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 E745EC77B71 for ; Wed, 12 Apr 2023 08:52:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231381AbjDLIwm (ORCPT ); Wed, 12 Apr 2023 04:52:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40894 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231452AbjDLIwe (ORCPT ); Wed, 12 Apr 2023 04:52:34 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CF61583D8 for ; Wed, 12 Apr 2023 01:52:15 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 75983630E4 for ; Wed, 12 Apr 2023 08:46:35 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 85955C4339B; Wed, 12 Apr 2023 08:46:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1681289194; bh=Z+ZBg97YQPZ8DZ+RHaYqeucicUfB0Tyc/gqv88F12Qk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=PSb+q/jLcYA1OuvA/B2J6DardLc6Ws2y2u+uB+xxPGG9Wol9cxsyNmjSsWlP6HrUZ 5m5lDvy2kEHCkv5/8fSXE8xlJGPCXWx8SVRcERAH3twCxydpnu9Kg81ZP81ynVV48I mrrVq2sRAVQtcSs8pQmxZ8rZxyv9cev/sEhwomXg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Alistair Popple , Ralph Campbell , John Hubbard , David Hildenbrand , "Matthew Wilcox (Oracle)" , Christoph Hellwig , Andrew Morton Subject: [PATCH 6.1 151/164] mm: take a page reference when removing device exclusive entries Date: Wed, 12 Apr 2023 10:34:33 +0200 Message-Id: <20230412082843.051890441@linuxfoundation.org> X-Mailer: git-send-email 2.40.0 In-Reply-To: <20230412082836.695875037@linuxfoundation.org> References: <20230412082836.695875037@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Alistair Popple commit 7c7b962938ddda6a9cd095de557ee5250706ea88 upstream. Device exclusive page table entries are used to prevent CPU access to a page whilst it is being accessed from a device. Typically this is used to implement atomic operations when the underlying bus does not support atomic access. When a CPU thread encounters a device exclusive entry it locks the page and restores the original entry after calling mmu notifiers to signal drivers that exclusive access is no longer available. The device exclusive entry holds a reference to the page making it safe to access the struct page whilst the entry is present. However the fault handling code does not hold the PTL when taking the page lock. This means if there are multiple threads faulting concurrently on the device exclusive entry one will remove the entry whilst others will wait on the page lock without holding a reference. This can lead to threads locking or waiting on a folio with a zero refcount. Whilst mmap_lock prevents the pages getting freed via munmap() they may still be freed by a migration. This leads to warnings such as PAGE_FLAGS_CHECK_AT_FREE due to the page being locked when the refcount drops to zero. Fix this by trying to take a reference on the folio before locking it. The code already checks the PTE under the PTL and aborts if the entry is no longer there. It is also possible the folio has been unmapped, freed and re-allocated allowing a reference to be taken on an unrelated folio. This case is also detected by the PTE check and the folio is unlocked without further changes. Link: https://lkml.kernel.org/r/20230330012519.804116-1-apopple@nvidia.com Fixes: b756a3b5e7ea ("mm: device exclusive memory access") Signed-off-by: Alistair Popple Reviewed-by: Ralph Campbell Reviewed-by: John Hubbard Acked-by: David Hildenbrand Cc: Matthew Wilcox (Oracle) Cc: Christoph Hellwig Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/memory.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) --- a/mm/memory.c +++ b/mm/memory.c @@ -3619,8 +3619,21 @@ static vm_fault_t remove_device_exclusiv struct vm_area_struct *vma = vmf->vma; struct mmu_notifier_range range; - if (!folio_lock_or_retry(folio, vma->vm_mm, vmf->flags)) + /* + * We need a reference to lock the folio because we don't hold + * the PTL so a racing thread can remove the device-exclusive + * entry and unmap it. If the folio is free the entry must + * have been removed already. If it happens to have already + * been re-allocated after being freed all we do is lock and + * unlock it. + */ + if (!folio_try_get(folio)) + return 0; + + if (!folio_lock_or_retry(folio, vma->vm_mm, vmf->flags)) { + folio_put(folio); return VM_FAULT_RETRY; + } mmu_notifier_range_init_owner(&range, MMU_NOTIFY_EXCLUSIVE, 0, vma, vma->vm_mm, vmf->address & PAGE_MASK, (vmf->address & PAGE_MASK) + PAGE_SIZE, NULL); @@ -3633,6 +3646,7 @@ static vm_fault_t remove_device_exclusiv pte_unmap_unlock(vmf->pte, vmf->ptl); folio_unlock(folio); + folio_put(folio); mmu_notifier_invalidate_range_end(&range); return 0;