linux-kernel - Re: [PATCH v1 07/36] mm/memremap: reject unreasonable folio/compound page sizes in memremap

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Message-ID: <29226dad-e119-4727-9e23-dc7c527e4281@lucifer.local>
Date: Thu, 28 Aug 2025 15:39:40 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, SeongJae Park <sj@...nel.org>,
        Alexander Potapenko <glider@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brendan Jackman <jackmanb@...gle.com>,
        Christoph Lameter <cl@...two.org>, Dennis Zhou <dennis@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>, dri-devel@...ts.freedesktop.org,
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Subject: Re: [PATCH v1 07/36] mm/memremap: reject unreasonable folio/compound
 page sizes in memremap_pages()

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@...nel.org>
> Signed-off-by: David Hildenbrand <david@...hat.com>

LGTM, so:

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