From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id 9D2E36B025E for ; Mon, 23 Jan 2017 18:28:16 -0500 (EST) Received: by mail-pf0-f200.google.com with SMTP id d134so219920484pfd.0 for ; Mon, 23 Jan 2017 15:28:16 -0800 (PST) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id b27si4583007pgn.86.2017.01.23.15.28.15 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 23 Jan 2017 15:28:15 -0800 (PST) Date: Mon, 23 Jan 2017 15:28:14 -0800 From: Andrew Morton Subject: Re: [PATCH] mm: write protect MADV_FREE pages Message-Id: <20170123152814.2a55c4110df3bd0d67de5fc3@linux-foundation.org> In-Reply-To: <791151284cd6941296f08488b8cb7f1968175a0a.1485212872.git.shli@fb.com> References: <791151284cd6941296f08488b8cb7f1968175a0a.1485212872.git.shli@fb.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Shaohua Li Cc: linux-mm@kvack.org, Kernel-team@fb.com, Minchan Kim , Hugh Dickins , Rik van Riel , stable@kernel.org On Mon, 23 Jan 2017 15:15:52 -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. I'd like to see here a complete description of the bug's effects: waht sort of workload will trigger it, what the end-user visible effects are, etc. > --- 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); Is this the right way round? There's still a window where we won't get that write fault on the cleaned pte. Should the pmd_wrprotect() happen before the pmd_mkclean()? > 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); -- 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