On 8/2/2023 7:35 PM, Ryan Roberts wrote: > On 02/08/2023 12:14, Ryan Roberts wrote: >> On 28/07/2023 08:09, Yin Fengwei wrote: >>> It will be used to check whether the folio is mapped to specific >>> VMA and whether the mapping address of folio is in the range. >>> >>> Also a helper function folio_within_vma() to check whether folio >>> is in the range of vma based on folio_in_range(). >>> >>> Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx> >>> --- >>> mm/internal.h | 69 +++++++++++++++++++++++++++++++++++++++++++++++++++ >>> 1 file changed, 69 insertions(+) >>> >>> diff --git a/mm/internal.h b/mm/internal.h >>> index 5a03bc4782a2..63de32154a48 100644 >>> --- a/mm/internal.h >>> +++ b/mm/internal.h >>> @@ -585,6 +585,75 @@ extern long faultin_vma_page_range(struct vm_area_struct *vma, >>> bool write, int *locked); >>> extern bool mlock_future_ok(struct mm_struct *mm, unsigned long flags, >>> unsigned long bytes); >>> + >>> +/* >>> + * Check whether the folio is in specific range >>> + * >>> + * First, check whether the folio is in the range of vma. >>> + * Then, check whether the folio is mapped to the range of [start, end]. >>> + * In the end, check whether the folio is fully mapped to the range. >>> + * >>> + * @pte page table pointer will be checked whether the large folio >>> + * is fully mapped to. Currently, if mremap in the middle of >>> + * large folio, the large folio could be mapped to to different >>> + * VMA and address check can't identify this situation. >>> + */ >>> +static inline bool >>> +folio_in_range(struct folio *folio, struct vm_area_struct *vma, >>> + unsigned long start, unsigned long end, pte_t *pte) >> >> This api seems a bit redundant to me. Wouldn't it be better to remove the vma >> parameter and instead fix up the start/end addresses in folio_within_vma()? > > I have created a function as part of my "pte batch-zap" patch set [1], which > counts the number of contiguously mapped pages of a folio > (folio_nr_pages_cont_mapped()). I wonder if actually this should be the > primitive, which can be shared for more cases. Then your folio_within_vma() > function could just compare the nr_pages to folio_nr_pages() to decide if the > folio is fully and contiguously mapped in the VMA. That means we need to unify the parameters. But I don't care about the page and you don't care about the VMA. :). Maybe we can share the PTE check part? > > I also wonder if you should change the name of folio_within_vma() to something > like folio_test_cont_in_vma() to disambiguate from the case where the folio may > be fully mapped with a discontiguity (although perhaps that's not possible > because a mremap would result in distinct vmas... would a new mmap in the hole > cause a merge of all 3?). I don't think it's possible as mremap reuse original pgoff of VMA to new VMA. I suppose it will prevent VMA merging. But I didn't check detail. I hate to add the PTE check as it makes folio_within_vma() much heavy and can only be called with page table holding. But MREMAP_DONTUNMAP could create the VMA which just has part of folio mapped. And the first version folio_within_vma() can't identify it. Regards Yin, Fengwei > > [1] https://lore.kernel.org/linux-mm/20230727141837.3386072-4-ryan.roberts@xxxxxxx/ > >> >>> +{ >>> + pte_t ptent; >>> + unsigned long i, nr = folio_nr_pages(folio); >>> + pgoff_t pgoff, addr; >>> + unsigned long vma_pglen = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT; >>> + >>> + VM_WARN_ON_FOLIO(folio_test_ksm(folio), folio); >>> + >>> + if (start < vma->vm_start) >>> + start = vma->vm_start; >>> + if (end > vma->vm_end) >>> + end = vma->vm_end; >>> + >>> + pgoff = folio_pgoff(folio); >>> + /* if folio start address is not in vma range */ >>> + if (pgoff < vma->vm_pgoff || pgoff > vma->vm_pgoff + vma_pglen) >>> + return false; >>> + >>> + addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT); >>> + if (addr < start || end - addr < folio_size(folio)) >>> + return false; >>> + >>> + /* not necessary to check pte for none large folio */ >>> + if (!folio_test_large(folio)) >>> + return true; >>> + >>> + if (!pte) >>> + return false; >>> + >>> + /* check whether parameter pte is associated with folio */ >>> + ptent = ptep_get(pte); >>> + if (pte_none(ptent) || !pte_present(ptent) || >>> + pte_pfn(ptent) - folio_pfn(folio) >= nr) >>> + return false; >>> + >>> + pte -= pte_pfn(ptent) - folio_pfn(folio); >>> + for (i = 0; i < nr; i++, pte++) { >>> + ptent = ptep_get(pte); >>> + >>> + if (pte_none(ptent) || !pte_present(ptent) || >>> + pte_pfn(ptent) - folio_pfn(folio) >= nr) >>> + return false; >>> + } >> >> I don't think I see anything to ensure you don't wander off the end (or start) >> of the pgtable? If the folio is mremapped so that it straddles multiple tables >> (or is bigger than a single table?) then I think pte can become invalid? Perhaps >> you intended start/end to always be within the same pgtable, but that is not >> guarranteed in the case that folio_within_vma() is making the call. >> >> Also I want to check that this function is definitely always called under the >> PTL for the table that pte belongs to? >> >>> + >>> + return true; >>> +} >>> + >>> +static inline bool >>> +folio_within_vma(struct folio *folio, struct vm_area_struct *vma, pte_t *pte) >>> +{ >>> + return folio_in_range(folio, vma, vma->vm_start, vma->vm_end, pte); >>> +} >>> + >>> /* >>> * mlock_vma_folio() and munlock_vma_folio(): >>> * should be called with vma's mmap_lock held for read or write, >> >
