Commit 29cb8051 authored by Ryan Roberts's avatar Ryan Roberts Committed by Will Deacon
Browse files

arm64: hugetlb: Cleanup huge_pte size discovery mechanisms 



Not all huge_pte helper APIs explicitly provide the size of the
huge_pte. So the helpers have to depend on various methods to determine
the size of the huge_pte. Some of these methods are dubious.

Let's clean up the code to use preferred methods and retire the dubious
ones. The options in order of preference:

 - If size is provided as parameter, use it together with
   num_contig_ptes(). This is explicit and works for both present and
   non-present ptes.

 - If vma is provided as a parameter, retrieve size via
   huge_page_size(hstate_vma(vma)) and use it together with
   num_contig_ptes(). This is explicit and works for both present and
   non-present ptes.

 - If the pte is present and contiguous, use find_num_contig() to walk
   the pgtable to find the level and infer the number of ptes from
   level. Only works for *present* ptes.

 - If the pte is present and not contiguous and you can infer from this
   that only 1 pte needs to be operated on. This is ok if you don't care
   about the absolute size, and just want to know the number of ptes.

 - NEVER rely on resolving the PFN of a present pte to a folio and
   getting the folio's size. This is fragile at best, because there is
   nothing to stop the core-mm from allocating a folio twice as big as
   the huge_pte then mapping it across 2 consecutive huge_ptes. Or just
   partially mapping it.

Where we require that the pte is present, add warnings if not-present.

Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Reviewed-by: default avatarAnshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: default avatarRyan Roberts <ryan.roberts@arm.com>
Tested-by: default avatarLuiz Capitulino <luizcap@redhat.com>
Link: https://lore.kernel.org/r/20250422081822.1836315-2-ryan.roberts@arm.com


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent fcf8dda8

arch/arm64/mm/hugetlbpage.c

+15 −5
Original line number Diff line number Diff line
@@ -129,7 +129,7 @@ pte_t huge_ptep_get(struct mm_struct *mm, unsigned long addr, pte_t *ptep) 
	if (!pte_present(orig_pte) || !pte_cont(orig_pte))

		return orig_pte;



	ncontig = num_contig_ptes(page_size(pte_page(orig_pte)), &pgsize);

	ncontig = find_num_contig(mm, addr, ptep, &pgsize);

	for (i = 0; i < ncontig; i++, ptep++) {

		pte_t pte = __ptep_get(ptep);
@@ -438,16 +438,19 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma, 
	pgprot_t hugeprot;

	pte_t orig_pte;



	VM_WARN_ON(!pte_present(pte));



	if (!pte_cont(pte))

		return __ptep_set_access_flags(vma, addr, ptep, pte, dirty);



	ncontig = find_num_contig(mm, addr, ptep, &pgsize);

	ncontig = num_contig_ptes(huge_page_size(hstate_vma(vma)), &pgsize);

	dpfn = pgsize >> PAGE_SHIFT;



	if (!__cont_access_flags_changed(ptep, pte, ncontig))

		return 0;



	orig_pte = get_clear_contig_flush(mm, addr, ptep, pgsize, ncontig);

	VM_WARN_ON(!pte_present(orig_pte));



	/* Make sure we don't lose the dirty or young state */

	if (pte_dirty(orig_pte))
@@ -472,7 +475,10 @@ void huge_ptep_set_wrprotect(struct mm_struct *mm, 
	size_t pgsize;

	pte_t pte;



	if (!pte_cont(__ptep_get(ptep))) {

	pte = __ptep_get(ptep);

	VM_WARN_ON(!pte_present(pte));



	if (!pte_cont(pte)) {

		__ptep_set_wrprotect(mm, addr, ptep);

		return;

	}
@@ -496,11 +502,15 @@ pte_t huge_ptep_clear_flush(struct vm_area_struct *vma, 
	struct mm_struct *mm = vma->vm_mm;

	size_t pgsize;

	int ncontig;

	pte_t pte;



	pte = __ptep_get(ptep);

	VM_WARN_ON(!pte_present(pte));



	if (!pte_cont(__ptep_get(ptep)))

	if (!pte_cont(pte))

		return ptep_clear_flush(vma, addr, ptep);



	ncontig = find_num_contig(mm, addr, ptep, &pgsize);

	ncontig = num_contig_ptes(huge_page_size(hstate_vma(vma)), &pgsize);

	return get_clear_contig_flush(mm, addr, ptep, pgsize, ncontig);

}