks into a single
file_backed_vma_is_retractable(), there doesn't seem to be any reason that
the checks were separated as before.
Note that VM_MAYBE_GUARD being set atomically remains correct as
vma_needs_copy() is invoked with the mmap and VMA write locks held,
excluding any race with madvise_guard_install().
Link: https://lkml.kernel.org/r/e9e9ce95b6ac17497de7f60fc110c7dd9e489e8d.1763460113.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand (Red Hat) <david@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
It is useful to be able to designate that certain flags are 'sticky', that
is, if two VMAs are merged one with a flag of this nature and one without,
the merged VMA sets this flag.
As a result we ignore these flags for the purposes of determining VMA flag
differences between VMAs being considered for merge.
This patch therefore updates the VMA merge logic to perform this action,
with flags possessing this property being described in the VM_STICKY
bitmap.
Those flags which ought to be ignored for the purposes of VMA merge are
described in the VM_IGNORE_MERGE bitmap, which the VMA merge logic is also
updated to use.
As part of this change we place VM_SOFTDIRTY in VM_IGNORE_MERGE as it
already had this behaviour, alongside VM_STICKY as sticky flags by
implication must not disallow merge.
Ultimately it seems that we should make VM_SOFTDIRTY a sticky flag in its
own right, but this change is out of scope for this series.
The only sticky flag designated as such is VM_MAYBE_GUARD, so as a result
of this change, once the VMA flag is set upon guard region installation,
VMAs with guard ranges will now not have their merge behaviour impacted as
a result and can be freely merged with other VMAs without VM_MAYBE_GUARD
set.
Also update the comments for vma_modify_flags() to directly reference
sticky flags now we have established the concept.
We also update the VMA userland tests to account for the changes.
Link: https://lkml.kernel.org/r/22ad5269f7669d62afb42ce0c79bad70b994c58d.1763460113.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand (Red Hat) <david@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "introduce VM_MAYBE_GUARD and make it sticky", v4.
Currently, guard regions are not visible to users except through
/proc/$pid/pagemap, with no explicit visibility at the VMA level.
This makes the feature less useful, as it isn't entirely apparent which
VMAs may have these entries present, especially when performing actions
which walk through memory regions such as those performed by CRIU.
This series addresses this issue by introducing the VM_MAYBE_GUARD flag
which fulfils this role, updating the smaps logic to display an entry for
these.
The semantics of this flag are that a guard region MAY be present if set
(we cannot be sure, as we can't efficiently track whether an
MADV_GUARD_REMOVE finally removes all the guard regions in a VMA) - but if
not set the VMA definitely does NOT have any guard regions present.
It's problematic to establish this flag without further action, because
that means that VMAs with guard regions in them become non-mergeable with
adjacent VMAs for no especially good reason.
To work around this, this series also introduces the concept of 'sticky'
VMA flags - that is flags which:
a. if set in one VMA and not in another still permit those VMAs to be
merged (if otherwise compatible).
b. When they are merged, the resultant VMA must have the flag set.
The VMA logic is updated to propagate these flags correctly.
Additionally, VM_MAYBE_GUARD being an explicit VMA flag allows us to solve
an issue with file-backed guard regions - previously these established an
anon_vma object for file-backed mappings solely to have vma_needs_copy()
correctly propagate guard region mappings to child processes.
We introduce a new flag alias VM_COPY_ON_FORK (which currently only
specifies VM_MAYBE_GUARD) and update vma_needs_copy() to check explicitly
for this flag and to copy page tables if it is present, which resolves
this issue.
Additionally, we add the ability for allow-listed VMA flags to be
atomically writable with only mmap/VMA read locks held.
The only flag we allow so far is VM_MAYBE_GUARD, which we carefully ensure
does not cause any races by being allowed to do so.
This allows us to maintain guard region installation as a read-locked
operation and not endure the overhead of obtaining a write lock here.
Finally we introduce extensive VMA userland tests to assert that the
sticky VMA logic behaves correctly as well as guard region self tests to
assert that smaps visibility is correctly implemented.
This patch (of 9):
Currently, if a user needs to determine if guard regions are present in a
range, they have to scan all VMAs (or have knowledge of which ones might
have guard regions).
Since commit 8e2f2aeb8b ("fs/proc/task_mmu: add guard region bit to
pagemap") and the related commit a516403787 ("fs/proc: extend the
PAGEMAP_SCAN ioctl to report guard regions"), users can use either
/proc/$pid/pagemap or the PAGEMAP_SCAN functionality to perform this
operation at a virtual address level.
This is not ideal, and it gives no visibility at a /proc/$pid/smaps level
that guard regions exist in ranges.
This patch remedies the situation by establishing a new VMA flag,
VM_MAYBE_GUARD, to indicate that a VMA may contain guard regions (it is
uncertain because we cannot reasonably determine whether a
MADV_GUARD_REMOVE call has removed all of the guard regions in a VMA, and
additionally VMAs may change across merge/split).
We utilise 0x800 for this flag which makes it available to 32-bit
architectures also, a flag that was previously used by VM_DENYWRITE, which
was removed in commit 8d0920bde5 ("mm: remove VM_DENYWRITE") and hasn't
bee reused yet.
We also update the smaps logic and documentation to identify these VMAs.
Another major use of this functionality is that we can use it to identify
that we ought to copy page tables on fork.
We do not actually implement usage of this flag in mm/madvise.c yet as we
need to allow some VMA flags to be applied atomically under mmap/VMA read
lock in order to avoid the need to acquire a write lock for this purpose.
Link: https://lkml.kernel.org/r/cover.1763460113.git.lorenzo.stoakes@oracle.com
Link: https://lkml.kernel.org/r/cf8ef821eba29b6c5b5e138fffe95d6dcabdedb9.1763460113.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Following the extraction of sysfs code, this patch moves the sysctl
interface implementation into a dedicated file to further improve code
organization and maintainability of the hugetlb subsystem.
The following components are moved to mm/hugetlb_sysctl.c:
- proc_hugetlb_doulongvec_minmax()
- hugetlb_sysctl_handler_common()
- hugetlb_sysctl_handler()
- hugetlb_mempolicy_sysctl_handler() (CONFIG_NUMA)
- hugetlb_overcommit_handler()
- hugetlb_table[] sysctl table definition
- hugetlb_sysctl_init()
The hugetlb_internal.h header file is updated to declare the sysctl
initialization function with proper #ifdef guards for configurations
without CONFIG_SYSCTL support.
The Makefile is updated to compile hugetlb_sysctl.o when CONFIG_HUGETLBFS
is enabled. This refactoring reduces the size of hugetlb.c and logically
separates the sysctl interface from core hugetlb management code.
MAINTAINERS is updated to add new file hugetlb_sysctl.c.
No functional changes are introduced; all code is moved as-is from
hugetlb.c with consistent formatting.
Link: https://lkml.kernel.org/r/5bbee7ab5be71d0bb1aebec38642d7e83526bb7a.1762398359.git.zhuhui@kylinos.cn
Signed-off-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
Cc: David Hildenbrand <david@redhat.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm/hugetlb: refactor sysfs/sysctl interfaces", v5.
hugetlb.c has grown significantly and become difficult to maintain. This
patch series extracts the sysfs and sysctl interface code into separate
dedicated files to improve code organization.
The refactoring includes:
- Patch 1: Extract sysfs interface into mm/hugetlb_sysfs.c
- Patch 2: Extract sysctl interface into mm/hugetlb_sysctl.c
No functional changes are introduced in this series. The code is moved
as-is, with only minor formatting adjustments for code style consistency.
This should make future maintenance and enhancements to the hugetlb
subsystem easier.
Testing: The patch series has been compile-tested and maintains the same
functionality as the original code.
This patch (of 2):
Currently, hugetlb.c contains both core management logic and sysfs
interface implementations, making it difficult to maintain. This patch
extracts the sysfs-related code into a dedicated file to improve code
organization.
The following components are moved to mm/hugetlb_sysfs.c:
- sysfs attribute definitions and handlers
- sysfs kobject management functions
- NUMA per-node hstate attribute registration
Several inline helper functions and macros are moved to
mm/hugetlb_internal.h:
- hstate_is_gigantic_no_runtime()
- next_node_allowed()
- get_valid_node_allowed()
- hstate_next_node_to_alloc()
- hstate_next_node_to_free()
- for_each_node_mask_to_alloc/to_free macros
To support code sharing, these functions are changed from static to
exported symbols:
- remove_hugetlb_folio()
- add_hugetlb_folio()
- init_new_hugetlb_folio()
- prep_and_add_allocated_folios()
- demote_pool_huge_page()
- __nr_hugepages_store_common()
The Makefile is updated to compile hugetlb_sysfs.o when CONFIG_HUGETLBFS
is enabled. This maintains all existing functionality while improving
maintainability by separating concerns.
MAINTAINERS is updated to add new file hugetlb_sysfs.c.
Link: https://lkml.kernel.org/r/cover.1762398359.git.zhuhui@kylinos.cn
Link: https://lkml.kernel.org/r/656a03dff7e2bb20e24e841ede81fdca01d21410.1762398359.git.zhuhui@kylinos.cn
Signed-off-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
Cc: David Hildenbrand <david@redhat.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
