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@xxxxxxxxxxxxxxxxx>
> Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> ---
> 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@xxxxxxxxxx>
--
Thanks,
David / dhildenb
