From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f72.google.com (mail-pg0-f72.google.com [74.125.83.72]) by kanga.kvack.org (Postfix) with ESMTP id 2390A6B0033 for ; Mon, 23 Jan 2017 21:32:16 -0500 (EST) Received: by mail-pg0-f72.google.com with SMTP id d185so219933009pgc.2 for ; Mon, 23 Jan 2017 18:32:16 -0800 (PST) Received: from lgeamrelo13.lge.com (LGEAMRELO13.lge.com. [156.147.23.53]) by mx.google.com with ESMTP id v128si17470271pgv.72.2017.01.23.18.32.14 for ; Mon, 23 Jan 2017 18:32:15 -0800 (PST) Date: Tue, 24 Jan 2017 11:32:12 +0900 From: Minchan Kim Subject: Re: [PATCH] mm: write protect MADV_FREE pages Message-ID: <20170124023212.GA24523@bbox> References: <791151284cd6941296f08488b8cb7f1968175a0a.1485212872.git.shli@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <791151284cd6941296f08488b8cb7f1968175a0a.1485212872.git.shli@fb.com> Sender: owner-linux-mm@kvack.org List-ID: To: Shaohua Li Cc: linux-mm@kvack.org, Kernel-team@fb.com, Andrew Morton , Hugh Dickins , Rik van Riel , stable@kernel.org Hi Shaohua, On Mon, Jan 23, 2017 at 03:15:52PM -0800, Shaohua Li wrote: > The page reclaim has an assumption writting to a page with clean pte > should trigger a page fault, because there is a window between pte zero > and tlb flush where a new write could come. If the new write doesn't > trigger page fault, page reclaim will not notice it and think the page > is clean and reclaim it. The MADV_FREE pages don't comply with the rule > and the pte is just cleaned without writeprotect, so there will be no > pagefault for new write. This will cause data corruption. It's hard to understand. Could you show me exact scenario seqence you have in mind? Thanks. > > Cc: Minchan Kim > Cc: Andrew Morton > Cc: Hugh Dickins > Cc: Rik van Riel > Cc: stable@kernel.org > Signed-off-by: Shaohua Li > --- > mm/huge_memory.c | 1 + > mm/madvise.c | 1 + > 2 files changed, 2 insertions(+) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 9a6bd6c..9cc5de5 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1381,6 +1381,7 @@ bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, > tlb->fullmm); > orig_pmd = pmd_mkold(orig_pmd); > orig_pmd = pmd_mkclean(orig_pmd); > + orig_pmd = pmd_wrprotect(orig_pmd); > > set_pmd_at(mm, addr, pmd, orig_pmd); > tlb_remove_pmd_tlb_entry(tlb, pmd, addr); > diff --git a/mm/madvise.c b/mm/madvise.c > index 0e3828e..bfb6800 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -373,6 +373,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, > > ptent = pte_mkold(ptent); > ptent = pte_mkclean(ptent); > + ptent = pte_wrprotect(ptent); > set_pte_at(mm, addr, pte, ptent); > if (PageActive(page)) > deactivate_page(page); > -- > 2.9.3 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org