Re: [PATCH 1/3] mm: add functions folio_in_range() and folio_within_vma()

Yin, Fengwei
2023-08-02T12:52:45Z

On 8/2/2023 7:14 PM, 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@intel.com>
>> ---
>> 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()?
My understanding is it's necessary. As for madvise, we need to check whether
the folio is both in the range of VMA and also in the range of [start, end).

>
>> +{
>> + 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.
If pte is invalid for any reason (pass wrong parameter, not fully mapped etc), this
function just return false in page table entry check phase.

>
> Also I want to check that this function is definitely always called under the
> PTL for the table that pte belongs to?
Yes. I should spell it out. Thanks.

Regards
Yin, Fengwei

>
>> +
>> + 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,
>