6.15-stable review patch. If anyone has any objections, please let me know.
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From: Gerald Schaefer gerald.schaefer@linux.ibm.com
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 --- arch/s390/mm/pgalloc.c | 5 ----- 1 file changed, 5 deletions(-)
--- a/arch/s390/mm/pgalloc.c +++ b/arch/s390/mm/pgalloc.c @@ -176,11 +176,6 @@ void pte_free_defer(struct mm_struct *mm 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 */