Commit 02825c09 authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
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mm/huge_memory: don't mark refcounted folios special in vmf_insert_folio_pud() 

Marking PUDs that map a "normal" refcounted folios as special is against
our rules documented for vm_normal_page().  normal (refcounted) folios
shall never have the page table mapping marked as special.

Fortunately, there are not that many pud_special() check that can be
mislead and are right now rather harmless: e.g., none so far bases
decisions whether to grab a folio reference on that decision.

Well, and GUP-fast will fallback to GUP-slow.  All in all, so far no big
implications as it seems.

Getting this right will get more important as we introduce
folio_normal_page_pud() and start using it in more place where we
currently special-case based on other VMA flags.

Fix it just like we fixed vmf_insert_folio_pmd().

Add folio_mk_pud() to mimic what we do with folio_mk_pmd().

Link: https://lkml.kernel.org/r/20250613092702.1943533-4-david@redhat.com


Fixes: dbe54153 ("mm/huge_memory: add vmf_insert_folio_pud()")
Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarDan Williams <dan.j.williams@intel.com>
Reviewed-by: default avatarLorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: default avatarJason Gunthorpe <jgg@nvidia.com>
Tested-by: default avatarDan Williams <dan.j.williams@intel.com>
Reviewed-by: default avatarOscar Salvador <osalvador@suse.de>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent c4297465

include/linux/mm.h

+18 −1
Original line number Diff line number Diff line
@@ -1816,7 +1816,24 @@ static inline pmd_t folio_mk_pmd(struct folio *folio, pgprot_t pgprot) 
{

	return pmd_mkhuge(pfn_pmd(folio_pfn(folio), pgprot));

}

#endif



#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD

/**

 * folio_mk_pud - Create a PUD for this folio

 * @folio: The folio to create a PUD for

 * @pgprot: The page protection bits to use

 *

 * Create a page table entry for the first page of this folio.

 * This is suitable for passing to set_pud_at().

 *

 * Return: A page table entry suitable for mapping this folio.

 */

static inline pud_t folio_mk_pud(struct folio *folio, pgprot_t pgprot)

{

	return pud_mkhuge(pfn_pud(folio_pfn(folio), pgprot));

}

#endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */

#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

#endif /* CONFIG_MMU */



static inline bool folio_has_pincount(const struct folio *folio)

mm/huge_memory.c

+29 −23
Original line number Diff line number Diff line
@@ -1536,15 +1536,18 @@ static pud_t maybe_pud_mkwrite(pud_t pud, struct vm_area_struct *vma) 
	return pud;

}



static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,

		pud_t *pud, pfn_t pfn, pgprot_t prot, bool write)

static void insert_pud(struct vm_area_struct *vma, unsigned long addr,

		pud_t *pud, struct folio_or_pfn fop, pgprot_t prot, bool write)

{

	struct mm_struct *mm = vma->vm_mm;

	pud_t entry;



	if (!pud_none(*pud)) {

		const unsigned long pfn = fop.is_folio ? folio_pfn(fop.folio) :

					  pfn_t_to_pfn(fop.pfn);



		if (write) {

			if (WARN_ON_ONCE(pud_pfn(*pud) != pfn_t_to_pfn(pfn)))

			if (WARN_ON_ONCE(pud_pfn(*pud) != pfn))

				return;

			entry = pud_mkyoung(*pud);

			entry = maybe_pud_mkwrite(pud_mkdirty(entry), vma);
@@ -1554,11 +1557,20 @@ static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr, 
		return;

	}



	entry = pud_mkhuge(pfn_t_pud(pfn, prot));

	if (pfn_t_devmap(pfn))

	if (fop.is_folio) {

		entry = folio_mk_pud(fop.folio, vma->vm_page_prot);



		folio_get(fop.folio);

		folio_add_file_rmap_pud(fop.folio, &fop.folio->page, vma);

		add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PUD_NR);

	} else {

		entry = pud_mkhuge(pfn_t_pud(fop.pfn, prot));



		if (pfn_t_devmap(fop.pfn))

			entry = pud_mkdevmap(entry);

		else

			entry = pud_mkspecial(entry);

	}

	if (write) {

		entry = pud_mkyoung(pud_mkdirty(entry));

		entry = maybe_pud_mkwrite(entry, vma);
@@ -1582,6 +1594,9 @@ vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write) 
	unsigned long addr = vmf->address & PUD_MASK;

	struct vm_area_struct *vma = vmf->vma;

	pgprot_t pgprot = vma->vm_page_prot;

	struct folio_or_pfn fop = {

		.pfn = pfn,

	};

	spinlock_t *ptl;



	/*
@@ -1601,7 +1616,7 @@ vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write) 
	pfnmap_setup_cachemode_pfn(pfn_t_to_pfn(pfn), &pgprot);



	ptl = pud_lock(vma->vm_mm, vmf->pud);

	insert_pfn_pud(vma, addr, vmf->pud, pfn, pgprot, write);

	insert_pud(vma, addr, vmf->pud, fop, pgprot, write);

	spin_unlock(ptl);



	return VM_FAULT_NOPAGE;
@@ -1623,6 +1638,10 @@ vm_fault_t vmf_insert_folio_pud(struct vm_fault *vmf, struct folio *folio, 
	unsigned long addr = vmf->address & PUD_MASK;

	pud_t *pud = vmf->pud;

	struct mm_struct *mm = vma->vm_mm;

	struct folio_or_pfn fop = {

		.folio = folio,

		.is_folio = true,

	};

	spinlock_t *ptl;



	if (addr < vma->vm_start || addr >= vma->vm_end)
@@ -1632,20 +1651,7 @@ vm_fault_t vmf_insert_folio_pud(struct vm_fault *vmf, struct folio *folio, 
		return VM_FAULT_SIGBUS;



	ptl = pud_lock(mm, pud);



	/*

	 * If there is already an entry present we assume the folio is

	 * already mapped, hence no need to take another reference. We

	 * still call insert_pfn_pud() though in case the mapping needs

	 * upgrading to writeable.

	 */

	if (pud_none(*vmf->pud)) {

		folio_get(folio);

		folio_add_file_rmap_pud(folio, &folio->page, vma);

		add_mm_counter(mm, mm_counter_file(folio), HPAGE_PUD_NR);

	}

	insert_pfn_pud(vma, addr, vmf->pud, pfn_to_pfn_t(folio_pfn(folio)),

		       vma->vm_page_prot, write);

	insert_pud(vma, addr, vmf->pud, fop, vma->vm_page_prot, write);

	spin_unlock(ptl);



	return VM_FAULT_NOPAGE;