@@ -316,6 +316,37 @@ static int mfill_atomic_pte_copy(pmd_t *dst_pmd,
goto out;
}
+static int mfill_atomic_pte_zeroed_folio(pmd_t *dst_pmd,
+ struct vm_area_struct *dst_vma, unsigned long dst_addr)
+{
+ struct folio *folio;
+ int ret = -ENOMEM;
+
+ folio = vma_alloc_zeroed_movable_folio(dst_vma, dst_addr);
+ if (!folio)
+ return ret;
+
+ if (mem_cgroup_charge(folio, dst_vma->vm_mm, GFP_KERNEL))
+ goto out_put;
+
+ /*
+ * The memory barrier inside __folio_mark_uptodate makes sure that
+ * zeroing out the folio become visible before mapping the page
+ * using set_pte_at(). See do_anonymous_page().
+ */
+ __folio_mark_uptodate(folio);
+
+ ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,
+ &folio->page, true, 0);
+ if (ret)
+ goto out_put;
+
+ return 0;
+out_put:
+ folio_put(folio);
+ return ret;
+}
+
static int mfill_atomic_pte_zeropage(pmd_t *dst_pmd,
struct vm_area_struct *dst_vma,
unsigned long dst_addr)
@@ -324,6 +355,9 @@ static int mfill_atomic_pte_zeropage(pmd_t *dst_pmd,
spinlock_t *ptl;
int ret;
+ if (mm_forbids_zeropage(dst_vma->vm_mm))
+ return mfill_atomic_pte_zeroed_folio(dst_pmd, dst_vma, dst_addr);
+
_dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
dst_vma->vm_page_prot));
ret = -EAGAIN;
s390x must disable shared zeropages for processes running VMs, because the VMs could end up making use of "storage keys" or protected virtualization, which are incompatible with shared zeropages. Yet, with userfaultfd it is possible to insert shared zeropages into such processes. Let's fallback to simply allocating a fresh zeroed anonymous folio and insert that instead. mm_forbids_zeropage() was introduced in commit 593befa6ab74 ("mm: introduce mm_forbids_zeropage function"), briefly before userfaultfd went upstream. Note that we don't want to fail the UFFDIO_ZEROPAGE request like we do for hugetlb, it would be rather unexpected. Further, we also cannot really indicated "not supported" to user space ahead of time: it could be that the MM disallows zeropages after userfaultfd was already registered. Fixes: c1a4de99fada ("userfaultfd: mcopy_atomic|mfill_zeropage: UFFDIO_COPY|UFFDIO_ZEROPAGE preparation") Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> --- mm/userfaultfd.c | 34 ++++++++++++++++++++++++++++++++++ 1 file changed, 34 insertions(+)