linux-kernel - Re: [PATCH 1/4] mm: Trial do_wp

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 for Android: free password hash cracker in your pocket

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

Message-ID: <20200915150349.GA22415@redhat.com>
Date:   Tue, 15 Sep 2020 17:03:49 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "Maya B . Gokhale" <gokhale2@...l.gov>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Marty Mcfadden <mcfadden8@...l.gov>,
        Kirill Shutemov <kirill@...temov.name>,
        Jann Horn <jannh@...gle.com>, Jan Kara <jack@...e.cz>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/4] mm: Trial do_wp_page() simplification

On 08/21, Peter Xu wrote:
>
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2927,50 +2927,25 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
>  	 * not dirty accountable.
>  	 */
>  	if (PageAnon(vmf->page)) {
> -		int total_map_swapcount;
> -		if (PageKsm(vmf->page) && (PageSwapCache(vmf->page) ||
> -					   page_count(vmf->page) != 1))
> +		struct page *page = vmf->page;
> +
> +		/* PageKsm() doesn't necessarily raise the page refcount */
> +		if (PageKsm(page) || page_count(page) != 1)
> +			goto copy;
> +		if (!trylock_page(page))
> +			goto copy;
> +		if (PageKsm(page) || page_mapcount(page) != 1 || page_count(page) != 1) {
> +			unlock_page(page);
>  			goto copy;
> -		if (!trylock_page(vmf->page)) {
> -			get_page(vmf->page);
> -			pte_unmap_unlock(vmf->pte, vmf->ptl);
> -			lock_page(vmf->page);
> -			vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
> -					vmf->address, &vmf->ptl);
> -			if (!pte_same(*vmf->pte, vmf->orig_pte)) {
> -				update_mmu_tlb(vma, vmf->address, vmf->pte);
> -				unlock_page(vmf->page);
> -				pte_unmap_unlock(vmf->pte, vmf->ptl);
> -				put_page(vmf->page);
> -				return 0;
> -			}
> -			put_page(vmf->page);
> -		}
> -		if (PageKsm(vmf->page)) {
> -			bool reused = reuse_ksm_page(vmf->page, vmf->vma,
> -						     vmf->address);
> -			unlock_page(vmf->page);
> -			if (!reused)
> -				goto copy;
> -			wp_page_reuse(vmf);
> -			return VM_FAULT_WRITE;
> -		}
> -		if (reuse_swap_page(vmf->page, &total_map_swapcount)) {

It seems that nobody else calls reuse_swap_page() with total_map_swapcount != NULL.

Oleg.