[PATCH v2 0/4] mm: hugetlb: fix CMA-related issues

[PATCH v2 0/4] mm: hugetlb: fix CMA-related issues

[Qi Zheng]

From: Qi Zheng <zhengqi.arch@bytedance.com>

Hi all,

This series fixes four CMA-related issues in HugeTLB reservation,
long-term pinning and allocation:

 - Avoid ineffective CMA reservations on 32-bit x86 kernels running on
   CPUs that advertise 1 GiB page support.
 - Allow long-term pins of explicitly CMA-allocated HugeTLB folios,
   which already own their CMA bitmap ranges.
 - Preserve the caller's GFP mask when allocating from CMA.
 - Enforce cpuset restrictions on gigantic surplus allocations while
   preserving memory policy semantics.

Changes in v2:
 - Replace the PF_MEMALLOC_PIN allocation restriction with a GUP exception
   for HugeTLB folios marked HPG_cma. (suggested by Muchun Song)
 - Pass the caller's GFP mask through cma_alloc_frozen_compound() instead
   of skipping CMA when direct reclaim is disallowed.
   (suggested by sashiko)
 - Remove unnecessary revalidation of successfully allocated folios after
   cpuset changes. Retry only failed allocations.
   (pointed by Jose A. Perez de Azpillaga)
 - collect Reviewed-by and Acked-by.
 - Rebase onto next-20261104.

Qi Zheng (4):
  x86: hugetlb: disable default CMA reservations on 32-bit kernel
  mm: gup: allow long-term pins of CMA-allocated HugeTLB folios
  mm: hugetlb: fix GFP mask propagation to CMA
  mm: hugetlb: fix cpuset violations in gigantic surplus allocations

 arch/x86/mm/hugetlbpage.c |  2 +-
 include/linux/cma.h       |  2 +-
 include/linux/mm.h        | 29 +----------------------------
 mm/cma.c                  |  4 ++--
 mm/gup.c                  | 31 +++++++++++++++++++++++++++++++
 mm/hugetlb.c              | 25 ++++++++++++++++++-------
 mm/hugetlb_cma.c          |  4 ++--
 7 files changed, 56 insertions(+), 41 deletions(-)


base-commit: 8b7179210b22f8e48a82c5ceacb9d56a9c4cfec4
-- 
2.54.0

[PATCH v2 1/4] x86: hugetlb: disable default CMA reservations on 32-bit kernel

[Qi Zheng]

From: Qi Zheng <zhengqi.arch@bytedance.com>

A 32-bit x86 kernel can run on a 64-bit-capable CPU advertising GBPAGES.
arch_hugetlb_cma_order() checks only this feature and returns a nonzero
order, although gigantic HugeTLB support on x86 requires CONFIG_X86_64.
Specifying hugetlb_cma= can therefore reserve a CMA area that cannot
serve the intended gigantic HugeTLB allocations.

On non-PAE kernels, the folded PUD_SHIFT yields a 4 MiB order, which is
equal to MAX_PAGE_ORDER. With CONFIG_DEBUG_VM enabled, this triggers the
VM_WARN_ON(order <= MAX_PAGE_ORDER) check in hugetlb_cma_reserve(),
warning that hugetlb_cma is attempting to reserve a non-gigantic order.

Require CONFIG_X86_64 as well as GBPAGES when selecting the default CMA
order to avoid these ineffective reservations.

Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic hugepages using cma")
Cc: stable@vger.kernel.org
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: Muchun Song <muchun.song@linux.dev>
Reviewed-by: Jose A. Perez de Azpillaga <azpijr@gmail.com>
---
 arch/x86/mm/hugetlbpage.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
index 3b26621c91286..70726a99ede7b 100644
--- a/arch/x86/mm/hugetlbpage.c
+++ b/arch/x86/mm/hugetlbpage.c
@@ -45,7 +45,7 @@ arch_initcall(gigantic_pages_init);
 
 unsigned int __init arch_hugetlb_cma_order(void)
 {
-	if (boot_cpu_has(X86_FEATURE_GBPAGES))
+	if (IS_ENABLED(CONFIG_X86_64) && boot_cpu_has(X86_FEATURE_GBPAGES))
 		return PUD_SHIFT - PAGE_SHIFT;
 
 	return 0;
-- 
2.54.0

Re: [PATCH v2 1/4] x86: hugetlb: disable default CMA reservations on 32-bit kernel

[Oscar Salvador (SUSE)]

On Thu, Nov 05, 2026 at 12:07:43PM +0800, Qi Zheng wrote:
> From: Qi Zheng <zhengqi.arch@bytedance.com>
> 
> A 32-bit x86 kernel can run on a 64-bit-capable CPU advertising GBPAGES.
> arch_hugetlb_cma_order() checks only this feature and returns a nonzero
> order, although gigantic HugeTLB support on x86 requires CONFIG_X86_64.
> Specifying hugetlb_cma= can therefore reserve a CMA area that cannot
> serve the intended gigantic HugeTLB allocations.
> 
> On non-PAE kernels, the folded PUD_SHIFT yields a 4 MiB order, which is
> equal to MAX_PAGE_ORDER. With CONFIG_DEBUG_VM enabled, this triggers the
> VM_WARN_ON(order <= MAX_PAGE_ORDER) check in hugetlb_cma_reserve(),
> warning that hugetlb_cma is attempting to reserve a non-gigantic order.
> 
> Require CONFIG_X86_64 as well as GBPAGES when selecting the default CMA
> order to avoid these ineffective reservations.
> 
> Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic hugepages using cma")
> Cc: stable@vger.kernel.org
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> Acked-by: Muchun Song <muchun.song@linux.dev>
> Reviewed-by: Jose A. Perez de Azpillaga <azpijr@gmail.com>

Acked-by: Oscar Salvador <osalvador@suse.de>

> ---
>  arch/x86/mm/hugetlbpage.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
> index 3b26621c91286..70726a99ede7b 100644
> --- a/arch/x86/mm/hugetlbpage.c
> +++ b/arch/x86/mm/hugetlbpage.c
> @@ -45,7 +45,7 @@ arch_initcall(gigantic_pages_init);
>  
>  unsigned int __init arch_hugetlb_cma_order(void)
>  {
> -	if (boot_cpu_has(X86_FEATURE_GBPAGES))
> +	if (IS_ENABLED(CONFIG_X86_64) && boot_cpu_has(X86_FEATURE_GBPAGES))
>  		return PUD_SHIFT - PAGE_SHIFT;
>  
>  	return 0;
> -- 
> 2.54.0
> 

-- 
Oscar Salvador
SUSE Labs

[PATCH v2 2/4] mm: gup: allow long-term pins of CMA-allocated HugeTLB folios

[Qi Zheng]

From: Qi Zheng <zhengqi.arch@bytedance.com>

Long-term pinning treats explicitly CMA-allocated HugeTLB folios as
unpinnable, causing unnecessary migration or pinning failures.

These folios already own their CMA bitmap ranges, and memory blocks
overlapping CMA areas cannot be offlined. Allow HugeTLB folios with
HPG_cma to be pinned directly, including in ZONE_MOVABLE.

Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic hugepages using cma")
Cc: stable@vger.kernel.org
Suggested-by: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 include/linux/mm.h | 29 +----------------------------
 mm/gup.c           | 31 +++++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+), 28 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 2d0b8a4c9974f..75dd40265d3f4 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2975,35 +2975,8 @@ static inline bool is_zero_folio(const struct folio *folio)
 	return is_zero_page(&folio->page);
 }
 
-/* MIGRATE_CMA and ZONE_MOVABLE do not allow pin folios */
 #ifdef CONFIG_MIGRATION
-static inline bool folio_is_longterm_pinnable(struct folio *folio)
-{
-#ifdef CONFIG_CMA
-	int mt = folio_migratetype(folio);
-
-	if (mt == MIGRATE_CMA || mt == MIGRATE_ISOLATE)
-		return false;
-#endif
-	/* The zero page can be "pinned" but gets special handling. */
-	if (is_zero_folio(folio))
-		return true;
-
-	/* Coherent device memory must always allow eviction. */
-	if (folio_is_device_coherent(folio))
-		return false;
-
-	/*
-	 * Filesystems can only tolerate transient delays to truncate and
-	 * hole-punch operations
-	 */
-	if (folio_is_fsdax(folio))
-		return false;
-
-	/* Otherwise, non-movable zone folios can be pinned. */
-	return !folio_is_zone_movable(folio);
-
-}
+bool folio_is_longterm_pinnable(struct folio *folio);
 #else
 static inline bool folio_is_longterm_pinnable(struct folio *folio)
 {
diff --git a/mm/gup.c b/mm/gup.c
index 2b405cce2ca5c..e8503141bb275 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2216,6 +2216,37 @@ struct page *get_dump_page(unsigned long addr, int *locked)
 
 #ifdef CONFIG_MIGRATION
 
+bool folio_is_longterm_pinnable(struct folio *folio)
+{
+#ifdef CONFIG_CMA
+	int mt = folio_migratetype(folio);
+
+	/* Explicit HugeTLB CMA allocations own their bitmap ranges. */
+	if (folio_test_hugetlb(folio) && folio_test_hugetlb_cma(folio))
+		return true;
+
+	if (mt == MIGRATE_CMA || mt == MIGRATE_ISOLATE)
+		return false;
+#endif
+	/* The zero page can be "pinned" but gets special handling. */
+	if (is_zero_folio(folio))
+		return true;
+
+	/* Coherent device memory must always allow eviction. */
+	if (folio_is_device_coherent(folio))
+		return false;
+
+	/*
+	 * Filesystems can only tolerate transient delays to truncate and
+	 * hole-punch operations
+	 */
+	if (folio_is_fsdax(folio))
+		return false;
+
+	/* Otherwise, non-movable zone folios can be pinned. */
+	return !folio_is_zone_movable(folio);
+}
+
 /*
  * An array of either pages or folios ("pofs"). Although it may seem tempting to
  * avoid this complication, by simply interpreting a list of folios as a list of
-- 
2.54.0

Re: [PATCH v2 2/4] mm: gup: allow long-term pins of CMA-allocated HugeTLB folios

[Muchun Song]

> On Nov 5, 2026, at 12:07, Qi Zheng <qi.zheng@linux.dev> wrote:
> 
> From: Qi Zheng <zhengqi.arch@bytedance.com>
> 
> Long-term pinning treats explicitly CMA-allocated HugeTLB folios as
> unpinnable, causing unnecessary migration or pinning failures.
> 
> These folios already own their CMA bitmap ranges, and memory blocks
> overlapping CMA areas cannot be offlined. Allow HugeTLB folios with
> HPG_cma to be pinned directly, including in ZONE_MOVABLE.
> 
> Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic hugepages using cma")
> Cc: stable@vger.kernel.org
> Suggested-by: Muchun Song <muchun.song@linux.dev>
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Acked-by: Muchun Song <muchun.song@linux.dev>

But a nit bellow.

> ---
> include/linux/mm.h | 29 +----------------------------
> mm/gup.c           | 31 +++++++++++++++++++++++++++++++
> 2 files changed, 32 insertions(+), 28 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 2d0b8a4c9974f..75dd40265d3f4 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2975,35 +2975,8 @@ static inline bool is_zero_folio(const struct folio *folio)
> 	return is_zero_page(&folio->page);
> }
> 
> -/* MIGRATE_CMA and ZONE_MOVABLE do not allow pin folios */
> #ifdef CONFIG_MIGRATION
> -static inline bool folio_is_longterm_pinnable(struct folio *folio)
> -{
> -#ifdef CONFIG_CMA
> -	int mt = folio_migratetype(folio);
> -
> -	if (mt == MIGRATE_CMA || mt == MIGRATE_ISOLATE)
> -		return false;
> -#endif
> -	/* The zero page can be "pinned" but gets special handling. */
> -	if (is_zero_folio(folio))
> -		return true;
> -
> -	/* Coherent device memory must always allow eviction. */
> -	if (folio_is_device_coherent(folio))
> -		return false;
> -
> -	/*
> -	 * Filesystems can only tolerate transient delays to truncate and
> -	 * hole-punch operations
> -	 */
> -	if (folio_is_fsdax(folio))
> -		return false;
> -
> -	/* Otherwise, non-movable zone folios can be pinned. */
> -	return !folio_is_zone_movable(folio);
> -
> -}
> +bool folio_is_longterm_pinnable(struct folio *folio);
> #else
> static inline bool folio_is_longterm_pinnable(struct folio *folio)
> {
> diff --git a/mm/gup.c b/mm/gup.c
> index 2b405cce2ca5c..e8503141bb275 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2216,6 +2216,37 @@ struct page *get_dump_page(unsigned long addr, int *locked)
> 
> #ifdef CONFIG_MIGRATION
> 
> +bool folio_is_longterm_pinnable(struct folio *folio)
> +{
> +#ifdef CONFIG_CMA
> +	int mt = folio_migratetype(folio);
> +
> +	/* Explicit HugeTLB CMA allocations own their bitmap ranges. */

The description of "bitmap ranges" is weird, making me think what's the meaning of
bitmap. Please use more generic description here.

> +	if (folio_test_hugetlb(folio) && folio_test_hugetlb_cma(folio))
> +		return true;
> +
> +	if (mt == MIGRATE_CMA || mt == MIGRATE_ISOLATE)
> +		return false;
> +#endif
> +	/* The zero page can be "pinned" but gets special handling. */
> +	if (is_zero_folio(folio))
> +		return true;
> +
> +	/* Coherent device memory must always allow eviction. */
> +	if (folio_is_device_coherent(folio))
> +		return false;
> +
> +	/*
> +	 * Filesystems can only tolerate transient delays to truncate and
> +	 * hole-punch operations
> +	 */
> +	if (folio_is_fsdax(folio))
> +		return false;
> +
> +	/* Otherwise, non-movable zone folios can be pinned. */
> +	return !folio_is_zone_movable(folio);
> +}
> +
> /*
>  * An array of either pages or folios ("pofs"). Although it may seem tempting to
>  * avoid this complication, by simply interpreting a list of folios as a list of
> -- 
> 2.54.0
> 

Re: [PATCH v2 2/4] mm: gup: allow long-term pins of CMA-allocated HugeTLB folios

[Oscar Salvador (SUSE)]

On Thu, Nov 05, 2026 at 12:07:44PM +0800, Qi Zheng wrote:
> From: Qi Zheng <zhengqi.arch@bytedance.com>
> 
> Long-term pinning treats explicitly CMA-allocated HugeTLB folios as
> unpinnable, causing unnecessary migration or pinning failures.
> 
> These folios already own their CMA bitmap ranges, and memory blocks
> overlapping CMA areas cannot be offlined. Allow HugeTLB folios with
> HPG_cma to be pinned directly, including in ZONE_MOVABLE.
> 
> Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic hugepages using cma")
> Cc: stable@vger.kernel.org
> Suggested-by: Muchun Song <muchun.song@linux.dev>
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

With the rewording suggested by Munchun:

Reviewed-by: Oscar Salvador <osalvador@suse.de>

 

-- 
Oscar Salvador
SUSE Labs

Re: [PATCH v2 2/4] mm: gup: allow long-term pins of CMA-allocated HugeTLB folios

[Jose A. Perez de Azpillaga]

On 11/5/26 5:07 AM, Qi Zheng wrote:
> From: Qi Zheng <zhengqi.arch@bytedance.com>
> 
> Long-term pinning treats explicitly CMA-allocated HugeTLB folios as
> unpinnable, causing unnecessary migration or pinning failures.
> 
> These folios already own their CMA bitmap ranges, and memory blocks
> overlapping CMA areas cannot be offlined. Allow HugeTLB folios with
> HPG_cma to be pinned directly, including in ZONE_MOVABLE.
> 
> Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic hugepages using cma")
> Cc: stable@vger.kernel.org
> Suggested-by: Muchun Song <muchun.song@linux.dev>
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>


LGTM:

Reviewed-by: Jose A. Perez de Azpillaga <azpijr@gmail.com>

-- 
cheers,
jose a. p-a

[PATCH v2 3/4] mm: hugetlb: fix GFP mask propagation to CMA

[Qi Zheng]

From: Qi Zheng <zhengqi.arch@bytedance.com>

cma_alloc_frozen_compound() uses GFP_KERNEL, allowing direct reclaim
during the first MPOL_PREFERRED_MANY allocation attempt even though
the caller clears __GFP_DIRECT_RECLAIM.

Pass the caller's GFP mask through the helper so CMA respects its
reclaim constraints when trying the preferred nodes.

Fixes: 9bda131c6093 ("mm: cma: add cma_alloc_frozen{_compound}()")
Cc: stable@vger.kernel.org
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 include/linux/cma.h | 2 +-
 mm/cma.c            | 4 ++--
 mm/hugetlb_cma.c    | 4 ++--
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/linux/cma.h b/include/linux/cma.h
index 8555d38a97b1a..4539ea5f2c4e8 100644
--- a/include/linux/cma.h
+++ b/include/linux/cma.h
@@ -53,7 +53,7 @@ extern bool cma_release(struct cma *cma, const struct page *pages, unsigned long
 
 struct page *cma_alloc_frozen(struct cma *cma, unsigned long count,
 		unsigned int align, bool no_warn);
-struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order);
+struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order, gfp_t gfp);
 bool cma_release_frozen(struct cma *cma, const struct page *pages,
 		unsigned long count);
 
diff --git a/mm/cma.c b/mm/cma.c
index 9ec1d1fd5dff5..876635a56180e 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -933,9 +933,9 @@ struct page *cma_alloc_frozen(struct cma *cma, unsigned long count,
 	return __cma_alloc_frozen(cma, count, align, gfp);
 }
 
-struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order)
+struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order, gfp_t gfp)
 {
-	gfp_t gfp = GFP_KERNEL | __GFP_COMP | __GFP_NOWARN;
+	gfp |= __GFP_COMP | __GFP_NOWARN;
 
 	return __cma_alloc_frozen(cma, 1 << order, order, gfp);
 }
diff --git a/mm/hugetlb_cma.c b/mm/hugetlb_cma.c
index 80b2407e9f077..307e5736ecdbe 100644
--- a/mm/hugetlb_cma.c
+++ b/mm/hugetlb_cma.c
@@ -69,14 +69,14 @@ struct folio *hugetlb_cma_alloc_frozen_folio(int order, gfp_t gfp_mask,
 	}
 
 	if (hugetlb_cma[nid] && node_isset(nid, *nmask))
-		page = cma_alloc_frozen_compound(hugetlb_cma[nid], order);
+		page = cma_alloc_frozen_compound(hugetlb_cma[nid], order, gfp_mask);
 
 	if (!page && !(gfp_mask & __GFP_THISNODE)) {
 		for_each_node_mask(node, *nmask) {
 			if (node == nid || !hugetlb_cma[node])
 				continue;
 
-			page = cma_alloc_frozen_compound(hugetlb_cma[node], order);
+			page = cma_alloc_frozen_compound(hugetlb_cma[node], order, gfp_mask);
 			if (page)
 				break;
 		}
-- 
2.54.0

Re: [PATCH v2 3/4] mm: hugetlb: fix GFP mask propagation to CMA

[Muchun Song]

> On Nov 5, 2026, at 12:07, Qi Zheng <qi.zheng@linux.dev> wrote:
> 
> From: Qi Zheng <zhengqi.arch@bytedance.com>
> 
> cma_alloc_frozen_compound() uses GFP_KERNEL, allowing direct reclaim
> during the first MPOL_PREFERRED_MANY allocation attempt even though
> the caller clears __GFP_DIRECT_RECLAIM.
> 
> Pass the caller's GFP mask through the helper so CMA respects its
> reclaim constraints when trying the preferred nodes.

More natural.

> 
> Fixes: 9bda131c6093 ("mm: cma: add cma_alloc_frozen{_compound}()")
> Cc: stable@vger.kernel.org
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Acked-by: Muchun Song <muchun.song@linux.dev>

Thanks.

Re: [PATCH v2 3/4] mm: hugetlb: fix GFP mask propagation to CMA

[Oscar Salvador (SUSE)]

On Thu, Nov 05, 2026 at 12:07:45PM +0800, Qi Zheng wrote:
> From: Qi Zheng <zhengqi.arch@bytedance.com>
> 
> cma_alloc_frozen_compound() uses GFP_KERNEL, allowing direct reclaim
> during the first MPOL_PREFERRED_MANY allocation attempt even though
> the caller clears __GFP_DIRECT_RECLAIM.
> 
> Pass the caller's GFP mask through the helper so CMA respects its
> reclaim constraints when trying the preferred nodes.
> 
> Fixes: 9bda131c6093 ("mm: cma: add cma_alloc_frozen{_compound}()")
> Cc: stable@vger.kernel.org
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
...
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -933,9 +933,9 @@ struct page *cma_alloc_frozen(struct cma *cma, unsigned long count,
>  	return __cma_alloc_frozen(cma, count, align, gfp);
>  }
>  
> -struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order)
> +struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order, gfp_t gfp)
>  {
> -	gfp_t gfp = GFP_KERNEL | __GFP_COMP | __GFP_NOWARN;
> +	gfp |= __GFP_COMP | __GFP_NOWARN;

Do we really need __GFP_COMP | __GFP_NOWARN here?
It is my understanding that all allocations coming from hugetlb are
handled with htlb_alloc_mask(), and that should already provide
__GFP_COMP | __GFP_NOWARN.
We might have needed it when cma_alloc_frozen_compound() constructed its
own mask, but not it gets it from the caller, and that should have been
done via htlb_alloc_mask() up the chain.

So, any reason to have it here now?

 

-- 
Oscar Salvador
SUSE Labs

Re: [PATCH v2 3/4] mm: hugetlb: fix GFP mask propagation to CMA

[Jose A. Perez de Azpillaga]

On 11/5/26 5:07 AM, Qi Zheng wrote:
> From: Qi Zheng <zhengqi.arch@bytedance.com>
> 
> cma_alloc_frozen_compound() uses GFP_KERNEL, allowing direct reclaim
> during the first MPOL_PREFERRED_MANY allocation attempt even though
> the caller clears __GFP_DIRECT_RECLAIM.
> 
> Pass the caller's GFP mask through the helper so CMA respects its
> reclaim constraints when trying the preferred nodes.
> 
> Fixes: 9bda131c6093 ("mm: cma: add cma_alloc_frozen{_compound}()")
> Cc: stable@vger.kernel.org
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

LGTM:

Reviewed-by: Jose A. Perez de Azpillaga <azpijr@gmail.com>

-- 
cheers,
jose a. p-a

[PATCH v2 4/4] mm: hugetlb: fix cpuset violations in gigantic surplus allocations

[Qi Zheng]

From: Qi Zheng <zhengqi.arch@bytedance.com>

CMA and the contiguous allocator trust a supplied nodemask without
checking the current cpuset. Gigantic surplus allocations can therefore
use nodes forbidden to the faulting thread.

For example, moving a non-leader thread to another cgroup v1 cpuset
updates its mems_allowed without rebinding the shared VMA policy:

  CPU0 (cpuset attach)             CPU1 (thread T)
  -------------------             ---------------
  T->mems_allowed = {0}
  /* Skip mpol_rebind_mm()
     for a non-leader. */
                                  /* VMA MPOL_BIND remains {0,1}. */
                                  hugetlb_cma_alloc_frozen_folio()
                                    /* node0 fails; node1 succeeds. */

Intersect the allocation mask with the current cpuset, preserving
MPOL_BIND and MPOL_PREFERRED_MANY fallback rules. Retry only failed
allocations when the cpuset changes.

Fixes: eb02f14c4a2b ("mm/hugetlb: allow overcommitting gigantic hugepages")
Cc: stable@vger.kernel.org
Reported-by: Lance Yang <lance.yang@linux.dev>
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 mm/hugetlb.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 6fba92b0f6749..09b64f7c11dd2 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2181,22 +2181,33 @@ struct folio *alloc_buddy_hugetlb_folio(struct hstate *h,
 		gfp_t gfp_mask, struct mempolicy_interpreted *mpoli)
 {
 	struct folio *folio = NULL;
-	nodemask_t *nodemask = mpoli->nodemask;
+	nodemask_t alloc_nodemask;
+	unsigned int cpuset_mems_cookie;
+
+retry:
+	cpuset_mems_cookie = read_mems_allowed_begin();
+	alloc_nodemask = cpuset_current_mems_allowed;
+	if (mpoli->mode == MPOL_BIND && mpoli->nodemask &&
+	    nodes_intersects(*mpoli->nodemask, alloc_nodemask))
+		nodes_and(alloc_nodemask, alloc_nodemask, *mpoli->nodemask);
 
 	if (mpoli->mode == MPOL_PREFERRED_MANY) {
 		gfp_t gfp = gfp_mask & ~(__GFP_DIRECT_RECLAIM | __GFP_NOFAIL);
 
+		nodes_and(alloc_nodemask, alloc_nodemask, *mpoli->nodemask);
 		folio = alloc_surplus_hugetlb_folio(h, gfp, mpoli->nid,
-						    nodemask);
+						    &alloc_nodemask);
 
-		/* Fallback to all nodes if page==NULL */
-		nodemask = NULL;
+		/* Fallback to all nodes allowed by the current cpuset */
+		alloc_nodemask = cpuset_current_mems_allowed;
 	}
 
-	if (!folio) {
+	if (!folio)
 		folio = alloc_surplus_hugetlb_folio(h, gfp_mask, mpoli->nid,
-						    nodemask);
-	}
+						    &alloc_nodemask);
+
+	if (!folio && unlikely(read_mems_allowed_retry(cpuset_mems_cookie)))
+		goto retry;
 
 	return folio;
 }
-- 
2.54.0