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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 3DE981C000B X-Rspam-User: X-Stat-Signature: hwzxrxtggftjkn4c8x1a1k5gum87nocg X-Rspamd-Server: rspam03 X-HE-Tag: 1700735200-553970 X-HE-Meta: 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 XUZ6hvqU nYJoDxAZ2ZvnyzrdV9B8DMaIekJcHQZ927azeGU4YJvp2duO28eQfSXCTeddQnBwIvh+QfueRXLTgl+c7vgxvpOKA1E95kqa1PSYHropGeFRgeA8KW9c6rZRszTB275I75yFLjHOGNRgT26FGZaih3bnbE++ivtcrwd4O5KHyHBl9K8JJbAlTLUnIQ5yORbW+uX6cmnl/dH0rEmmZB7bTFbyEQLrTdlSRMUbcWMf2ciM5wLk4Rse2M9t7ui9aJKFBNJFyhjvuKkcFJLJ77cpopSy39g== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 16/11/2023 14:15, David Hildenbrand wrote: > On 16.11.23 15:13, David Hildenbrand wrote: >> On 16.11.23 14:49, Ryan Roberts wrote: >>> On 16/11/2023 13:20, David Hildenbrand wrote: >>>> On 16.11.23 12:20, Ryan Roberts wrote: >>>>> On 16/11/2023 11:03, David Hildenbrand wrote: >>>>>> On 15.11.23 17:30, Ryan Roberts wrote: >>>>>>> Convert copy_pte_range() to copy a set of ptes in a batch. A given batch >>>>>>> maps a physically contiguous block of memory, all belonging to the same >>>>>>> folio, with the same permissions, and for shared mappings, the same >>>>>>> dirty state. This will likely improve performance by a tiny amount due >>>>>>> to batching the folio reference count management and calling set_ptes() >>>>>>> rather than making individual calls to set_pte_at(). >>>>>>> >>>>>>> However, the primary motivation for this change is to reduce the number >>>>>>> of tlb maintenance operations that the arm64 backend has to perform >>>>>>> during fork, as it is about to add transparent support for the >>>>>>> "contiguous bit" in its ptes. By write-protecting the parent using the >>>>>>> new ptep_set_wrprotects() (note the 's' at the end) function, the >>>>>>> backend can avoid having to unfold contig ranges of PTEs, which is >>>>>>> expensive, when all ptes in the range are being write-protected. >>>>>>> Similarly, by using set_ptes() rather than set_pte_at() to set up ptes >>>>>>> in the child, the backend does not need to fold a contiguous range once >>>>>>> they are all populated - they can be initially populated as a contiguous >>>>>>> range in the first place. >>>>>>> >>>>>>> This change addresses the core-mm refactoring only, and introduces >>>>>>> ptep_set_wrprotects() with a default implementation that calls >>>>>>> ptep_set_wrprotect() for each pte in the range. A separate change will >>>>>>> implement ptep_set_wrprotects() in the arm64 backend to realize the >>>>>>> performance improvement as part of the work to enable contpte mappings. >>>>>>> >>>>>>> Signed-off-by: Ryan Roberts >>>>>>> --- >>>>>>>      include/linux/pgtable.h |  13 +++ >>>>>>>      mm/memory.c             | 175 +++++++++++++++++++++++++++++++--------- >>>>>>>      2 files changed, 150 insertions(+), 38 deletions(-) >>>>>>> >>>>>>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h >>>>>>> index af7639c3b0a3..1c50f8a0fdde 100644 >>>>>>> --- a/include/linux/pgtable.h >>>>>>> +++ b/include/linux/pgtable.h >>>>>>> @@ -622,6 +622,19 @@ static inline void ptep_set_wrprotect(struct mm_struct >>>>>>> *mm, unsigned long addres >>>>>>>      } >>>>>>>      #endif >>>>>>>      +#ifndef ptep_set_wrprotects >>>>>>> +struct mm_struct; >>>>>>> +static inline void ptep_set_wrprotects(struct mm_struct *mm, >>>>>>> +                unsigned long address, pte_t *ptep, >>>>>>> +                unsigned int nr) >>>>>>> +{ >>>>>>> +    unsigned int i; >>>>>>> + >>>>>>> +    for (i = 0; i < nr; i++, address += PAGE_SIZE, ptep++) >>>>>>> +        ptep_set_wrprotect(mm, address, ptep); >>>>>>> +} >>>>>>> +#endif >>>>>>> + >>>>>>>      /* >>>>>>>       * On some architectures hardware does not set page access bit when >>>>>>> accessing >>>>>>>       * memory page, it is responsibility of software setting this bit. >>>>>>> It brings >>>>>>> diff --git a/mm/memory.c b/mm/memory.c >>>>>>> index 1f18ed4a5497..b7c8228883cf 100644 >>>>>>> --- a/mm/memory.c >>>>>>> +++ b/mm/memory.c >>>>>>> @@ -921,46 +921,129 @@ copy_present_page(struct vm_area_struct *dst_vma, >>>>>>> struct vm_area_struct *src_vma >>>>>>>              /* Uffd-wp needs to be delivered to dest pte as well */ >>>>>>>              pte = pte_mkuffd_wp(pte); >>>>>>>          set_pte_at(dst_vma->vm_mm, addr, dst_pte, pte); >>>>>>> -    return 0; >>>>>>> +    return 1; >>>>>>> +} >>>>>>> + >>>>>>> +static inline unsigned long page_cont_mapped_vaddr(struct page *page, >>>>>>> +                struct page *anchor, unsigned long anchor_vaddr) >>>>>>> +{ >>>>>>> +    unsigned long offset; >>>>>>> +    unsigned long vaddr; >>>>>>> + >>>>>>> +    offset = (page_to_pfn(page) - page_to_pfn(anchor)) << PAGE_SHIFT; >>>>>>> +    vaddr = anchor_vaddr + offset; >>>>>>> + >>>>>>> +    if (anchor > page) { >>>>>>> +        if (vaddr > anchor_vaddr) >>>>>>> +            return 0; >>>>>>> +    } else { >>>>>>> +        if (vaddr < anchor_vaddr) >>>>>>> +            return ULONG_MAX; >>>>>>> +    } >>>>>>> + >>>>>>> +    return vaddr; >>>>>>> +} >>>>>>> + >>>>>>> +static int folio_nr_pages_cont_mapped(struct folio *folio, >>>>>>> +                      struct page *page, pte_t *pte, >>>>>>> +                      unsigned long addr, unsigned long end, >>>>>>> +                      pte_t ptent, bool *any_dirty) >>>>>>> +{ >>>>>>> +    int floops; >>>>>>> +    int i; >>>>>>> +    unsigned long pfn; >>>>>>> +    pgprot_t prot; >>>>>>> +    struct page *folio_end; >>>>>>> + >>>>>>> +    if (!folio_test_large(folio)) >>>>>>> +        return 1; >>>>>>> + >>>>>>> +    folio_end = &folio->page + folio_nr_pages(folio); >>>>>>> +    end = min(page_cont_mapped_vaddr(folio_end, page, addr), end); >>>>>>> +    floops = (end - addr) >> PAGE_SHIFT; >>>>>>> +    pfn = page_to_pfn(page); >>>>>>> +    prot = pte_pgprot(pte_mkold(pte_mkclean(ptent))); >>>>>>> + >>>>>>> +    *any_dirty = pte_dirty(ptent); >>>>>>> + >>>>>>> +    pfn++; >>>>>>> +    pte++; >>>>>>> + >>>>>>> +    for (i = 1; i < floops; i++) { >>>>>>> +        ptent = ptep_get(pte); >>>>>>> +        ptent = pte_mkold(pte_mkclean(ptent)); >>>>>>> + >>>>>>> +        if (!pte_present(ptent) || pte_pfn(ptent) != pfn || >>>>>>> +            pgprot_val(pte_pgprot(ptent)) != pgprot_val(prot)) >>>>>>> +            break; >>>>>>> + >>>>>>> +        if (pte_dirty(ptent)) >>>>>>> +            *any_dirty = true; >>>>>>> + >>>>>>> +        pfn++; >>>>>>> +        pte++; >>>>>>> +    } >>>>>>> + >>>>>>> +    return i; >>>>>>>      } >>>>>>>        /* >>>>>>> - * Copy one pte.  Returns 0 if succeeded, or -EAGAIN if one preallocated >>>>>>> page >>>>>>> - * is required to copy this pte. >>>>>>> + * Copy set of contiguous ptes.  Returns number of ptes copied if succeeded >>>>>>> + * (always gte 1), or -EAGAIN if one preallocated page is required to >>>>>>> copy the >>>>>>> + * first pte. >>>>>>>       */ >>>>>>>      static inline int >>>>>>> -copy_present_pte(struct vm_area_struct *dst_vma, struct vm_area_struct >>>>>>> *src_vma, >>>>>>> -         pte_t *dst_pte, pte_t *src_pte, unsigned long addr, int *rss, >>>>>>> -         struct folio **prealloc) >>>>>>> +copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct >>>>>>> *src_vma, >>>>>>> +          pte_t *dst_pte, pte_t *src_pte, >>>>>>> +          unsigned long addr, unsigned long end, >>>>>>> +          int *rss, struct folio **prealloc) >>>>>>>      { >>>>>>>          struct mm_struct *src_mm = src_vma->vm_mm; >>>>>>>          unsigned long vm_flags = src_vma->vm_flags; >>>>>>>          pte_t pte = ptep_get(src_pte); >>>>>>>          struct page *page; >>>>>>>          struct folio *folio; >>>>>>> +    int nr = 1; >>>>>>> +    bool anon; >>>>>>> +    bool any_dirty = pte_dirty(pte); >>>>>>> +    int i; >>>>>>>            page = vm_normal_page(src_vma, addr, pte); >>>>>>> -    if (page) >>>>>>> +    if (page) { >>>>>>>              folio = page_folio(page); >>>>>>> -    if (page && folio_test_anon(folio)) { >>>>>>> -        /* >>>>>>> -         * If this page may have been pinned by the parent process, >>>>>>> -         * copy the page immediately for the child so that we'll always >>>>>>> -         * guarantee the pinned page won't be randomly replaced in the >>>>>>> -         * future. >>>>>>> -         */ >>>>>>> -        folio_get(folio); >>>>>>> -        if (unlikely(page_try_dup_anon_rmap(page, false, src_vma))) { >>>>>>> -            /* Page may be pinned, we have to copy. */ >>>>>>> -            folio_put(folio); >>>>>>> -            return copy_present_page(dst_vma, src_vma, dst_pte, src_pte, >>>>>>> -                         addr, rss, prealloc, page); >>>>>>> +        anon = folio_test_anon(folio); >>>>>>> +        nr = folio_nr_pages_cont_mapped(folio, page, src_pte, addr, >>>>>>> +                        end, pte, &any_dirty); >>>>>>> + >>>>>>> +        for (i = 0; i < nr; i++, page++) { >>>>>>> +            if (anon) { >>>>>>> +                /* >>>>>>> +                 * If this page may have been pinned by the >>>>>>> +                 * parent process, copy the page immediately for >>>>>>> +                 * the child so that we'll always guarantee the >>>>>>> +                 * pinned page won't be randomly replaced in the >>>>>>> +                 * future. >>>>>>> +                 */ >>>>>>> +                if (unlikely(page_try_dup_anon_rmap( >>>>>>> +                        page, false, src_vma))) { >>>>>>> +                    if (i != 0) >>>>>>> +                        break; >>>>>>> +                    /* Page may be pinned, we have to copy. */ >>>>>>> +                    return copy_present_page( >>>>>>> +                        dst_vma, src_vma, dst_pte, >>>>>>> +                        src_pte, addr, rss, prealloc, >>>>>>> +                        page); >>>>>>> +                } >>>>>>> +                rss[MM_ANONPAGES]++; >>>>>>> +                VM_BUG_ON(PageAnonExclusive(page)); >>>>>>> +            } else { >>>>>>> +                page_dup_file_rmap(page, false); >>>>>>> +                rss[mm_counter_file(page)]++; >>>>>>> +            } >>>>>>>              } >>>>>>> -        rss[MM_ANONPAGES]++; >>>>>>> -    } else if (page) { >>>>>>> -        folio_get(folio); >>>>>>> -        page_dup_file_rmap(page, false); >>>>>>> -        rss[mm_counter_file(page)]++; >>>>>>> + >>>>>>> +        nr = i; >>>>>>> +        folio_ref_add(folio, nr); >>>>>>>          } >>>>>>>            /* >>>>>>> @@ -968,24 +1051,28 @@ copy_present_pte(struct vm_area_struct *dst_vma, >>>>>>> struct >>>>>>> vm_area_struct *src_vma, >>>>>>>           * in the parent and the child >>>>>>>           */ >>>>>>>          if (is_cow_mapping(vm_flags) && pte_write(pte)) { >>>>>>> -        ptep_set_wrprotect(src_mm, addr, src_pte); >>>>>>> +        ptep_set_wrprotects(src_mm, addr, src_pte, nr); >>>>>>>              pte = pte_wrprotect(pte); >>>>>> >>>>>> You likely want an "any_pte_writable" check here instead, no? >>>>>> >>>>>> Any operations that target a single indiividual PTE while multiple PTEs are >>>>>> adjusted are suspicious :) >>>>> >>>>> The idea is that I've already constrained the batch of pages such that the >>>>> permissions are all the same (see folio_nr_pages_cont_mapped()). So if the >>>>> first >>>>> pte is writable, then they all are - something has gone badly wrong if some >>>>> are >>>>> writable and others are not. >>>> >>>> I wonder if it would be cleaner and easier to not do that, though. >>>> >>>> Simply record if any pte is writable. Afterwards they will *all* be R/O and you >>>> can set the cont bit, correct? >>> >>> Oh I see what you mean - that only works for cow mappings though. If you have a >>> shared mapping, you won't be making it read-only at fork. So if we ignore >>> pte_write() state when demarking the batches, we will end up with a batch of >>> pages with a mix of RO and RW in the parent, but then we set_ptes() for the >>> child and those pages will all have the permissions of the first page of the >>> batch. >> >> I see what you mean. >> >> After fork(), all anon pages will be R/O in the parent and the child. >> Easy. If any PTE is writable, wrprotect all in the parent and the child. >> >> After fork(), all shared pages can be R/O or R/W in the parent. For >> simplicity, I think you can simply set them all R/O in the child. So if >> any PTE is writable, wrprotect all in the child. > > Or better: if any is R/O, set them all R/O. Otherwise just leave them as is. I've just come back to this to code it up, and want to clarify this last comment; I'm already going to have to collect any_writable for the anon case, so I will already have that info for the shared case too. I think you are suggesting I *additionally* collect any_readonly, then in the shared case, I only apply wrprotect if (any_writable && any_readonly). i.e. only apply wrprotect if there is a mix of permissions for the batch, otherwise all the permissions are the same (either all RW or all RO) and I can elide the wrprotet. Is that what you meant? > > But devil is in the detail. >