From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E6346C433EF for ; Tue, 19 Apr 2022 17:41:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1353689AbiDSRnq (ORCPT ); Tue, 19 Apr 2022 13:43:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51880 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1349765AbiDSRnf (ORCPT ); Tue, 19 Apr 2022 13:43:35 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8FBB91D33A for ; Tue, 19 Apr 2022 10:40:52 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id EF817210FD; Tue, 19 Apr 2022 17:40:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1650390051; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NPmQFOC09HGnA6JA0olfRcv8MOi5ek3og/OWW6F6GSg=; b=SfAiQHmZppRAszAHrKvDRwVpZ+ePMmhKpRztXXqApXTnNXFRdT/TYdJur1dI7QxrtuuBGP B03+Xf8S/RdFNQ1J98tKXvGuSYrcrpYHEscUAAoiZtt7ntYOiYpTuRKTp5JRGwAu8vcSdQ yFiP2/ySqmJx46uAiqyeXxUGAso2i18= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1650390051; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NPmQFOC09HGnA6JA0olfRcv8MOi5ek3og/OWW6F6GSg=; b=EoFq89jDHw1SFNtDvGzuCsy0aiuGzdtUGPORWrF14iEe5QZlB/qK0RiaG9ywEAXDLLo1nP DVnh0toZxYdHgLAA== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 846D2139BE; Tue, 19 Apr 2022 17:40:50 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id T11tHyL0XmLDbQAAMHmgww (envelope-from ); Tue, 19 Apr 2022 17:40:50 +0000 Message-ID: Date: Tue, 19 Apr 2022 19:40:50 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: [PATCH v3 16/16] mm/gup: sanity-check with CONFIG_DEBUG_VM that anonymous pages are exclusive when (un)pinning Content-Language: en-US To: David Hildenbrand , linux-kernel@vger.kernel.org Cc: Andrew Morton , Hugh Dickins , Linus Torvalds , David Rientjes , Shakeel Butt , John Hubbard , Jason Gunthorpe , Mike Kravetz , Mike Rapoport , Yang Shi , "Kirill A . Shutemov" , Matthew Wilcox , Jann Horn , Michal Hocko , Nadav Amit , Rik van Riel , Roman Gushchin , Andrea Arcangeli , Peter Xu , Donald Dutile , Christoph Hellwig , Oleg Nesterov , Jan Kara , Liang Zhang , Pedro Gomes , Oded Gabbay , linux-mm@kvack.org References: <20220329160440.193848-1-david@redhat.com> <20220329160440.193848-17-david@redhat.com> From: Vlastimil Babka In-Reply-To: <20220329160440.193848-17-david@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/29/22 18:04, David Hildenbrand wrote: > Let's verify when (un)pinning anonymous pages that we always deal with > exclusive anonymous pages, which guarantees that we'll have a reliable > PIN, meaning that we cannot end up with the GUP pin being inconsistent > with he pages mapped into the page tables due to a COW triggered > by a write fault. > > When pinning pages, after conditionally triggering GUP unsharing of > possibly shared anonymous pages, we should always only see exclusive > anonymous pages. Note that anonymous pages that are mapped writable > must be marked exclusive, otherwise we'd have a BUG. > > When pinning during ordinary GUP, simply add a check after our > conditional GUP-triggered unsharing checks. As we know exactly how the > page is mapped, we know exactly in which page we have to check for > PageAnonExclusive(). > > When pinning via GUP-fast we have to be careful, because we can race with > fork(): verify only after we made sure via the seqcount that we didn't > race with concurrent fork() that we didn't end up pinning a possibly > shared anonymous page. > > Similarly, when unpinning, verify that the pages are still marked as > exclusive: otherwise something turned the pages possibly shared, which > can result in random memory corruptions, which we really want to catch. > > With only the pinned pages at hand and not the actual page table entries > we have to be a bit careful: hugetlb pages are always mapped via a > single logical page table entry referencing the head page and > PG_anon_exclusive of the head page applies. Anon THP are a bit more > complicated, because we might have obtained the page reference either via > a PMD or a PTE -- depending on the mapping type we either have to check > PageAnonExclusive of the head page (PMD-mapped THP) or the tail page > (PTE-mapped THP) applies: as we don't know and to make our life easier, > check that either is set. > > Take care to not verify in case we're unpinning during GUP-fast because > we detected concurrent fork(): we might stumble over an anonymous page > that is now shared. > > Signed-off-by: David Hildenbrand Acked-by: Vlastimil Babka Nits: > @@ -510,6 +563,10 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, > page = ERR_PTR(-EMLINK); > goto out; > } > + > + VM_BUG_ON((flags & FOLL_PIN) && PageAnon(page) && > + !PageAnonExclusive(page)); Do we rather want VM_BUG_ON_PAGE? Also for the same tests in mm/huge*.c below. > + > /* try_grab_page() does nothing unless FOLL_GET or FOLL_PIN is set. */ > if (unlikely(!try_grab_page(page, flags))) { > page = ERR_PTR(-ENOMEM); > @@ -2744,8 +2801,10 @@ static unsigned long lockless_pages_from_mm(unsigned long start, > */ > if (gup_flags & FOLL_PIN) { > if (read_seqcount_retry(¤t->mm->write_protect_seq, seq)) { > - unpin_user_pages(pages, nr_pinned); > + unpin_user_pages_lockless(pages, nr_pinned); > return 0; > + } else { > + sanity_check_pinned_pages(pages, nr_pinned); > } > } > return nr_pinned; > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 2dc820e8c873..b32774f289d6 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1392,6 +1392,9 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma, > if (!pmd_write(*pmd) && gup_must_unshare(flags, page)) > return ERR_PTR(-EMLINK); > > + VM_BUG_ON((flags & FOLL_PIN) && PageAnon(page) && > + !PageAnonExclusive(page)); > + > if (!try_grab_page(page, flags)) > return ERR_PTR(-ENOMEM); > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 21f2ec446117..48740e6c3476 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -6097,6 +6097,9 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, > pfn_offset = (vaddr & ~huge_page_mask(h)) >> PAGE_SHIFT; > page = pte_page(huge_ptep_get(pte)); > > + VM_BUG_ON((flags & FOLL_PIN) && PageAnon(page) && > + !PageAnonExclusive(page)); > + > /* > * If subpage information not requested, update counters > * and skip the same_page loop below.