On 2/3/2023 9:25 PM, David Hildenbrand wrote:
> On 03.02.23 14:16, Yin Fengwei wrote:
>> do_set_pte_range() allows to setup page table entries for a
>> specific range. It calls folio_add_file_rmap_range() to take
>> advantage of batched rmap update for large folio.
>>
>> Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
>> ---
>> include/linux/mm.h | 3 +++
>> mm/filemap.c | 1 -
>> mm/memory.c | 59 ++++++++++++++++++++++++++++++----------------
>> 3 files changed, 42 insertions(+), 21 deletions(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index d6f8f41514cc..93192f04b276 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -1162,6 +1162,9 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
>> vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page);
>> void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr);
>> +void do_set_pte_range(struct vm_fault *vmf, struct folio *folio,
>> + unsigned long addr, pte_t *pte,
>> + unsigned long start, unsigned int nr);
>> vm_fault_t finish_fault(struct vm_fault *vmf);
>> vm_fault_t finish_mkwrite_fault(struct vm_fault *vmf);
>> diff --git a/mm/filemap.c b/mm/filemap.c
>> index f444684db9f2..74046a3a0ff5 100644
>> --- a/mm/filemap.c
>> +++ b/mm/filemap.c
>> @@ -3386,7 +3386,6 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
>> ref_count++;
>> do_set_pte(vmf, page, addr);
>> - update_mmu_cache(vma, addr, vmf->pte);
>> } while (vmf->pte++, page++, addr += PAGE_SIZE, ++count < nr_pages);
>> /* Restore the vmf->pte */
>> diff --git a/mm/memory.c b/mm/memory.c
>> index 7a04a1130ec1..3754b2ef166a 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -4257,36 +4257,58 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
>> }
>> #endif
>> -void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr)
>> +void do_set_pte_range(struct vm_fault *vmf, struct folio *folio,
>> + unsigned long addr, pte_t *pte,
>> + unsigned long start, unsigned int nr)
>> {
>> struct vm_area_struct *vma = vmf->vma;
>> bool uffd_wp = pte_marker_uffd_wp(vmf->orig_pte);
>> bool write = vmf->flags & FAULT_FLAG_WRITE;
>> + bool cow = write && !(vma->vm_flags & VM_SHARED);
>> bool prefault = vmf->address != addr;
>> + struct page *page = folio_page(folio, start);
>> pte_t entry;
>> - flush_icache_page(vma, page);
>> - entry = mk_pte(page, vma->vm_page_prot);
>> + if (!cow) {
>> + folio_add_file_rmap_range(folio, start, nr, vma, false);
>> + add_mm_counter(vma->vm_mm, mm_counter_file(page), nr);
>> + }
>> - if (prefault && arch_wants_old_prefaulted_pte())
>> - entry = pte_mkold(entry);
>> - else
>> - entry = pte_sw_mkyoung(entry);
>> + do {
>> + flush_icache_page(vma, page);
>> + entry = mk_pte(page, vma->vm_page_prot);
>> - if (write)
>> - entry = maybe_mkwrite(pte_mkdirty(entry), vma);
>> - if (unlikely(uffd_wp))
>> - entry = pte_mkuffd_wp(entry);
>> - /* copy-on-write page */
>> - if (write && !(vma->vm_flags & VM_SHARED)) {
>> + if (prefault && arch_wants_old_prefaulted_pte())
>> + entry = pte_mkold(entry);
>> + else
>> + entry = pte_sw_mkyoung(entry);
>> +
>> + if (write)
>> + entry = maybe_mkwrite(pte_mkdirty(entry), vma);
>> + if (unlikely(uffd_wp))
>> + entry = pte_mkuffd_wp(entry);
>> + set_pte_at(vma->vm_mm, addr, pte, entry);
>> +
>> + /* no need to invalidate: a not-present page won't be cached */
>> + update_mmu_cache(vma, addr, pte);
>> + } while (pte++, page++, addr += PAGE_SIZE, --nr > 0);
>> +}
>> +
>> +void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr)
>> +{
>> + struct folio *folio = page_folio(page);
>> + struct vm_area_struct *vma = vmf->vma;
>> + bool cow = (vmf->flags & FAULT_FLAG_WRITE) &&
>> + !(vma->vm_flags & VM_SHARED);
>> +
>> + if (cow) {
>> inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
>> page_add_new_anon_rmap(page, vma, addr);
>
> As raised, we cannot PTE-map a multi-page folio that way.
>
> This function only supports single-page anon folios.
>
> page_add_new_anon_rmap() -> folio_add_new_anon_rmap(). As that documents:
>
> "If the folio is large, it is accounted as a THP" -- for example, we would only increment the "entire mapcount" and set the PageAnonExclusive bit only on the head page.
>
> So this really doesn't work for multi-page folios and if the function would be used for that, we'd be in trouble.
>
> We'd want some fence here to detect that and bail out if we'd be instructed to do that. At least a WARN_ON_ONCE() I guess.
> update_mmu_tlb(vma, vmf->address, vmf->pte);
>
> Right now the function looks like it might just handle that.
You are right. I thought moving cow case out of it can make it explicit.
But looks like it doesn't. I will add WARN_ON_ONCE(). Thanks.
Regards
Yin, Fengwei
>
