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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D7CF4C433EF for ; Mon, 4 Oct 2021 16:54:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AF6D7613DB for ; Mon, 4 Oct 2021 16:54:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237668AbhJDQ4X (ORCPT ); Mon, 4 Oct 2021 12:56:23 -0400 Received: from mail.kernel.org ([198.145.29.99]:57784 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237646AbhJDQ4V (ORCPT ); Mon, 4 Oct 2021 12:56:21 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 9F74161381; Mon, 4 Oct 2021 16:54:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1633366472; bh=TvvpjQdHQdhLT/lXbu5+Haobdd8e9Zwi1ru4E+zI7wI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=QQZNB2sOslZIecnGF+eD4IyTpxYTRbfRMbD/U+SeJqOti2xoV+DA9fdiH85bcAKH8 csiv9beEQIu/f491XDdtQY997mWjReJ+R3fljw63ThoJv9akyTW8La2NTc6DBr73RM 2HxaJBPuMr6CohDFSI82HV+kLgfqz/WEoiQHcC/4JRFmgt5CBh9Q4fUuPmI41IIwzI /cYLvWNP8ONCt7I6nuip/mx4BNtptQN8LC6REzXgRcG0Jhvt+pp3hz2qU+1/C3mW/Q E00wf2b8E+hgVsreo78g1LWRXUm3Z2VOd+7cH2K2mhAWCzfd+CpyolrB+nr9r4Hg18 eQTfUVg0BSBuA== Date: Mon, 4 Oct 2021 09:54:32 -0700 From: "Darrick J. Wong" To: Sean Christopherson Cc: Stephen , kvm@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: kvm crash in 5.14.1? Message-ID: <20211004165432.GA24266@magnolia> References: <2b5ca6d3-fa7b-5e2f-c353-f07dcff993c1@gmail.com> <16c7a433-6e58-4213-bc00-5f6196fe22f5@gmail.com> <20210930175957.GA10573@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20210930175957.GA10573@magnolia> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Sep 30, 2021 at 10:59:57AM -0700, Darrick J. Wong wrote: > On Wed, Sep 29, 2021 at 03:21:09PM +0000, Sean Christopherson wrote: > > On Tue, Sep 28, 2021, Stephen wrote: > > > Hello, > > > > > > I got this crash again on 5.14.7 in the early morning of the 27th. > > > Things hung up shortly after I'd gone to bed. Uptime was 1 day 9 hours 9 > > > minutes. > > > > ... > > > > > BUG: kernel NULL pointer dereference, address: 0000000000000068 > > > #PF: supervisor read access in kernel mode > > > #PF: error_code(0x0000) - not-present page > > > PGD 0 P4D 0 > > > Oops: 0000 [#1] SMP NOPTI > > > CPU: 21 PID: 8494 Comm: CPU 7/KVM Tainted: G            E     5.14.7 #32 > > > Hardware name: Gigabyte Technology Co., Ltd. X570 AORUS ELITE WIFI/X570 > > > AORUS ELITE WIFI, BIOS F35 07/08/2021 > > > RIP: 0010:internal_get_user_pages_fast+0x738/0xda0 > > > Code: 84 24 a0 00 00 00 65 48 2b 04 25 28 00 00 00 0f 85 54 06 00 00 48 > > > 81 c4 a8 00 00 00 44 89 e0 5b 5d 41 5c 41 5d 41 5e 41 5f c3 <48> 81 78 > > > 68 a0 a3 > > > > > I haven't reproduced the crash, but the code signature (CMP against an absolute > > address) is quite distinct, and is consistent across all three crashes. I'm pretty > > sure the issue is that page_is_secretmem() doesn't check for a null page->mapping, > > e.g. if the page is truncated, which IIUC can happen in parallel since gup() doesn't > > hold the lock. > > > > I think this should fix the problems? > > > > diff --git a/include/linux/secretmem.h b/include/linux/secretmem.h > > index 21c3771e6a56..988528b5da43 100644 > > --- a/include/linux/secretmem.h > > +++ b/include/linux/secretmem.h > > @@ -23,7 +23,7 @@ static inline bool page_is_secretmem(struct page *page) > > mapping = (struct address_space *) > > ((unsigned long)page->mapping & ~PAGE_MAPPING_FLAGS); > > > > - if (mapping != page->mapping) > > + if (!mapping || mapping != page->mapping) > > I'll roll this out on my vm host and try to re-run the mass fuzztest > overnight, though IT claims they're going to kill power to the whole > datacenter until Monday(!)... ...which they did, 30 minutes after I sent this email. :( I'll hopefully be able to report back to the list in a day or two. --D > > --D > > > return false; > > > > return mapping->a_ops == &secretmem_aops;