linux-kernel - Re: [PATCH v2 2/3] mm: use folio_add_new_anon_rmap() if folio_test

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]

Date: Thu, 20 Jun 2024 09:46:17 +0200
From: David Hildenbrand <david@...hat.com>
To: Barry Song <21cnbao@...il.com>, akpm@...ux-foundation.org,
 linux-mm@...ck.org
Cc: baolin.wang@...ux.alibaba.com, chrisl@...nel.org,
 linux-kernel@...r.kernel.org, mhocko@...e.com, ryan.roberts@....com,
 shy828301@...il.com, surenb@...gle.com, v-songbaohua@...o.com,
 willy@...radead.org, ying.huang@...el.com, yosryahmed@...gle.com,
 yuzhao@...gle.com, Shuai Yuan <yuanshuai@...o.com>
Subject: Re: [PATCH v2 2/3] mm: use folio_add_new_anon_rmap() if
 folio_test_anon(folio)==false

On 18.06.24 01:11, Barry Song wrote:
> From: Barry Song <v-songbaohua@...o.com>
> 
> For the !folio_test_anon(folio) case, we can now invoke folio_add_new_anon_rmap()
> with the rmap flags set to either EXCLUSIVE or non-EXCLUSIVE. This action will
> suppress the VM_WARN_ON_FOLIO check within __folio_add_anon_rmap() while initiating
> the process of bringing up mTHP swapin.
> 
>   static __always_inline void __folio_add_anon_rmap(struct folio *folio,
>                   struct page *page, int nr_pages, struct vm_area_struct *vma,
>                   unsigned long address, rmap_t flags, enum rmap_level level)
>   {
>           ...
>           if (unlikely(!folio_test_anon(folio))) {
>                   VM_WARN_ON_FOLIO(folio_test_large(folio) &&
>                                    level != RMAP_LEVEL_PMD, folio);
>           }
>           ...
>   }
> 
> It also improves the code’s readability. Currently, all new anonymous
> folios calling folio_add_anon_rmap_ptes() are order-0. This ensures
> that new folios cannot be partially exclusive; they are either entirely
> exclusive or entirely shared.
> 
> Suggested-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Barry Song <v-songbaohua@...o.com>
> Tested-by: Shuai Yuan <yuanshuai@...o.com>
> ---
>   mm/memory.c   |  8 ++++++++
>   mm/swapfile.c | 13 +++++++++++--
>   2 files changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index 1f24ecdafe05..620654c13b2f 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4339,6 +4339,14 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>   	if (unlikely(folio != swapcache && swapcache)) {
>   		folio_add_new_anon_rmap(folio, vma, address, RMAP_EXCLUSIVE);
>   		folio_add_lru_vma(folio, vma);
> +	} else if (!folio_test_anon(folio)) {
> +		/*
> +		 * We currently only expect small !anon folios, for which we now
> +		 * that they are either fully exclusive or fully shared. If we
> +		 * ever get large folios here, we have to be careful.
> +		 */
> +		VM_WARN_ON_ONCE(folio_test_large(folio));
> +		folio_add_new_anon_rmap(folio, vma, address, rmap_flags);
>   	} else {
>   		folio_add_anon_rmap_ptes(folio, page, nr_pages, vma, address,
>   					rmap_flags);
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index ae1d2700f6a3..69efa1a57087 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1908,8 +1908,17 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
>   		VM_BUG_ON_FOLIO(folio_test_writeback(folio), folio);
>   		if (pte_swp_exclusive(old_pte))
>   			rmap_flags |= RMAP_EXCLUSIVE;
> -
> -		folio_add_anon_rmap_pte(folio, page, vma, addr, rmap_flags);
> +		/*
> +		 * We currently only expect small !anon folios, for which we now that
> +		 * they are either fully exclusive or fully shared. If we ever get
> +		 * large folios here, we have to be careful.
> +		 */
> +		if (!folio_test_anon(folio)) {
> +			VM_WARN_ON_ONCE(folio_test_large(folio));

(comment applies to both cases)

Thinking about Hugh's comment, we should likely add here:

VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio);

[the check we are removing from __folio_add_anon_rmap()]

and document for folio_add_new_anon_rmap() in patch #1, that when 
dealing with folios that might be mapped concurrently by others, the 
folio lock must be held.

> +			folio_add_new_anon_rmap(folio, vma, addr, rmap_flags);
> +		} else {
> +			folio_add_anon_rmap_pte(folio, page, vma, addr, rmap_flags);
> +		}
>   	} else { /* ksm created a completely new copy */
>   		folio_add_new_anon_rmap(folio, vma, addr, RMAP_EXCLUSIVE);
>   		folio_add_lru_vma(folio, vma);

-- 
Cheers,

David / dhildenb