I do have x86 3 UML guest images, created at a x86 bit Gentoo Linux. Now I do have a 64 bit Gentoo Linux (hardened kernel == PAX + grsecurity) and tried to run such a guest. Often this attempt just gives an "write: File too large" : $ /home/tfoerste/workspace/bin/start_uml.sh -r trinity -l /usr/local/bin/linux-v3.18 Locating the bottom of the address space ... 0x1000 Locating the top of the address space ... 0xffffd000 Core dump limits : soft - 0 hard - NONE Checking that ptrace can change system call numbers...OK Checking syscall emulation patch for ptrace...OK Checking advanced syscall emulation patch for ptrace...OK Checking environment variables for a tempdir...none found Checking if /dev/shm is on tmpfs...OK Checking PROT_EXEC mmap in /dev/shm...OK Checking for the skas3 patch in the host: - /proc/mm...not found: No such file or directory - PTRACE_FAULTINFO...not found - PTRACE_LDT...not found UML running in SKAS0 mode Adding 51630080 bytes to physical memory to account for exec-shield gap write: File too large In mostly all other cases a 3.17 and 3.18 linux stops here : $ /home/tfoerste/workspace/bin/start_uml.sh -r trinity -l /usr/local/bin/linux-v3.18 Locating the bottom of the address space ... 0x1000 Locating the top of the address space ... 0xffffd000 Core dump limits : soft - 0 hard - NONE Checking that ptrace can change system call numbers...OK Checking syscall emulation patch for ptrace...OK Checking advanced syscall emulation patch for ptrace...OK Checking environment variables for a tempdir...none found Checking if /dev/shm is on tmpfs...OK Checking PROT_EXEC mmap in /dev/shm...OK Checking for the skas3 patch in the host: - /proc/mm...not found: No such file or directory - PTRACE_FAULTINFO...not found - PTRACE_LDT...not found UML running in SKAS0 mode Adding 45862912 bytes to physical memory to account for exec-shield gap Kernel virtual memory size shrunk to 1926234112 bytes bootconsole [earlycon0] enabled PID hash table entries: 4096 (order: 2, 16384 bytes) Dentry cache hash table entries: 262144 (order: 8, 1048576 bytes) Inode-cache hash table entries: 131072 (order: 7, 524288 bytes) Memory: 2022536K/2092788K available (4932K kernel code, 339K rwdata, 1808K rodata, 123K init, 241K bss, 70252K reserved) SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=1, Nodes=1 NR_IRQS:15 Calibrating delay loop... 5201.10 BogoMIPS (lpj=26005504) pid_max: default: 32768 minimum: 301 Mount-cache hash table entries: 4096 (order: 2, 16384 bytes) Mountpoint-cache hash table entries: 4096 (order: 2, 16384 bytes) Checking for host processor cmov support...Yes Checking that host ptys support output SIGIO...Yes Checking that host ptys support SIGIO on close...No, enabling workaround devtmpfs: initialized Using 2.6 host AIO xor: measuring software checksum speed 8regs : 10348.000 MB/sec 8regs_prefetch: 9242.400 MB/sec 32regs : 3920.000 MB/sec 32regs_prefetch: 3987.200 MB/sec xor: using function: 8regs (10348.000 MB/sec) prandom: seed boundary self test passed prandom: 100 self tests passed NET: Registered protocol family 16 raid6: int32x1 1360 MB/s raid6: int32x2 1303 MB/s raid6: int32x4 1201 MB/s raid6: int32x8 1005 MB/s raid6: using algorithm int32x1 (1360 MB/s) raid6: using intx1 recovery algorithm Switched to clocksource itimer NET: Registered protocol family 2 TCP established hash table entries: 16384 (order: 4, 65536 bytes) TCP bind hash table entries: 16384 (order: 6, 327680 bytes) TCP: Hash tables configured (established 16384 bind 16384) TCP: reno registered UDP hash table entries: 1024 (order: 3, 49152 bytes) UDP-Lite hash table entries: 1024 (order: 3, 49152 bytes) NET: Registered protocol family 1 RPC: Registered named UNIX socket transport module. RPC: Registered udp transport module. RPC: Registered tcp transport module. RPC: Registered tcp NFSv4.1 backchannel transport module. console [stderr0] disabled mconsole (version 2) initialized on /home/tfoerste/.uml/uml_trinity/mconsole Checking host MADV_REMOVE support...OK UML Audio Relay (host dsp = /dev/sound/dsp, host mixer = /dev/sound/mixer) Host TLS support detected Detected host type: x86_64 (GDT indexes 12 to 15) futex hash table entries: 256 (order: 0, 7168 bytes) audit: initializing netlink subsys (disabled) audit: type=2000 audit(1419844427.090:1): initialized zpool: loaded zbud: loaded NFS: Registering the id_resolver key type Key type id_resolver registered Key type id_legacy registered nfs4filelayout_init: NFSv4 File Layout Driver Registering... Installing knfsd (copyright (C) 1996 okir@monad.swb.de). msgmni has been set to 3950 alg: No test for stdrng (krng) Block layer SCSI generic (bsg) driver version 0.4 loaded (major 254) io scheduler noop registered (default) loop: module loaded device-mapper: uevent: version 1.0.3 device-mapper: ioctl: 4.28.0-ioctl (2014-09-17) initialised: dm-devel@redhat.com TCP: cubic registered NET: Registered protocol family 10 sit: IPv6 over IPv4 tunneling driver NET: Registered protocol family 17 Key type dns_resolver registered Initialized stdio console driver Console initialized on /dev/tty0 console [tty0] enabled console [tty0] enabled bootconsole [earlycon0] disabled bootconsole [earlycon0] disabled Initializing software serial port version 1 console [mc-1] enabled ubda: unknown partition table ubdb: unknown partition table Netdevice 0 (72:ef:3d:9f:c3:5a) : TUN/TAP backend - Btrfs loaded winch_thread : TIOCSCTTY failed on fd 1 err = 1 EXT4-fs (ubda): mounted filesystem with ordered data mode. Opts: (null) VFS: Mounted root (ext4 filesystem) readonly on device 98:0. devtmpfs: mounted With gdb I can see this : $ pgrep linux | xargs -n1 -i{} sudo gdb /home/tfoerste/devel/linux/linux {} -n -batch -ex 'bt' warning: Cannot call inferior functions, Linux kernel PaX protection forbids return to non-executable pages! 0xf2dc7ca0 in ?? () #0 0xf2dc7ca0 in ?? () #1 0x080636aa in init_new_context (task=0x868a0000, mm=0x3cc3) at arch/um/kernel/skas/mmu.c:68 #2 0x0807cf2c in unshare_fd (unshare_flags=4294966784, new_fdp=0x40000002) at kernel/fork.c:1840 #3 0x0807d200 in mm_free_pgd (mm=) at kernel/fork.c:503 #4 __mmdrop (mm=0x86398218) at kernel/fork.c:633 #5 0x08118399 in pipe_read (iocb=0xfffffe00, to=0x8718260 <_rs.48115>) at fs/pipe.c:312 #6 0x0805f1fb in run_init_process (init_filename=0xfffffe00 ) at init/main.c:910 #7 0x0805f20f in try_to_run_init_process (init_filename=0x85dce1c "/sbin/init") at init/main.c:919 #8 0x0851a052 in __list_del (next=, prev=) at include/linux/list.h:88 #9 __mutex_lock_common (subclass=, nest_lock=, ip=, use_ww_ctx=, ww_ctx=, state=, lock=) at kernel/locking/mutex.c:571 #10 __ww_mutex_lock_interruptible_slowpath (lock=0x0, ctx=0x0) at kernel/locking/mutex.c:807 #11 0x0806074b in new_thread_handler () at arch/um/kernel/process.c:129 #12 0x00000000 in ?? () warning: process 15547 is a cloned process ... Kernel 3.19-rc1-x is special : Host TLS support detected Detected host type: x86_64 (GDT indexes 12 to 15) futex hash table entries: 256 (order: 0, 7168 bytes) EIP: 0023:[<084d98d6>] CPU: 0 Not tainted ESP: 002b:858afe90 EFLAGS: 00010246 Not tainted EAX: 00000000 EBX: 0804ef22 ECX: 00000001 EDX: 858aff08 ESI: 00000000 EDI: 858afec8 EBP: 858afeac DS: 002b ES: 002b Kernel panic - not syncing: Segfault with no mm CPU: 0 PID: 1 Comm: swapper Not tainted 3.19.0-rc1-00058-g29169f8 #2 Stack: 00000004 08064e4f 858afec8 00000000 00000004 858afeb4 0804ef22 858afed8 080bd9ac 858afec8 00000000 00000004 00000000 00000000 00000000 0804ef22 08705064 85a42540 858aff10 0804efa5 00000000 0000001c 00000100 00000000 Call Trace: [<08064e4f>] ? copy_from_user+0x2f/0xa0 [<0804ef22>] ? futex_init+0x0/0xda [<080bd9ac>] cmpxchg_futex_value_locked+0x4c/0x100 [<0804ef22>] ? futex_init+0x0/0xda [<0804efa5>] futex_init+0x83/0xda [<0804ef22>] ? futex_init+0x0/0xda [<08048abc>] do_one_initcall+0x12b/0x1dd [<0804ef22>] ? futex_init+0x0/0xda [<08075318>] ? set_signals+0x38/0x50 [<08074ffa>] ? unblock_signals+0x1a/0x90 [<08048239>] ? repair_env_string+0x1a/0x91 [<08097905>] ? parse_args+0x335/0x4d0 [<08048c67>] kernel_init_freeable+0xf9/0x19d [<08048c67>] ? kernel_init_freeable+0xf9/0x19d [<0804ef22>] ? futex_init+0x0/0xda [<0804821f>] ? repair_env_string+0x0/0x91 [<0852351b>] kernel_init+0xb/0xe0 [<0806174b>] new_thread_handler+0x6b/0x90 /home/tfoerste/workspace/bin/start_uml.sh: line 108: 15791 Aborted $LINUX earlyprintk ubda=$ROOTFS ubdb=$SWAP eth0=$NET mem=$MEM $TTY umid=uml_$NAME rootfstype=ext4 "$ARGS" The .config is attached. -- Toralf pgp key: 7B1A 07F4 EC82 0F90 D4C2 8936 872A E508 0076 E94E