[v1] mm: remove nth_page()

[PATCH v1 07/36] mm/memremap: reject unreasonable folio/compound page sizes in memremap_pages()

Posted by David Hildenbrand 1 month ago

Let's reject unreasonable folio sizes early, where we can still fail.
We'll add sanity checks to prepare_compound_head/prepare_compound_page
next.

Is there a way to configure a system such that unreasonable folio sizes
would be possible? It would already be rather questionable.

If so, we'd probably want to bail out earlier, where we can avoid a
WARN and just report a proper error message that indicates where
something went wrong such that we messed up.

Acked-by: SeongJae Park <sj@kernel.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/memremap.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/memremap.c b/mm/memremap.c
index b0ce0d8254bd8..a2d4bb88f64b6 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -275,6 +275,9 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
 
 	if (WARN_ONCE(!nr_range, "nr_range must be specified\n"))
 		return ERR_PTR(-EINVAL);
+	if (WARN_ONCE(pgmap->vmemmap_shift > MAX_FOLIO_ORDER,
+		      "requested folio size unsupported\n"))
+		return ERR_PTR(-EINVAL);
 
 	switch (pgmap->type) {
 	case MEMORY_DEVICE_PRIVATE:
-- 
2.50.1

Re: [PATCH v1 07/36] mm/memremap: reject unreasonable folio/compound page sizes in memremap_pages()

Posted by Liam R. Howlett 1 month ago

* David Hildenbrand <david@redhat.com> [250827 18:04]:
> Let's reject unreasonable folio sizes early, where we can still fail.
> We'll add sanity checks to prepare_compound_head/prepare_compound_page
> next.
> 
> Is there a way to configure a system such that unreasonable folio sizes
> would be possible? It would already be rather questionable.
> 
> If so, we'd probably want to bail out earlier, where we can avoid a
> WARN and just report a proper error message that indicates where
> something went wrong such that we messed up.
> 
> Acked-by: SeongJae Park <sj@kernel.org>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>

> ---
>  mm/memremap.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/memremap.c b/mm/memremap.c
> index b0ce0d8254bd8..a2d4bb88f64b6 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -275,6 +275,9 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
>  
>  	if (WARN_ONCE(!nr_range, "nr_range must be specified\n"))
>  		return ERR_PTR(-EINVAL);
> +	if (WARN_ONCE(pgmap->vmemmap_shift > MAX_FOLIO_ORDER,
> +		      "requested folio size unsupported\n"))
> +		return ERR_PTR(-EINVAL);
>  
>  	switch (pgmap->type) {
>  	case MEMORY_DEVICE_PRIVATE:
> -- 
> 2.50.1
>

Re: [PATCH v1 07/36] mm/memremap: reject unreasonable folio/compound page sizes in memremap_pages()

Posted by Lorenzo Stoakes 1 month ago

On Thu, Aug 28, 2025 at 12:01:11AM +0200, David Hildenbrand wrote:
> Let's reject unreasonable folio sizes early, where we can still fail.
> We'll add sanity checks to prepare_compound_head/prepare_compound_page
> next.
>
> Is there a way to configure a system such that unreasonable folio sizes
> would be possible? It would already be rather questionable.
>
> If so, we'd probably want to bail out earlier, where we can avoid a
> WARN and just report a proper error message that indicates where
> something went wrong such that we messed up.
>
> Acked-by: SeongJae Park <sj@kernel.org>
> Signed-off-by: David Hildenbrand <david@redhat.com>

LGTM, so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

> ---
>  mm/memremap.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/mm/memremap.c b/mm/memremap.c
> index b0ce0d8254bd8..a2d4bb88f64b6 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -275,6 +275,9 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
>
>  	if (WARN_ONCE(!nr_range, "nr_range must be specified\n"))
>  		return ERR_PTR(-EINVAL);
> +	if (WARN_ONCE(pgmap->vmemmap_shift > MAX_FOLIO_ORDER,
> +		      "requested folio size unsupported\n"))
> +		return ERR_PTR(-EINVAL);
>
>  	switch (pgmap->type) {
>  	case MEMORY_DEVICE_PRIVATE:
> --
> 2.50.1
>