From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id 871E66B0033 for ; Wed, 25 Jan 2017 18:09:16 -0500 (EST) Received: by mail-pf0-f198.google.com with SMTP id f144so286967784pfa.3 for ; Wed, 25 Jan 2017 15:09:16 -0800 (PST) Received: from lgeamrelo12.lge.com (LGEAMRELO12.lge.com. [156.147.23.52]) by mx.google.com with ESMTP id f6si2968461plj.124.2017.01.25.15.09.14 for ; Wed, 25 Jan 2017 15:09:15 -0800 (PST) Date: Thu, 26 Jan 2017 08:09:09 +0900 From: Minchan Kim Subject: Re: [PATCH] mm: write protect MADV_FREE pages Message-ID: <20170125230909.GA20811@bbox> References: <791151284cd6941296f08488b8cb7f1968175a0a.1485212872.git.shli@fb.com> <20170124023212.GA24523@bbox> <20170125171429.5vbqizijrhav522d@kernel.org> MIME-Version: 1.0 In-Reply-To: <20170125171429.5vbqizijrhav522d@kernel.org> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline Sender: owner-linux-mm@kvack.org List-ID: To: Shaohua Li Cc: Shaohua Li , linux-mm@kvack.org, Kernel-team@fb.com, Andrew Morton , Hugh Dickins , Rik van Riel , Mel Gorman Hello, On Wed, Jan 25, 2017 at 09:15:19AM -0800, Shaohua Li wrote: > On Tue, Jan 24, 2017 at 11:32:12AM +0900, Minchan Kim wrote: > > 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? > Sorry for the delay, for some reason, I didn't receive the mail. > in try_to_unmap_one: > CPU 1: CPU2: > 1. pteval = ptep_get_and_clear(mm, address, pte); > 2. write to the address > 3. tlb flush > > step 1 will get a clean pteval, step2 dirty it, but the unmap missed the dirty > bit so discard the page without pageout. step2 doesn't trigger a page fault, I thought about that when Mel introduced deferred flush and concluded it should be no problem from theses discussion: 1. https://lkml.org/lkml/2015/4/15/565 2. https://lkml.org/lkml/2015/4/16/136 So, shouldn't it make trap? Ccing Mel. > because the tlb cache still has the pte entry. The defer flush makes the window > bigger actually. There are comments about this in try_to_unmap_one too. > > Thanks, > Shaohua > > > > 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 > > -- > 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