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 c03f3f9...
