From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f199.google.com (mail-pf0-f199.google.com [209.85.192.199]) by kanga.kvack.org (Postfix) with ESMTP id 335F76B0010 for ; Fri, 20 Apr 2018 11:42:35 -0400 (EDT) Received: by mail-pf0-f199.google.com with SMTP id f19so4841944pfn.6 for ; Fri, 20 Apr 2018 08:42:35 -0700 (PDT) Received: from prv1-mh.provo.novell.com (prv1-mh.provo.novell.com. [137.65.248.33]) by mx.google.com with ESMTPS id 60-v6si5781360plc.453.2018.04.20.08.42.33 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 20 Apr 2018 08:42:34 -0700 (PDT) Message-Id: <5ADA0A6D02000078001BD177@prv1-mh.provo.novell.com> Date: Fri, 20 Apr 2018 09:42:37 -0600 From: "Jan Beulich" Subject: Re: [Xen-devel] [Bug 198497] handle_mm_fault / xen_pmd_val / radix_tree_lookup_slot Null pointer References: <20180420133951.GC10788@bombadil.infradead.org> <76a4ee3b-e00a-5032-df90-07d8e207f707@citrix.com> In-Reply-To: <76a4ee3b-e00a-5032-df90-07d8e207f707@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Cooper Cc: bugzilla-daemon@bugzilla.kernel.org, Jason Andryuk , Matthew Wilcox , linux-mm@kvack.org, akpm@linux-foundation.org, xen-devel@lists.xen.org, Boris Ostrovsky , labbott@redhat.com, Juergen Gross >>> On 20.04.18 at 17:25, wrote: > On 20/04/18 16:20, Jason Andryuk wrote: >> Adding xen-devel and the Linux Xen maintainers. >> >> Summary: Some Xen users (and maybe others) are hitting a BUG in >> __radix_tree_lookup() under do_swap_page() - example backtrace is >> provided at the end. Matthew Wilcox provided a band-aid patch that >> prints errors like the following instead of triggering the bug. >> >> Skylake 32bit PAE Dom0: >> Bad swp_entry: 80000000 >> mm/swap_state.c:683: bad pte d3a39f1c(8000000400000000) >> >> Ivy Bridge 32bit PAE Dom0: >> Bad swp_entry: 40000000 >> mm/swap_state.c:683: bad pte d3a05f1c(8000000200000000) >> >> Other 32bit DomU: >> Bad swp_entry: 4000000 >> mm/swap_state.c:683: bad pte e2187f30(8000000200000000) >> >> Other 32bit: >> Bad swp_entry: 2000000 >> mm/swap_state.c:683: bad pte ef3a3f38(8000000100000000) >> >> The Linux bugzilla has more info >> https://bugzilla.kernel.org/show_bug.cgi?id=3D198497=20 >> >> This may not be exclusive to Xen Linux, but most of the reports are on >> Xen. Matthew wonders if Xen might be stepping on the upper bits of a >> pte. >=20 > Yes - Xen does use the upper bits of a PTE, but only 1 in release > builds, and a second in debug builds. I don't understand where you're > getting the 3rd bit in there. The former supposedly is _PAGE_GUEST_KERNEL, which we use for 64-bit guests only. Above talk is of 32-bit guests only. In addition both this and _PAGE_GNTTAB are used on present PTEs only, while above talk is about swap entries. Jan