linux-kernel - Re: [PATCH 1/3] mm: add functions folio_in_range() and folio_within

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Message-Id: <20230728113412.65741d2dd23228d0e2c0cb8d@linux-foundation.org>
Date:   Fri, 28 Jul 2023 11:34:12 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Yin Fengwei <fengwei.yin@...el.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        yuzhao@...gle.com, willy@...radead.org, david@...hat.com,
        ryan.roberts@....com, shy828301@...il.com, hughd@...gle.com
Subject: Re: [PATCH 1/3] mm: add functions folio_in_range() and
 folio_within_vma()

On Fri, 28 Jul 2023 15:09:27 +0800 Yin Fengwei <fengwei.yin@...el.com> 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().
> 
> ...
>
> --- 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 looks crazily way too large to be inlined?

> +	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;
> +	}
> +
> +	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);
> +}

And this doesn't.