| Message ID | 0a2e547238cad5bc153a85c3e9658cb9d55f9cac.1652270205.git.baolin.wang@linux.alibaba.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | Fix CONT-PTE/PMD size hugetlb issue when unmapping or migrating | expand |
On 11.05.22 14:04, Baolin Wang wrote: > On some architectures (like ARM64), it can support CONT-PTE/PMD size > hugetlb, which means it can support not only PMD/PUD size hugetlb: > 2M and 1G, but also CONT-PTE/PMD size: 64K and 32M if a 4K page > size specified. > > When unmapping a hugetlb page, we will get the relevant page table > entry by huge_pte_offset() only once to nuke it. This is correct > for PMD or PUD size hugetlb, since they always contain only one > pmd entry or pud entry in the page table. > > However this is incorrect for CONT-PTE and CONT-PMD size hugetlb, > since they can contain several continuous pte or pmd entry with > same page table attributes, so we will nuke only one pte or pmd > entry for this CONT-PTE/PMD size hugetlb page. > > And now try_to_unmap() is only passed a hugetlb page in the case > where the hugetlb page is poisoned. Which means now we will unmap > only one pte entry for a CONT-PTE or CONT-PMD size poisoned hugetlb > page, and we can still access other subpages of a CONT-PTE or CONT-PMD > size poisoned hugetlb page, which will cause serious issues possibly. > > So we should change to use huge_ptep_clear_flush() to nuke the > hugetlb page table to fix this issue, which already considered > CONT-PTE and CONT-PMD size hugetlb. > > We've already used set_huge_swap_pte_at() to set a poisoned > swap entry for a poisoned hugetlb page. Meanwhile adding a VM_BUG_ON() > to make sure the passed hugetlb page is poisoned in try_to_unmap(). > > Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> > Reviewed-by: Muchun Song <songmuchun@bytedance.com> > Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com> > --- > mm/rmap.c | 39 ++++++++++++++++++++++----------------- > 1 file changed, 22 insertions(+), 17 deletions(-) > > diff --git a/mm/rmap.c b/mm/rmap.c > index 4e96daf..219e287 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1528,6 +1528,11 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > > if (folio_test_hugetlb(folio)) { > /* > + * The try_to_unmap() is only passed a hugetlb page > + * in the case where the hugetlb page is poisoned. > + */ > + VM_BUG_ON_PAGE(!PageHWPoison(subpage), subpage); > + /* > * huge_pmd_unshare may unmap an entire PMD page. > * There is no way of knowing exactly which PMDs may > * be cached for this mm, so we must flush them all. > @@ -1562,28 +1567,28 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > break; > } > } > + pteval = huge_ptep_clear_flush(vma, address, pvmw.pte); > } else { > flush_cache_page(vma, address, pte_pfn(*pvmw.pte)); > - } > - > - /* > - * Nuke the page table entry. When having to clear > - * PageAnonExclusive(), we always have to flush. > - */ > - if (should_defer_flush(mm, flags) && !anon_exclusive) { > /* > - * We clear the PTE but do not flush so potentially > - * a remote CPU could still be writing to the folio. > - * If the entry was previously clean then the > - * architecture must guarantee that a clear->dirty > - * transition on a cached TLB entry is written through > - * and traps if the PTE is unmapped. > + * Nuke the page table entry. When having to clear > + * PageAnonExclusive(), we always have to flush. > */ > - pteval = ptep_get_and_clear(mm, address, pvmw.pte); > + if (should_defer_flush(mm, flags) && !anon_exclusive) { > + /* > + * We clear the PTE but do not flush so potentially > + * a remote CPU could still be writing to the folio. > + * If the entry was previously clean then the > + * architecture must guarantee that a clear->dirty > + * transition on a cached TLB entry is written through > + * and traps if the PTE is unmapped. > + */ > + pteval = ptep_get_and_clear(mm, address, pvmw.pte); > > - set_tlb_ubc_flush_pending(mm, pte_dirty(pteval)); > - } else { > - pteval = ptep_clear_flush(vma, address, pvmw.pte); > + set_tlb_ubc_flush_pending(mm, pte_dirty(pteval)); > + } else { > + pteval = ptep_clear_flush(vma, address, pvmw.pte); > + } > } > > /* LGTM Acked-by: David Hildenbrand <david@redhat.com>
diff --git a/mm/rmap.c b/mm/rmap.c index 4e96daf..219e287 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1528,6 +1528,11 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, if (folio_test_hugetlb(folio)) { /* + * The try_to_unmap() is only passed a hugetlb page + * in the case where the hugetlb page is poisoned. + */ + VM_BUG_ON_PAGE(!PageHWPoison(subpage), subpage); + /* * huge_pmd_unshare may unmap an entire PMD page. * There is no way of knowing exactly which PMDs may * be cached for this mm, so we must flush them all. @@ -1562,28 +1567,28 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, break; } } + pteval = huge_ptep_clear_flush(vma, address, pvmw.pte); } else { flush_cache_page(vma, address, pte_pfn(*pvmw.pte)); - } - - /* - * Nuke the page table entry. When having to clear - * PageAnonExclusive(), we always have to flush. - */ - if (should_defer_flush(mm, flags) && !anon_exclusive) { /* - * We clear the PTE but do not flush so potentially - * a remote CPU could still be writing to the folio. - * If the entry was previously clean then the - * architecture must guarantee that a clear->dirty - * transition on a cached TLB entry is written through - * and traps if the PTE is unmapped. + * Nuke the page table entry. When having to clear + * PageAnonExclusive(), we always have to flush. */ - pteval = ptep_get_and_clear(mm, address, pvmw.pte); + if (should_defer_flush(mm, flags) && !anon_exclusive) { + /* + * We clear the PTE but do not flush so potentially + * a remote CPU could still be writing to the folio. + * If the entry was previously clean then the + * architecture must guarantee that a clear->dirty + * transition on a cached TLB entry is written through + * and traps if the PTE is unmapped. + */ + pteval = ptep_get_and_clear(mm, address, pvmw.pte); - set_tlb_ubc_flush_pending(mm, pte_dirty(pteval)); - } else { - pteval = ptep_clear_flush(vma, address, pvmw.pte); + set_tlb_ubc_flush_pending(mm, pte_dirty(pteval)); + } else { + pteval = ptep_clear_flush(vma, address, pvmw.pte); + } } /*