linux-kernel - Re: [PATCH] mm/vma: Do not register private-anon mappings with khugepaged during mmap

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

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <67f0916e-9825-4105-b044-a16c0e82e736@lucifer.local>
Date: Thu, 6 Mar 2025 08:18:26 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Dev Jain <dev.jain@....com>
Cc: akpm@...ux-foundation.org, Liam.Howlett@...cle.com, vbabka@...e.cz,
        jannh@...gle.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        ryan.roberts@....com, anshuman.khandual@....com,
        aneesh.kumar@...nel.org, yang@...amperecomputing.com, david@...hat.com,
        willy@...radead.org, hughd@...gle.com, ziy@...dia.com
Subject: Re: [PATCH] mm/vma: Do not register private-anon mappings with
 khugepaged during mmap

On Thu, Mar 06, 2025 at 12:00:37PM +0530, Dev Jain wrote:
> We already are registering private-anon VMAs with khugepaged during fault
> time, in do_huge_pmd_anonymous_page(). Commit "register suitable readonly
> file vmas for khugepaged" moved the khugepaged registration logic from
> shmem_mmap to the generic mmap path. Make this logic specific for non-anon
> mappings.

This does sound reasonable, thanks! Though does need to be expanded as
Andrew says for user-visible effects just to be crystal clear.

>
> Fixes: 613bec092fe7 ("mm: mmap: register suitable readonly file vmas for khugepaged")
> Signed-off-by: Dev Jain <dev.jain@....com>
> ---
>  mm/vma.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/vma.c b/mm/vma.c
> index af1d549b179c..730a26bf14a5 100644
> --- a/mm/vma.c
> +++ b/mm/vma.c
> @@ -2377,7 +2377,8 @@ static int __mmap_new_vma(struct mmap_state *map, struct vm_area_struct **vmap)
>  	 * vma_merge_new_range() calls khugepaged_enter_vma() too, the below
>  	 * call covers the non-merge case.
>  	 */
> -	khugepaged_enter_vma(vma, map->flags);
> +	if (!vma_is_anonymous(vma))
> +		khugepaged_enter_vma(vma, map->flags);

This really needs a comment :) as a Joe Bloggs coder coming to this my
immediate thought would be 'huh? Why?'

Something like:

	/* Just added so khugepaged has nothing to do. We call again on fault. */

Would be great.

Thanks!


>  	ksm_add_vma(vma);
>  	*vmap = vma;
>  	return 0;
> --
> 2.30.2
>