Postpone checking the VMA_LOCK flag until we've attempted to handle faults
on PUDs.  There's a mild upside to this patch in that we'll allocate the
page tables while under the VMA lock rather than the mmap lock, reducing
the hold time on the mmap lock, since the retry will find the page tables
already populated.  The real purpose here is to make a commit that shows
we don't call ->huge_fault under the VMA lock.  We do now handle setting
the accessed bit on a PUD fault under the VMA lock, but that doesn't seem
likely to be a measurable difference.

Link: https://lkml.kernel.org/r/20230724185410.1124082-5-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Arjun Roy <arjunroy@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Punit Agrawal <punit.agrawal@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Handle a little more of the page fault path outside the mmap sem.  The
hugetlb path doesn't need to check whether the VMA is anonymous; the
VM_HUGETLB flag is only set on hugetlbfs VMAs.  There should be no
performance change from the previous commit; this is simply a step to ease
bisection of any problems.

Link: https://lkml.kernel.org/r/20230724185410.1124082-4-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Cc: Arjun Roy <arjunroy@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Punit Agrawal <punit.agrawal@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Remove the TCP layering violation by allowing per-VMA locks on all VMAs. 
The fault path will immediately fail in handle_mm_fault().  There may be a
small performance reduction from this patch as a little unnecessary work
will be done on each page fault.  See later patches for the improvement.

Link: https://lkml.kernel.org/r/20230724185410.1124082-3-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Cc: Arjun Roy <arjunroy@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Punit Agrawal <punit.agrawal@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Patch series "Handle most file-backed faults under the VMA lock", v3.

This patchset adds the ability to handle page faults on parts of files
which are already in the page cache without taking the mmap lock.


This patch (of 10):

Provide lock_vma_under_rcu() when CONFIG_PER_VMA_LOCK is not defined to
eliminate ifdefs in the users.

Link: https://lkml.kernel.org/r/20230724185410.1124082-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20230724185410.1124082-2-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Cc: Punit Agrawal <punit.agrawal@bytedance.com>
Cc: Arjun Roy <arjunroy@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

By delaying the setting of prev/next VMA until after the write of NULL,
the probability of the prev/next VMA already being in the CPU cache is
significantly increased, especially for larger munmap operations.  It
also means that prev/next will be loaded closer to when they are used.

This requires changing the loop type when gathering the VMAs that will
be freed.

Since prev will be set later in the function, it is better to reverse
the splitting direction of the start VMA (modify the new_below argument
to __split_vma).

Using the vma_iter_prev_range() to walk back to the correct location in
the tree will, on the most part, mean walking within the CPU cache.
Usually, this is two steps vs a node reset and a tree re-walk.

Link: https://lkml.kernel.org/r/20230724183157.3939892-16-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mas_prealloc() may walk partially down the tree before finding that a
split or spanning store is needed.  When the write occurs, relax the
logic on resetting the walk so that partial walks will not restart, but
walks that have gone too far (a store that affects beyond the current
node) should be restarted.

Link: https://lkml.kernel.org/r/20230724183157.3939892-15-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Calculate the number of nodes based on the pending write action instead
of assuming the worst case.

This addresses a performance regression introduced in platforms that
have longer allocation timing.

Link: https://lkml.kernel.org/r/20230724183157.3939892-14-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Since the mas_preallocate() calculation has been updated to be more
precise, the testing must also be updated to check for what is expected.

Link: https://lkml.kernel.org/r/20230724183157.3939892-13-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Relocate it and call mas_wr_extend_null() from within mas_wr_end_piv().
Extending the NULL may affect the end pivot value so call
mas_wr_endtend_null() from within mas_wr_end_piv() to keep it all
together.

Link: https://lkml.kernel.org/r/20230724183157.3939892-12-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Set the correct limits for vma_iter_prealloc() calls so that the maple
tree can be smarter about how many nodes are needed.

Link: https://lkml.kernel.org/r/20230724183157.3939892-11-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Move the definition of vma_iter_clear_gfp() from mmap.c to internal.h so
it can be used in the nommu code.  This will reduce node preallocations
in nommu.

Link: https://lkml.kernel.org/r/20230724183157.3939892-10-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mas_rebalance() is called to rebalance an insufficient node into a
single node or two sufficient nodes.  The preallocation estimate is
always too many in this case as the height of the tree will never grow
and there is no possibility to have a three way split in this case, so
revise the node allocation count.

Link: https://lkml.kernel.org/r/20230724183157.3939892-9-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

The current preallocation strategy is to preallocate the absolute
worst-case allocation for a tree modification.  The entry (or NULL) is
needed to know how many nodes are needed to write to the tree.  Start by
adding the argument to the mas_preallocate() definition.

Link: https://lkml.kernel.org/r/20230724183157.3939892-8-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Using vma_iter_set() will reset the tree and cause a re-walk.  Use
vmi_iter_config() to set the write to a sub-set of the range.  Change
the file case to also use vmi_iter_config() so that the end is correctly
set.

Link: https://lkml.kernel.org/r/20230724183157.3939892-7-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mas_set_range() resets the node to MAS_START, which will cause a re-walk
of the tree to the range.  This is unnecessary when the maple state is
already at the correct location of the write.  Add a function that only
sets the range to avoid unnecessary re-walking of the tree.

Link: https://lkml.kernel.org/r/20230724183157.3939892-6-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

If the prev does not exist, the vma iterator will be set to MAS_NONE,
which will be treated as a MAS_START when the mas_next or mas_find is
used.  In this case, the next caller will be the vma iterator, which
uses mas_find() under the hood and will now do what the user expects.

Link: https://lkml.kernel.org/r/20230724183157.3939892-5-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

The majority of the calls to munmap a vm range is within a single vma.
The maple tree is able to store a single entry at 0, with a size of 1 as
a pointer and avoid any allocations.  Change do_vmi_align_munmap() to
store the VMAs being munmap()'ed into a tree indexed by the count.  This
will leverage the ability to store the first entry without a node
allocation.

Storing the entries into a tree by the count and not the vma start and
end means changing the functions which iterate over the entries.  Update
unmap_vmas() and free_pgtables() to take a maple state and a tree end
address to support this functionality.

Passing through the same maple state to unmap_vmas() and free_pgtables()
means the state needs to be reset between calls.  This happens in the
static unmap_region() and exit_mmap().

Link: https://lkml.kernel.org/r/20230724183157.3939892-4-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Add some benchmarking functions in testing for mas_prev().  This is
useful to ensure there are no regressions added during modifications.

Link: https://lkml.kernel.org/r/20230724183157.3939892-3-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Patch series "Reduce preallocations for maple tree", v3.

Initial work on preallocations showed no regression in performance during
testing, but recently some users (both on [1] and off [android] list) have
reported that preallocating the worst-case number of nodes has caused some
slow down.  This patch set addresses the number of allocations in a few
ways.

During munmap() most munmap() operations will remove a single VMA, so
leverage the fact that the maple tree can place a single pointer at range
0 - 0 without allocating.  This is done by changing the index of the VMAs
to be indexed by the count, starting at 0.

Re-introduce the entry argument to mas_preallocate() so that a more
intelligent guess of the node count can be made.

Implement the more intelligent guess of the node count, although there is
more work to be done.

During development of v2 of this patch set, I also noticed that the number
of nodes being allocated for a rebalance was beyond what could possibly be
needed.  This is addressed in patch 0008.


This patch (of 15):

Add a way to test the speed of mas_for_each() to the testing code.

Link: https://lkml.kernel.org/r/20230724183157.3939892-1-Liam.Howlett@oracle.com
Link: https://lkml.kernel.org/r/20230724183157.3939892-2-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Despite its name, mm_drop_all_locks() does not drop _all_ locks; the mmap
lock is held write-locked by the caller, and the caller is responsible for
dropping the mmap lock at a later point (which will also release the VMA
locks).

Calling vma_end_write_all() here is dangerous because the caller might
have write-locked a VMA with the expectation that it will stay
write-locked until the mmap_lock is released, as usual.

This _almost_ becomes a problem in the following scenario:

An anonymous VMA A and an SGX VMA B are mapped adjacent to each other. 
Userspace calls munmap() on a range starting at the start address of A and
ending in the middle of B.

Hypothetical call graph with additional notes in brackets:

do_vmi_align_munmap
  [begin first for_each_vma_range loop]
  vma_start_write [on VMA A]
  vma_mark_detached [on VMA A]
  __split_vma [on VMA B]
    sgx_vma_open [== new->vm_ops->open]
      sgx_encl_mm_add
        __mmu_notifier_register [luckily THIS CAN'T ACTUALLY HAPPEN]
          mm_take_all_locks
          mm_drop_all_locks
            vma_end_write_all [drops VMA lock taken on VMA A before]
  vma_start_write [on VMA B]
  vma_mark_detached [on VMA B]
  [end first for_each_vma_range loop]
  vma_iter_clear_gfp [removes VMAs from maple tree]
  mmap_write_downgrade
  unmap_region
  mmap_read_unlock

In this hypothetical scenario, while do_vmi_align_munmap() thinks it still
holds a VMA write lock on VMA A, the VMA write lock has actually been
invalidated inside __split_vma().

The call from sgx_encl_mm_add() to __mmu_notifier_register() can't
actually happen here, as far as I understand, because we are duplicating
an existing SGX VMA, but sgx_encl_mm_add() only calls
__mmu_notifier_register() for the first SGX VMA created in a given
process.  So this could only happen in fork(), not on munmap().  But in my
view it is just pure luck that this can't happen.

Also, we wouldn't actually have any bad consequences from this in
do_vmi_align_munmap(), because by the time the bug drops the lock on VMA
A, we've already marked VMA A as detached, which makes it completely
ineligible for any VMA-locked page faults.  But again, that's just pure
luck.

So remove the vma_end_write_all(), so that VMA write locks are only ever
released on mmap_write_unlock() or mmap_write_downgrade().

Also add comments to document the locking rules established by this patch.

Link: https://lkml.kernel.org/r/20230720193436.454247-1-jannh@google.com
Fixes: eeff9a5d ("mm/mmap: prevent pagefault handler from racing with mmu_notifier registration")
Signed-off-by: Jann Horn <jannh@google.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Convert bio_associate_blkg_from_page() to take in a folio. We can remove
two implicit calls to compound_head() by taking in a folio.

Link: https://lkml.kernel.org/r/20230721034451.16412-11-zhangpeng362@huawei.comSigned-off-by: ZhangPeng <zhangpeng362@huawei.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Convert count_swpout_vm_event() to take in a folio. We can remove five
implicit calls to compound_head() by taking in a folio.

Link: https://lkml.kernel.org/r/20230721034451.16412-10-zhangpeng362@huawei.comSigned-off-by: ZhangPeng <zhangpeng362@huawei.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Saves one implicit call to compound_head().

Link: https://lkml.kernel.org/r/20230721034451.16412-9-zhangpeng362@huawei.comSigned-off-by: ZhangPeng <zhangpeng362@huawei.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Saves one implicit call to compound_head().

Link: https://lkml.kernel.org/r/20230721034451.16412-8-zhangpeng362@huawei.comSigned-off-by: ZhangPeng <zhangpeng362@huawei.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Saves one implicit call to compound_head().

Link: https://lkml.kernel.org/r/20230721034451.16412-7-zhangpeng362@huawei.comSigned-off-by: ZhangPeng <zhangpeng362@huawei.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Saves one implicit call to compound_head().

Link: https://lkml.kernel.org/r/20230721034451.16412-6-zhangpeng362@huawei.comSigned-off-by: ZhangPeng <zhangpeng362@huawei.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Saves two implicit call to compound_head().

Link: https://lkml.kernel.org/r/20230721034451.16412-5-zhangpeng362@huawei.comSigned-off-by: ZhangPeng <zhangpeng362@huawei.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Introduce bio_first_folio_all() to return a folio, which makes it easier
to use.

Link: https://lkml.kernel.org/r/20230721034451.16412-4-zhangpeng362@huawei.comSigned-off-by: ZhangPeng <zhangpeng362@huawei.com>
Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Nobody checks the PageError()/folio_test_error() for the page/folio in
__end_swap_bio_read/write() and sio_write_complete(). Therefore, we
don't need to set the error flag. Just drop it.

Link: https://lkml.kernel.org/r/20230721034451.16412-3-zhangpeng362@huawei.comSigned-off-by: ZhangPeng <zhangpeng362@huawei.com>
Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Patch series "Convert several functions in page_io.c to use a folio", v4.

Convert several functions in page_io.c to use a folio, which can remove
several implicit calls to compound_head().


This patch (of 10):

The VM_BUG_ON_FOLIO in swap_readpage() ensures that the page is already
!uptodate in __end_swap_bio_read() and sio_read_complete().  Just remove
unneeded ClearPageUptodate().

Link: https://lkml.kernel.org/r/20230721034451.16412-1-zhangpeng362@huawei.com
Link: https://lkml.kernel.org/r/20230721034451.16412-2-zhangpeng362@huawei.comSigned-off-by: ZhangPeng <zhangpeng362@huawei.com>
Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Move pageblock_end_pfn after no_set_skip_hint check to avoid unneeded
pageblock_end_pfn if no_set_skip_hint is set.

Link: https://lkml.kernel.org/r/20230721150957.2058634-3-shikemeng@huawei.comSigned-off-by: Kemeng Shi <shikemeng@huawei.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Patch series "Two minor cleanups for compaction", v2.

This series contains two random cleanups for compaction.


This patch (of 2):

If no preferred one was not found, we will use candidate page with maximum
pfn > min_pfn which is saved in high_pfn.  Correct "minimum" to "maximum
candidate" in comment.

Link: https://lkml.kernel.org/r/20230721150957.2058634-1-shikemeng@huawei.com
Link: https://lkml.kernel.org/r/20230721150957.2058634-2-shikemeng@huawei.comSigned-off-by: Kemeng Shi <shikemeng@huawei.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Since commit 79a1971c ("mm: move the copy_one_pte() pte_present check
into the caller"), the explanation of preserving soft-dirtiness is moved
into copy_nonpresent_pte().  Update corresponding comment.

Link: https://lkml.kernel.org/r/20230723033114.3224409-1-linmiaohe@huawei.comSigned-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

It is very unclear to me how one is supposed to run all the mm selftests
consistently and get clear results.

Most of the test programs are launched by both run_vmtests.sh and
run_kselftest.sh:

  hugepage-mmap
  hugepage-shm
  map_hugetlb
  hugepage-mremap
  hugepage-vmemmap
  hugetlb-madvise
  map_fixed_noreplace
  gup_test
  gup_longterm
  uffd-unit-tests
  uffd-stress
  compaction_test
  on-fault-limit
  map_populate
  mlock-random-test
  mlock2-tests
  mrelease_test
  mremap_test
  thuge-gen
  virtual_address_range
  va_high_addr_switch
  mremap_dontunmap
  hmm-tests
  madv_populate
  memfd_secret
  ksm_tests
  ksm_functional_tests
  soft-dirty
  cow

However, of this set, when launched by run_vmtests.sh, some of the
programs are invoked multiple times with different arguments. When
invoked by run_kselftest.sh, they are invoked without arguments (and as
a consequence, some fail immediately).

Some test programs are only launched by run_vmtests.sh:

  test_vmalloc.sh

And some test programs and only launched by run_kselftest.sh:

  khugepaged
  migration
  mkdirty
  transhuge-stress
  split_huge_page_test
  mdwe_test
  write_to_hugetlbfs

Furthermore, run_vmtests.sh is invoked by run_kselftest.sh, so in this
case all the test programs invoked by both scripts are run twice!

Needless to say, this is a bit of a mess. In the absence of fully
understanding the history here, it looks to me like the best solution is
to launch ALL test programs from run_vmtests.sh, and ONLY invoke
run_vmtests.sh from run_kselftest.sh. This way, we get full control over
the parameters, each program is only invoked the intended number of
times, and regardless of which script is used, the same tests get run in
the same way.

The only drawback is that if using run_kselftest.sh, it's top-level tap
result reporting reports only a single test and it fails if any of the
contained tests fail. I don't see this as a big deal though since we
still see all the nested reporting from multiple layers. The other issue
with this is that all of run_vmtests.sh must execute within a single
kselftest timeout period, so let's increase that to something more
suitable.

In the Makefile, TEST_GEN_PROGS will compile and install the tests and
will add them to the list of tests that run_kselftest.sh will run.
TEST_GEN_FILES will compile and install the tests but will not add them
to the test list. So let's move all the programs from TEST_GEN_PROGS to
TEST_GEN_FILES so that they are built but not executed by
run_kselftest.sh. Note that run_vmtests.sh is added to TEST_PROGS, which
means it ends up in the test list. (the lack of "_GEN" means it won't be
compiled, but simply copied).

Link: https://lkml.kernel.org/r/20230724082522.1202616-9-ryan.roberts@arm.comSigned-off-by: Ryan Roberts <ryan.roberts@arm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Peter Xu <peterx@redhat.com>
Cc: Florent Revest <revest@chromium.org>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Until now, transhuge-stress runs until its explicitly killed, so when
invoked by run_kselftest.sh, it would run until the test timeout, then it
would be killed and the test would be marked as failed.

Add a new, optional command line parameter that allows the user to specify
the duration in seconds that the program should run.  The program exits
after this duration with a success (0) exit code.  If the argument is
omitted the old behacvior remains.

On it's own, this doesn't quite solve our problem because run_kselftest.sh
does not allow passing parameters to the program under test.  But we will
shortly move this to run_vmtests.sh, which does allow parameter passing.

Link: https://lkml.kernel.org/r/20230724082522.1202616-8-ryan.roberts@arm.comSigned-off-by: Ryan Roberts <ryan.roberts@arm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Florent Revest <revest@chromium.org>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

The `migration` test currently has a number of robustness problems that
cause it to hang and leak resources.

Timeout: There are 3 tests, which each previously ran for 60 seconds. 
However, the timeout in mm/settings for a single test binary was set to 45
seconds.  So when run using run_kselftest.sh, the top level timeout would
trigger before the test binary was finished.  Solve this by meeting in the
middle; each of the 3 tests now runs for 20 seconds (for a total of 60),
and the top level timeout is set to 90 seconds.

Leaking child processes: the `shared_anon` test fork()s some children but
then an ASSERT() fires before the test kills those children.  The assert
causes immediate exit of the parent and leaking of the children. 
Furthermore, if run using the run_kselftest.sh wrapper, the wrapper would
get stuck waiting for those children to exit, which never happens.  Solve
this by setting the "parent death signal" to SIGHUP in the child, so that
the child is killed automatically if the parent dies.

With these changes, the test binary now runs to completion on arm64, with
2 tests passing and the `shared_anon` test failing.

Link: https://lkml.kernel.org/r/20230724082522.1202616-7-ryan.roberts@arm.comSigned-off-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Florent Revest <revest@chromium.org>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

va_high_addr_switch has a mechanism to determine if the tests should be
run or skipped (supported_arch()).  This currently returns unconditionally
true for arm64.  However, va_high_addr_switch also requires a large
virtual address space for the tests to run, otherwise they spuriously
fail.

Since arm64 can only support VA > 48 bits when the page size is 64K, let's
decide whether we should skip the test suite based on the page size.  This
reduces noise when running on 4K and 16K kernels.

Link: https://lkml.kernel.org/r/20230724082522.1202616-6-ryan.roberts@arm.comSigned-off-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Florent Revest <revest@chromium.org>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

thuge-gen was previously only munmapping part of the mmapped buffer, which
caused us to run out of 1G huge pages for a later part of the test.  Fix
this by munmapping the whole buffer.  Based on the code, it looks like a
typo rather than an intention to keep some of the buffer mapped.

thuge-gen was also calling mmap with SHM_HUGETLB flag (bit 11 set), which
is actually MAP_DENYWRITE in mmap context.  The man page says this flag is
ignored in modern kernels.  I'm pretty sure from the context that the
author intended to pass the MAP_HUGETLB flag so I've fixed that up too.

Link: https://lkml.kernel.org/r/20230724082522.1202616-5-ryan.roberts@arm.comSigned-off-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Florent Revest <revest@chromium.org>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mrelease_test defaults to defining __NR_pidfd_open and
__NR_process_mrelease syscall numbers to -1, if they are not defined
anywhere else, and the suite would then be marked as skipped as a result.

arm64 (at least the stock debian toolchain that I'm using) requires
including <sys/syscall.h> to pull in the defines for these syscalls.  So
let's add this header.  With this in place, the test is passing on arm64.

Link: https://lkml.kernel.org/r/20230724082522.1202616-4-ryan.roberts@arm.comSigned-off-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Florent Revest <revest@chromium.org>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arm64 does not support the soft-dirty PTE bit.  However, the `soft-dirty`
test suite is currently run unconditionally and therefore generates
spurious test failures on arm64.  There are also some tests in
`madv_populate` which assume it is supported.

For `soft-dirty` lets disable the whole suite for arm64; it is no longer
built and run_vmtests.sh will skip it if its not present.

For `madv_populate`, we need a runtime mechanism so that the remaining
tests continue to be run.  Unfortunately, the only way to determine if the
soft-dirty dirty bit is supported is to write to a page, then see if the
bit is set in /proc/self/pagemap.  But the tests that we want to
conditionally execute are testing precicesly this.  So if we introduced
this feature check, we could accedentally turn a real failure (on a system
that claims to support soft-dirty) into a skip.  So instead, do the check
based on architecture; for arm64, we report that soft-dirty is not
supported.

Link: https://lkml.kernel.org/r/20230724082522.1202616-3-ryan.roberts@arm.comSigned-off-by: Ryan Roberts <ryan.roberts@arm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Florent Revest <revest@chromium.org>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>