From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 98D6719AD70 for ; Wed, 6 Aug 2025 11:19:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754479182; cv=none; b=te5nQ7OAtNVG8fYD376RkWbDulVuYceMF39D87hK+HgZ4oKm0SJEPQV3a0Yfm9nKQYUjDtRqjgNQsB2ar2bBu3fKqa7tsE62/SBgt3y6bpiTsVR5hn04i/Qljter5kNpgVuBcc9oKTCNdDWhpp8atgdmcPwCnwgbgS1y4m5UwQs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754479182; c=relaxed/simple; bh=IeE2uatGLfcgmOPjF1H8GEYdPcamsQmpqFWUsOVOMiI=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=qNhuHHG5GqUO+hBkFGQdrDSRKW6lkK2OHdXqSYS/7ik+bICRkykQCE9HJ01wvS2A8ENh34KXAYIaLPGKSvUKpwb1Y8BYeRGwqyQH9R9EDhR32yebd1JwbUbslbFvA56mka5Ai3zupFkEVYMVLTHWgiNJIA/QSuBPpwtZVb7WgB8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6CF0919F0; Wed, 6 Aug 2025 04:19:26 -0700 (PDT) Received: from MacBook-Pro.blr.arm.com (unknown [10.164.18.68]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id A029E3F5A1; Wed, 6 Aug 2025 04:19:31 -0700 (PDT) From: Dev Jain To: syzbot+57bcc752f0df8bb1365c@syzkaller.appspotmail.com Cc: akpm@linux-foundation.org, david@redhat.com, jgg@ziepe.ca, jhubbard@nvidia.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, peterx@redhat.com, syzkaller-bugs@googlegroups.com, Dev Jain Subject: Re: [syzbot] [mm?] WARNING in follow_page_pte Date: Wed, 6 Aug 2025 16:49:22 +0530 Message-Id: <20250806111922.669-1-dev.jain@arm.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <68930511.050a0220.7f033.003a.GAE@google.com> References: <68930511.050a0220.7f033.003a.GAE@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit #syz test In commit_anon_folio_batch(), we iterate over all pages pointed to by the PTE batch. Therefore we need to know the first page of the batch; currently we derive that via folio_page(folio, 0), but, that takes us to the first (head) page of the folio instead - our PTE batch may lie in the middle of the folio, leading to incorrectness. Bite the bullet and throw away the micro-optimization of reusing the folio in favour of code simplicity. Derive the page and the folio in change_pte_range, and pass the page too to commit_anon_folio_batch to fix the aforementioned issue. Also, instead of directly adding to the stuct page *page pointer, use the nth_page() macro for safety. Fixes: cac1db8c3aad ("mm: optimize mprotect() by PTE batching") Signed-off-by: Dev Jain --- mm/mprotect.c | 25 +++++++++++-------------- 1 file changed, 11 insertions(+), 14 deletions(-) diff --git a/mm/mprotect.c b/mm/mprotect.c index 78bded7acf79..96cd36ed3489 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -120,9 +120,8 @@ static int mprotect_folio_pte_batch(struct folio *folio, pte_t *ptep, static bool prot_numa_skip(struct vm_area_struct *vma, unsigned long addr, pte_t oldpte, pte_t *pte, int target_node, - struct folio **foliop) + struct folio *folio) { - struct folio *folio = NULL; bool ret = true; bool toptier; int nid; @@ -131,7 +130,6 @@ static bool prot_numa_skip(struct vm_area_struct *vma, unsigned long addr, if (pte_protnone(oldpte)) goto skip; - folio = vm_normal_folio(vma, addr, oldpte); if (!folio) goto skip; @@ -173,7 +171,6 @@ static bool prot_numa_skip(struct vm_area_struct *vma, unsigned long addr, folio_xchg_access_time(folio, jiffies_to_msecs(jiffies)); skip: - *foliop = folio; return ret; } @@ -231,16 +228,15 @@ static int page_anon_exclusive_sub_batch(int start_idx, int max_len, * retrieve sub-batches. */ static void commit_anon_folio_batch(struct vm_area_struct *vma, - struct folio *folio, unsigned long addr, pte_t *ptep, + struct folio *folio, struct page *first_page, unsigned long addr, pte_t *ptep, pte_t oldpte, pte_t ptent, int nr_ptes, struct mmu_gather *tlb) { - struct page *first_page = folio_page(folio, 0); bool expected_anon_exclusive; int sub_batch_idx = 0; int len; while (nr_ptes) { - expected_anon_exclusive = PageAnonExclusive(first_page + sub_batch_idx); + expected_anon_exclusive = PageAnonExclusive(nth_page(first_page, sub_batch_idx)); len = page_anon_exclusive_sub_batch(sub_batch_idx, nr_ptes, first_page, expected_anon_exclusive); prot_commit_flush_ptes(vma, addr, ptep, oldpte, ptent, len, @@ -251,7 +247,7 @@ static void commit_anon_folio_batch(struct vm_area_struct *vma, } static void set_write_prot_commit_flush_ptes(struct vm_area_struct *vma, - struct folio *folio, unsigned long addr, pte_t *ptep, + struct folio *folio, struct page *page, unsigned long addr, pte_t *ptep, pte_t oldpte, pte_t ptent, int nr_ptes, struct mmu_gather *tlb) { bool set_write; @@ -270,7 +266,7 @@ static void set_write_prot_commit_flush_ptes(struct vm_area_struct *vma, /* idx = */ 0, set_write, tlb); return; } - commit_anon_folio_batch(vma, folio, addr, ptep, oldpte, ptent, nr_ptes, tlb); + commit_anon_folio_batch(vma, folio, page, addr, ptep, oldpte, ptent, nr_ptes, tlb); } static long change_pte_range(struct mmu_gather *tlb, @@ -305,15 +301,19 @@ static long change_pte_range(struct mmu_gather *tlb, const fpb_t flags = FPB_RESPECT_SOFT_DIRTY | FPB_RESPECT_WRITE; int max_nr_ptes = (end - addr) >> PAGE_SHIFT; struct folio *folio = NULL; + struct page *page; pte_t ptent; + page = vm_normal_page(vma, addr, oldpte); + if (page) + folio = page_folio(page); /* * Avoid trapping faults against the zero or KSM * pages. See similar comment in change_huge_pmd. */ if (prot_numa) { int ret = prot_numa_skip(vma, addr, oldpte, pte, - target_node, &folio); + target_node, folio); if (ret) { /* determine batch to skip */ @@ -323,9 +323,6 @@ static long change_pte_range(struct mmu_gather *tlb, } } - if (!folio) - folio = vm_normal_folio(vma, addr, oldpte); - nr_ptes = mprotect_folio_pte_batch(folio, pte, oldpte, max_nr_ptes, flags); oldpte = modify_prot_start_ptes(vma, addr, pte, nr_ptes); @@ -351,7 +348,7 @@ static long change_pte_range(struct mmu_gather *tlb, */ if ((cp_flags & MM_CP_TRY_CHANGE_WRITABLE) && !pte_write(ptent)) - set_write_prot_commit_flush_ptes(vma, folio, + set_write_prot_commit_flush_ptes(vma, folio, page, addr, pte, oldpte, ptent, nr_ptes, tlb); else prot_commit_flush_ptes(vma, addr, pte, oldpte, ptent, -- 2.30.2