Messages in this thread | | | From | "Sebastian Herbszt" <> | Subject | Re: Boot failures on Qemu due to P6_NOPS | Date | Mon, 7 Jul 2008 19:55:43 +0200 |
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Christian Ehrhardt wrote:
> Hi, > > this might well be a bug in Qemu but even then, it would be nice if the > linux kernel could do a work around. > > I tried to boot a current git kernel (around 2.6.26-rc8) on qemu and > got the an invalid opcode oops on boot (full oops data below). > > The illegal instruction is 0x0f 0x1f 0x00 aka P6_NOP3. > > I have verified that this opcode gets patched in because > apply_alternatives() or more precisely add_nops() uses P6 nops > on this CPU type while padding after patching in an fxsave > instruction. More precisely the code that oopses is: > > fxsave (%eax) > btl $0x7,0x2(%eax) > jae 0x804833e <main+26> > fnclex > nopl (%eax) <==== Faulting instruction > > P6 nops are used when patching because init_intel() sets X86_FEATURE_P3 for > family 6 CPUs and X86_FEATURE_P3 in turn enables the P6 NOPS. > > The Qemu CPU identifies itself as follows: > > processor : 0 > vendor_id : GenuineIntel > cpu family : 6 > model : 3 > model name : Pentium II (Klamath) > stepping : 3 > cpu MHz : 1862.133 > > I have no idea if this specific CPU type should support this specific > instruction. If it really should this is obviously a Qemu bug but it > might be reasonable to work around this in the linux kernel. > > The kernel is configured with CONFIG_M586 but without CONFIG_X86_GENERIC > (full config upon request). Apparently setting CONFIG_X86_GENERIC works > around the problem. > > ========== ooops data follows =================================== > invalid opcode: 0000 [#1] SMP > Modules linked in: > > Pid: 0, comm: swapper Not tainted (2.6.26-rc9 #1) > EIP: 0060:[<c0102035>] EFLAGS: 00000202 CPU: 0 > EIP is at prepare_to_copy+0x1d/0x43 > EAX: c781de00 EBX: 00000000 ECX: c03f3f9c EDX: c03c23e0 > ESI: fffffff4 EDI: c03c23e0 EBP: 00000000 ESP: c03f3f08 > DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 > Process swapper (pid: 0, ti=c03f2000 task=c03c23e0 task.ti=c03f2000) > Stack: c011c653 c03f3f9c 00000000 00800b00 00000286 00000000 00000000 00000000 > 00800b00 c03f3f9c 00000000 c011d671 00000000 00000000 00000000 00000000 > c03c8cb0 00000246 c03c8a80 00000046 00000000 00000002 00000001 c014a30c > Call Trace: > [<c011c653>] copy_process+0x70/0xf75 > [<c011d671>] do_fork+0xab/0x19c > [<c014a30c>] free_pages_bulk+0x23/0x1d0 > [<c0108b4a>] native_sched_clock+0x90/0xa4 > [<c03f72fd>] kernel_init+0x0/0x25d > [<c01024b1>] kernel_thread+0x78/0x80 > [<c03f72fd>] kernel_init+0x0/0x25d > [<c0104af0>] kernel_thread_helper+0x0/0x10 > [<c02e0d39>] rest_init+0x11/0x4b > [<c03f7811>] start_kernel+0x2a0/0x2a3 > ======================= > Code: ff 05 0c 20 47 c0 c3 ff 0d 0c 20 47 c0 c3 89 c2 8b 40 04 f6 40 0c > 01 74 30 8b 82 6c 02 00 00 0f ae 00 0f ba 60 02 07 73 02 db e2 <0f> 1f > 00 90 8d b4 26 00 00 00 00 89 f6 8b 42 04 83 60 0c fe 0f > EIP: [<c0102035>] prepare_to_copy+0x1d/0x43 SS:ESP 0068:c03f3f08 > ---[ end trace 4eaa2a86a8e2da22 ]--- > Kernel panic - not syncing: Attempted to kill the idle task! >
This is a problem in old qemu versions which don't support multi byte NOPs. Please check previous discussion about it at http://lkml.org/lkml/2008/5/3/60.
- Sebastian
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