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| author | Gerald Schaefer <gerald.schaefer@linux.ibm.com> | 2025-07-09 20:34:30 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-08-15 16:39:34 +0200 |
| commit | db89c0e0f64e0d4e6f491c5eb9bd6fe4810aba66 (patch) | |
| tree | e0a1131037e110eb7e1235cf058720ab61d38873 | |
| parent | c7c87046b41a9ef28ee7ac476c369da5b5228bc5 (diff) | |
s390/mm: Remove possible false-positive warning in pte_free_defer()
commit 5647f61ad9171e8f025558ed6dc5702c56a33ba3 upstream.
Commit 8211dad627981 ("s390: add pte_free_defer() for pgtables sharing
page") added a warning to pte_free_defer(), on our request. It was meant
to warn if this would ever be reached for KVM guest mappings, because
the page table would be freed w/o a gmap_unlink(). THP mappings are not
allowed for KVM guests on s390, so this should never happen.
However, it is possible that the warning is triggered in a valid case as
false-positive.
s390_enable_sie() takes the mmap_lock, marks all VMAs as VM_NOHUGEPAGE and
splits possibly existing THP guest mappings. mm->context.has_pgste is set
to 1 before that, to prevent races with the mm_has_pgste() check in
MADV_HUGEPAGE.
khugepaged drops the mmap_lock for file mappings and might run in parallel,
before a vma is marked VM_NOHUGEPAGE, but after mm->context.has_pgste was
set to 1. If it finds file mappings to collapse, it will eventually call
pte_free_defer(). This will trigger the warning, but it is a valid case
because gmap is not yet set up, and the THP mappings will be split again.
Therefore, remove the warning and the comment.
Fixes: 8211dad627981 ("s390: add pte_free_defer() for pgtables sharing page")
Cc: <stable@vger.kernel.org> # 6.6+
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | arch/s390/mm/pgalloc.c | 5 |
1 files changed, 0 insertions, 5 deletions
diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c index b449fd2605b0..d2f6f1f6d2fc 100644 --- a/arch/s390/mm/pgalloc.c +++ b/arch/s390/mm/pgalloc.c @@ -173,11 +173,6 @@ void pte_free_defer(struct mm_struct *mm, pgtable_t pgtable) struct ptdesc *ptdesc = virt_to_ptdesc(pgtable); call_rcu(&ptdesc->pt_rcu_head, pte_free_now); - /* - * THPs are not allowed for KVM guests. Warn if pgste ever reaches here. - * Turn to the generic pte_free_defer() version once gmap is removed. - */ - WARN_ON_ONCE(mm_has_pgste(mm)); } #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ |