linux-kernel - Re: [PATCH v1 2/2] mm/huge_memory: don't mark refcounted pages special in vmf_insert_folio

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <d43be0c9-cad5-4712-813b-225e9969d84e@redhat.com>
Date: Wed, 4 Jun 2025 00:02:51 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org, nvdimm@...ts.linux.dev, linux-cxl@...r.kernel.org,
 Andrew Morton <akpm@...ux-foundation.org>,
 Alistair Popple <apopple@...dia.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
 <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Zi Yan <ziy@...dia.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
 Dev Jain <dev.jain@....com>, Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v1 2/2] mm/huge_memory: don't mark refcounted pages
 special in vmf_insert_folio_pud()

On 03.06.25 23:16, David Hildenbrand wrote:
> Marking PUDs that map a "normal" refcounted folios as special is
> against our rules documented for vm_normal_page().
> 
> 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 by just inlining the relevant code, making the whole
> pud_none() handling cleaner.
> 
> Add folio_mk_pud() to mimic what we do with folio_mk_pmd().
> 
> While at it, make sure that the pud that is non-none is actually present
> before comparing PFNs.
> 
> Fixes: dbe54153296d ("mm/huge_memory: add vmf_insert_folio_pud()")
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>   include/linux/mm.h | 15 +++++++++++++++
>   mm/huge_memory.c   | 33 +++++++++++++++++++++++----------
>   2 files changed, 38 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 0ef2ba0c667af..047c8261d4002 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1816,6 +1816,21 @@ static inline pmd_t folio_mk_pmd(struct folio *folio, pgprot_t pgprot)
>   {
>   	return pmd_mkhuge(pfn_pmd(folio_pfn(folio), pgprot));
>   }
> +
> +/**
> + * 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
>   #endif /* CONFIG_MMU */

The following on top should make cross-compiles happy (git diff output because it's late
here, probably whitespace messed up):


diff --git a/include/linux/mm.h b/include/linux/mm.h
index 047c8261d4002..b7e2abd8ce0df 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1817,6 +1817,7 @@ static inline pmd_t folio_mk_pmd(struct folio *folio, pgprot_t pgprot)
         return pmd_mkhuge(pfn_pmd(folio_pfn(folio), pgprot));
  }
  
+#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
  /**
   * folio_mk_pud - Create a PUD for this folio
   * @folio: The folio to create a PUD for
@@ -1831,7 +1832,8 @@ static inline pud_t folio_mk_pud(struct folio *folio, pgprot_t pgprot)
  {
         return pud_mkhuge(pfn_pud(folio_pfn(folio), pgprot));
  }
-#endif
+#endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
  #endif /* CONFIG_MMU */
  
  static inline bool folio_has_pincount(const struct folio *folio

-- 
Cheers,

David / dhildenb