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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20191209211502.zhbvzv2qwbvcperm@ca-dmjordan1.us.oracle.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-MC-Unique: laAmNaQoMZGmiLgtL7GHyQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09.12.19 22:15, Daniel Jordan wrote: > Hi David, >=20 > On Mon, Dec 09, 2019 at 06:48:34PM +0100, David Hildenbrand wrote: >> If max_pfn is not aligned to a section boundary, we can easily run into >> BUGs. This can e.g., be triggered on x86-64 under QEMU by specifying a >> memory size that is not a multiple of 128MB (e.g., 4097MB, but also >> 4160MB). I was told that on real HW, we can easily have this scenario >> (esp., one of the main reasons sub-section hotadd of devmem was added). >> >> The issue is, that we have a valid memmap (pfn_valid()) for the >> whole section, and the whole section will be marked "online". >> pfn_to_online_page() will succeed, but the memmap contains garbage. >> >> E.g., doing a "cat /proc/kpageflags > /dev/null" results in >> >> [ 303.218313] BUG: unable to handle page fault for address: fffffffffff= ffffe >> [ 303.218899] #PF: supervisor read access in kernel mode >> [ 303.219344] #PF: error_code(0x0000) - not-present page >> [ 303.219787] PGD 12614067 P4D 12614067 PUD 12616067 PMD 0 >> [ 303.220266] Oops: 0000 [#1] SMP NOPTI >> [ 303.220587] CPU: 0 PID: 424 Comm: cat Not tainted 5.4.0-next-20191128= + #17 >=20 Hi Daniel, > I can't reproduce this on x86-64 qemu, next-20191128 or mainline, with ei= ther > memory size. What config are you using? How often are you hitting it? Thanks for verifying! Hah, there is one piece missing to reproduce via "cat /proc/kpageflags > /dev/null" that I ignored on my QEMU cmdline (see b= elow) I can reproduce it reliably (QEMU with "-m 4160M") via [root@localhost ~]# uname -a Linux localhost 5.5.0-rc1-next-20191209 #93 SMP Tue Dec 10 10:46:19 CET 201= 9 x86_64 x86_64 x86_64 GNU/Linux [root@localhost ~]# ./page-types -r -a 0x144001 [ 200.476376] BUG: unable to handle page fault for address: ffffffffffffff= fe [ 200.477500] #PF: supervisor read access in kernel mode [ 200.478334] #PF: error_code(0x0000) - not-present page [ 200.479076] PGD 59614067 P4D 59614067 PUD 59616067 PMD 0=20 [ 200.479557] Oops: 0000 [#4] SMP NOPTI [ 200.479875] CPU: 0 PID: 603 Comm: page-types Tainted: G D W = 5.5.0-rc1-next-20191209 #93 [ 200.480646] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS = rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu4 [ 200.481648] RIP: 0010:stable_page_flags+0x4d/0x410 [ 200.482061] Code: f3 ff 41 89 c0 48 b8 00 00 00 00 01 00 00 00 45 84 c0 = 0f 85 cd 02 00 00 48 8b 53 08 48 8b 2b 48f [ 200.483644] RSP: 0018:ffffb139401cbe60 EFLAGS: 00010202 [ 200.484091] RAX: fffffffffffffffe RBX: fffffbeec5100040 RCX: 00000000000= 00000 [ 200.484697] RDX: 0000000000000001 RSI: ffffffff9535c7cd RDI: 00000000000= 00246 [ 200.485313] RBP: ffffffffffffffff R08: 0000000000000000 R09: 00000000000= 00000 [ 200.485917] R10: 0000000000000000 R11: 0000000000000000 R12: 00000000001= 44001 [ 200.486523] R13: 00007ffd6ba55f48 R14: 00007ffd6ba55f40 R15: ffffb139401= cbf08 [ 200.487130] FS: 00007f68df717580(0000) GS:ffff9ec77fa00000(0000) knlGS:= 0000000000000000 [ 200.487804] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 200.488295] CR2: fffffffffffffffe CR3: 0000000135d48000 CR4: 00000000000= 006f0 [ 200.488897] Call Trace: [ 200.489115] kpageflags_read+0xe9/0x140 [ 200.489447] proc_reg_read+0x3c/0x60 [ 200.489755] vfs_read+0xc2/0x170 [ 200.490037] ksys_pread64+0x65/0xa0 [ 200.490352] do_syscall_64+0x5c/0xa0 [ 200.490665] entry_SYSCALL_64_after_hwframe+0x49/0xbe (tool located in tools/vm/page-types.c, see also patch #2) To reproduce via "cat /proc/kpageflags > /dev/null", you have to hot/coldplug one DIMM, to move max_pfn beyond the garbage memmap (see also patch #2). My QEMU cmdline with Fedora 31: qemu-system-x86_64 \ --enable-kvm \ -m 4160M,slots=3D4,maxmem=3D8G \ -hda Fedora-Cloud-Base-31-1.9.x86_64.qcow2 \ -machine pc \ -nographic \ -nodefaults \ -chardev stdio,id=3Dserial,signal=3Doff \ -device isa-serial,chardev=3Dserial \ -object memory-backend-ram,id=3Dmem0,size=3D1024M \ -device pc-dimm,id=3Ddimm0,memdev=3Dmem0 [root@localhost ~]# uname -a Linux localhost 5.3.7-301.fc31.x86_64 #1 SMP Mon Oct 21 19:18:58 UTC 2019 x= 86_64 x86_64 x86_64 GNU/Linux [root@localhost ~]# cat /proc/kpageflags > /dev/null [ 111.517275] BUG: unable to handle page fault for address: ffffffffffffff= fe [ 111.517907] #PF: supervisor read access in kernel mode [ 111.518333] #PF: error_code(0x0000) - not-present page [ 111.518771] PGD a240e067 P4D a240e067 PUD a2410067 PMD 0=20 >=20 > It may not have anything to do with the config, and I may be getting luck= y with > the garbage in my memory. >=20 Some things that might be relevant from my config. # CONFIG_PAGE_POISONING is not set CONFIG_DEFERRED_STRUCT_PAGE_INIT=3Dy CONFIG_SPARSEMEM_EXTREME=3Dy CONFIG_SPARSEMEM_VMEMMAP_ENABLE=3Dy CONFIG_SPARSEMEM_VMEMMAP=3Dy CONFIG_HAVE_MEMBLOCK_NODE_MAP=3Dy CONFIG_MEMORY_HOTPLUG=3Dy CONFIG_MEMORY_HOTPLUG_SPARSE=3Dy CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE=3Dy The F31 default config should make it trigger. Will update this patch description - thanks! ... --=20 Thanks, David / dhildenb