| 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
| ||
|
Message-ID: <9c86c4ad-2659-4091-9f2a-d166c5e8daa3@kernel.org>
Date: Fri, 14 Nov 2025 20:43:43 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org, linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
Christophe Leroy <christophe.leroy@...roup.eu>,
Sourabh Jain <sourabhjain@...ux.ibm.com>,
Andrew Morton <akpm@...ux-foundation.org>,
"Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
Madhavan Srinivasan <maddy@...ux.ibm.com>, Donet Tom
<donettom@...ux.ibm.com>, Michael Ellerman <mpe@...erman.id.au>,
Nicholas Piggin <npiggin@...il.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>,
Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH v1] mm: fix MAX_FOLIO_ORDER on powerpc configs with
hugetlb
On 12.11.25 15:56, David Hildenbrand (Red Hat) wrote:
> In the past, CONFIG_ARCH_HAS_GIGANTIC_PAGE indicated that we support
> runtime allocation of gigantic hugetlb folios. In the meantime it evolved
> into a generic way for the architecture to state that it supports
> gigantic hugetlb folios.
>
> In commit fae7d834c43c ("mm: add __dump_folio()") we started using
> CONFIG_ARCH_HAS_GIGANTIC_PAGE to decide MAX_FOLIO_ORDER: whether we could
> have folios larger than what the buddy can handle. In the context of
> that commit, we started using MAX_FOLIO_ORDER to detect page corruptions
> when dumping tail pages of folios. Before that commit, we assumed that
> we cannot have folios larger than the highest buddy order, which was
> obviously wrong.
>
> In commit 7b4f21f5e038 ("mm/hugetlb: check for unreasonable folio sizes
> when registering hstate"), we used MAX_FOLIO_ORDER to detect
> inconsistencies, and in fact, we found some now.
>
> Powerpc allows for configs that can allocate gigantic folio during boot
> (not at runtime), that do not set CONFIG_ARCH_HAS_GIGANTIC_PAGE and can
> exceed PUD_ORDER.
>
> To fix it, let's make powerpc select CONFIG_ARCH_HAS_GIGANTIC_PAGE with
> hugetlb on powerpc, and increase the maximum folio size with hugetlb to 16
> GiB (possible on arm64 and powerpc). Note that on some powerpc
> configurations, whether we actually have gigantic pages
> depends on the setting of CONFIG_ARCH_FORCE_MAX_ORDER, but there is
> nothing really problematic about setting it unconditionally: we just try to
> keep the value small so we can better detect problems in __dump_folio()
> and inconsistencies around the expected largest folio in the system.
>
> Ideally, we'd have a better way to obtain the maximum hugetlb folio size
> and detect ourselves whether we really end up with gigantic folios. Let's
> defer bigger changes and fix the warnings first.
>
> While at it, handle gigantic DAX folios more clearly: DAX can only
> end up creating gigantic folios with HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD.
>
> Add a new Kconfig option HAVE_GIGANTIC_FOLIOS to make both cases
> clearer. In particular, worry about ARCH_HAS_GIGANTIC_PAGE only with
> HUGETLB_PAGE.
>
> Note: with enabling CONFIG_ARCH_HAS_GIGANTIC_PAGE on powerpc, we will now
> also allow for runtime allocations of folios in some more powerpc configs.
> I don't think this is a problem, but if it is we could handle it through
> __HAVE_ARCH_GIGANTIC_PAGE_RUNTIME_SUPPORTED.
>
> While __dump_page()/__dump_folio was also problematic (not handling dumping
> of tail pages of such gigantic folios correctly), it doesn't relevant
> critical enough to mark it as a fix.
>
> Fixes: 7b4f21f5e038 ("mm/hugetlb: check for unreasonable folio sizes when registering hstate")
> Reported-by: Christophe Leroy <christophe.leroy@...roup.eu>
> Closes: https://lore.kernel.org/r/3e043453-3f27-48ad-b987-cc39f523060a@csgroup.eu/
> Reported-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
> Closes: https://lore.kernel.org/r/94377f5c-d4f0-4c0f-b0f6-5bf1cd7305b1@linux.ibm.com/
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Ritesh Harjani (IBM) <ritesh.list@...il.com>
> Cc: Madhavan Srinivasan <maddy@...ux.ibm.com>
> Cc: Donet Tom <donettom@...ux.ibm.com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Nicholas Piggin <npiggin@...il.com>
> Cc: Christophe Leroy <christophe.leroy@...roup.eu>
> Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Mike Rapoport <rppt@...nel.org>
> Cc: Suren Baghdasaryan <surenb@...gle.com>
> Cc: Michal Hocko <mhocko@...e.com>
> Signed-off-by: David Hildenbrand (Red Hat) <david@...nel.org>
> ---
> arch/powerpc/Kconfig | 1 +
> include/linux/mm.h | 12 +++++++++---
> mm/Kconfig | 7 +++++++
> 3 files changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index e24f4d88885ae..9537a61ebae02 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -137,6 +137,7 @@ config PPC
> select ARCH_HAS_DMA_OPS if PPC64
> select ARCH_HAS_FORTIFY_SOURCE
> select ARCH_HAS_GCOV_PROFILE_ALL
> + select ARCH_HAS_GIGANTIC_PAGE if ARCH_SUPPORTS_HUGETLBFS
> select ARCH_HAS_KCOV
> select ARCH_HAS_KERNEL_FPU_SUPPORT if PPC64 && PPC_FPU
> select ARCH_HAS_MEMBARRIER_CALLBACKS
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index d16b33bacc32b..63aea4b3fb5d9 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2074,7 +2074,7 @@ static inline unsigned long folio_nr_pages(const struct folio *folio)
> return folio_large_nr_pages(folio);
> }
>
> -#if !defined(CONFIG_ARCH_HAS_GIGANTIC_PAGE)
> +#if !defined(CONFIG_HAVE_GIGANTIC_FOLIOS)
> /*
> * We don't expect any folios that exceed buddy sizes (and consequently
> * memory sections).
> @@ -2087,10 +2087,16 @@ static inline unsigned long folio_nr_pages(const struct folio *folio)
> * pages are guaranteed to be contiguous.
> */
> #define MAX_FOLIO_ORDER PFN_SECTION_SHIFT
> -#else
> +#elif defined(CONFIG_HUGETLB_PAGE)
> /*
> * There is no real limit on the folio size. We limit them to the maximum we
> - * currently expect (e.g., hugetlb, dax).
> + * currently expect: with hugetlb, we expect no folios larger than 16 GiB.
> + */
> +#define MAX_FOLIO_ORDER get_order(SZ_16G)
Turns out that's a problem on 32bit builds, because it won't fit into unsigned long. Grml.
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 63aea4b3fb5d9..f595565bdd113 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2090,9 +2090,10 @@ static inline unsigned long folio_nr_pages(const struct folio *folio)
#elif defined(CONFIG_HUGETLB_PAGE)
/*
* There is no real limit on the folio size. We limit them to the maximum we
- * currently expect: with hugetlb, we expect no folios larger than 16 GiB.
+ * currently expect: with hugetlb, we expect no folios larger than 16 GiB
+ * on 64bit and 1 GiB on 32bit.
*/
-#define MAX_FOLIO_ORDER get_order(SZ_16G)
+#define MAX_FOLIO_ORDER get_order(IS_ENABLED(CONFIG_64BIT) ? SZ_16G : SZ_1G)
#else
/*
I'll resend the patch ...
--
Cheers
David
Powered by blists - more mailing lists