Re: [PATCH v1 1/9] mm/memory: factor out zapping of present pte into zap_present_pte()

Ryan Roberts
2024-01-30T08:13:45Z

On 29/01/2024 14:32, David Hildenbrand wrote:
> Let's prepare for further changes by factoring out processing of present
> PTEs.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> mm/memory.c | 92 ++++++++++++++++++++++++++++++-----------------------
> 1 file changed, 52 insertions(+), 40 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index b05fd28dbce1..50a6c79c78fc 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1532,13 +1532,61 @@ zap_install_uffd_wp_if_needed(struct vm_area_struct *vma,
> pte_install_uffd_wp_if_needed(vma, addr, pte, pteval);
> }
>
> +static inline void zap_present_pte(struct mmu_gather *tlb,
> + struct vm_area_struct *vma, pte_t *pte, pte_t ptent,
> + unsigned long addr, struct zap_details *details,
> + int *rss, bool *force_flush, bool *force_break)
> +{
> + struct mm_struct *mm = tlb->mm;
> + bool delay_rmap = false;
> + struct folio *folio;

You need to init this to NULL otherwise its a random value when calling
should_zap_folio() if vm_normal_page() returns NULL.

> + struct page *page;
> +
> + page = vm_normal_page(vma, addr, ptent);
> + if (page)
> + folio = page_folio(page);
> +
> + if (unlikely(!should_zap_folio(details, folio)))
> + return;
> + ptent = ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm);
> + arch_check_zapped_pte(vma, ptent);
> + tlb_remove_tlb_entry(tlb, pte, addr);
> + zap_install_uffd_wp_if_needed(vma, addr, pte, details, ptent);
> + if (unlikely(!page)) {
> + ksm_might_unmap_zero_page(mm, ptent);
> + return;
> + }
> +
> + if (!folio_test_anon(folio)) {
> + if (pte_dirty(ptent)) {
> + folio_mark_dirty(folio);
> + if (tlb_delay_rmap(tlb)) {
> + delay_rmap = true;
> + *force_flush = true;
> + }
> + }
> + if (pte_young(ptent) && likely(vma_has_recency(vma)))
> + folio_mark_accessed(folio);
> + }
> + rss[mm_counter(folio)]--;
> + if (!delay_rmap) {
> + folio_remove_rmap_pte(folio, page, vma);
> + if (unlikely(page_mapcount(page) < 0))
> + print_bad_pte(vma, addr, ptent, page);
> + }
> + if (unlikely(__tlb_remove_page(tlb, page, delay_rmap))) {
> + *force_flush = true;
> + *force_break = true;
> + }
> +}
> +
> static unsigned long zap_pte_range(struct mmu_gather *tlb,
> struct vm_area_struct *vma, pmd_t *pmd,
> unsigned long addr, unsigned long end,
> struct zap_details *details)
> {
> + bool force_flush = false, force_break = false;
> struct mm_struct *mm = tlb->mm;
> - int force_flush = 0;
> int rss[NR_MM_COUNTERS];
> spinlock_t *ptl;
> pte_t *start_pte;
> @@ -1565,45 +1613,9 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
> break;
>
> if (pte_present(ptent)) {
> - unsigned int delay_rmap;
> -
> - page = vm_normal_page(vma, addr, ptent);
> - if (page)
> - folio = page_folio(page);
> -
> - if (unlikely(!should_zap_folio(details, folio)))
> - continue;
> - ptent = ptep_get_and_clear_full(mm, addr, pte,
> - tlb->fullmm);
> - arch_check_zapped_pte(vma, ptent);
> - tlb_remove_tlb_entry(tlb, pte, addr);
> - zap_install_uffd_wp_if_needed(vma, addr, pte, details,
> - ptent);
> - if (unlikely(!page)) {
> - ksm_might_unmap_zero_page(mm, ptent);
> - continue;
> - }
> -
> - delay_rmap = 0;
> - if (!folio_test_anon(folio)) {
> - if (pte_dirty(ptent)) {
> - folio_mark_dirty(folio);
> - if (tlb_delay_rmap(tlb)) {
> - delay_rmap = 1;
> - force_flush = 1;
> - }
> - }
> - if (pte_young(ptent) && likely(vma_has_recency(vma)))
> - folio_mark_accessed(folio);
> - }
> - rss[mm_counter(folio)]--;
> - if (!delay_rmap) {
> - folio_remove_rmap_pte(folio, page, vma);
> - if (unlikely(page_mapcount(page) < 0))
> - print_bad_pte(vma, addr, ptent, page);
> - }
> - if (unlikely(__tlb_remove_page(tlb, page, delay_rmap))) {
> - force_flush = 1;
> + zap_present_pte(tlb, vma, pte, ptent, addr, details,
> + rss, &force_flush, &force_break);
> + if (unlikely(force_break)) {
> addr += PAGE_SIZE;
> break;
> }