linux-kernel - Re: [PATCH v4 18/25] gup: Don't allow FOLL

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Message-ID: <e7f9433e-bd4b-4284-990b-9ea074064f0a@redhat.com>
Date: Tue, 17 Dec 2024 23:33:09 +0100
From: David Hildenbrand <david@...hat.com>
To: Alistair Popple <apopple@...dia.com>, akpm@...ux-foundation.org,
 dan.j.williams@...el.com, linux-mm@...ck.org
Cc: lina@...hilina.net, zhang.lyra@...il.com, gerald.schaefer@...ux.ibm.com,
 vishal.l.verma@...el.com, dave.jiang@...el.com, logang@...tatee.com,
 bhelgaas@...gle.com, jack@...e.cz, jgg@...pe.ca, catalin.marinas@....com,
 will@...nel.org, mpe@...erman.id.au, npiggin@...il.com,
 dave.hansen@...ux.intel.com, ira.weiny@...el.com, willy@...radead.org,
 djwong@...nel.org, tytso@....edu, linmiaohe@...wei.com, peterx@...hat.com,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
 nvdimm@...ts.linux.dev, linux-cxl@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
 linux-xfs@...r.kernel.org, jhubbard@...dia.com, hch@....de,
 david@...morbit.com
Subject: Re: [PATCH v4 18/25] gup: Don't allow FOLL_LONGTERM pinning of FS DAX
 pages

On 17.12.24 06:13, Alistair Popple wrote:
> Longterm pinning of FS DAX pages should already be disallowed by
> various pXX_devmap checks. However a future change will cause these
> checks to be invalid for FS DAX pages so make
> folio_is_longterm_pinnable() return false for FS DAX pages.

Nit: I'd consistently use "mm/gup:" as prefix for GUP-related patches. 
(similarly, mm/huge_memory and mm/rmap in the other patches)

> 
> Signed-off-by: Alistair Popple <apopple@...dia.com>
> Reviewed-by: John Hubbard <jhubbard@...dia.com>
> ---
>   include/linux/mm.h | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index f267b06..01edca9 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2078,6 +2078,10 @@ static inline bool folio_is_longterm_pinnable(struct folio *folio)
>   	if (folio_is_device_coherent(folio))
>   		return false;
>   
> +	/* DAX must also always allow eviction. */
> +	if (folio_is_fsdax(folio))
> +		return false;
> +
>   	/* Otherwise, non-movable zone folios can be pinned. */
>   	return !folio_is_zone_movable(folio);
>   

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb