Only allocate the FPU area when the application actually uses FPU, i.e., in the
first lazy FPU trap. This could save memory for non-fpu using apps.

for example: on my system after boot, there are around 300 processes, with
only 17 using FPU.
Signed-off-by: NSuresh Siddha <suresh.b.siddha@intel.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

Split the FPU save area from the task struct. This allows easy migration
of FPU context, and it's generally cleaner. It also allows the following
two optimizations:

1) only allocate when the application actually uses FPU, so in the first
lazy FPU trap. This could save memory for non-fpu using apps. Next patch
does this lazy allocation.

2) allocate the right size for the actual cpu rather than 512 bytes always.
Patches enabling xsave/xrstor support (coming shortly) will take advantage
of this.
Signed-off-by: NSuresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: NArjan van de Ven <arjan@linux.intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

This annotates NMI functions with notrace. Some tracers may be able
to live with this, but some cannot. The safest is to turn it off,
it's not particularly interesting anyway.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

This patch fixes the hang regression with kgdb when the NMI interrupt
comes in while the master core is returning from an exception.

Adjust the NMI logic such that KGDB will not stop NMI exceptions from
occurring by in general returning NOTIFY_DONE.  It is not possible to
distinguish the debug NMI sync vs the normal NMI apic interrupt so
kgdb needs to catch the unknown NMI if it the debugger was previously
active on one of the cpus.
Signed-off-by: NJason Wessel <jason.wessel@windriver.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

This patch renames VM_MASK to X86_VM_MASK (which
in turn defined as alias to X86_EFLAGS_VM) to better
distinguish from virtual memory flags. We can't just
use X86_EFLAGS_VM instead because it is also used
for conditional compilation
Signed-off-by: NCyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

- fix build error
- fix CONFIG_HEADERS_CHECK error
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Before:
   total: 86 errors, 29 warnings, 1248 lines checked
After:
   total: 0 errors, 17 warnings, 1281 lines checked

No code changed:

arch/x86/kernel/traps_32.o:

   text	   data	    bss	    dec	    hex	filename
   8711	   2168	     72	  10951	   2ac7	traps_32.o.before
   8711	   2168	     72	  10951	   2ac7	traps_32.o.after

(md5 sums differ because some stack offset positions changed.)
Signed-off-by: NIngo Molnar <mingo@elte.hu>

This was being used to ensure the proper alignment of the FXSAVE/FXRSTOR data.
This would create a sparse error in the _correct_ cases, hiding further
warnings.  Use BUILD_BUG_ON instead.
Signed-off-by: NHarvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

Small fomatting fixes to 64-bit as well, trailing whitespace
and extra semicolon, also move the ifdefs for CONFIG_KALLSYMS
into the function itself.
Signed-off-by: NHarvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

They now look like:

hal-resmgr[13791]: segfault at 3c rip 2b9c8caec182 rsp 7fff1e825d30 error 4 in libacl.so.1.1.0[2b9c8caea000+6000]

This makes it easier to pinpoint bugs to specific libraries.

And printing the offset into a mapping also always allows to find the
correct fault point in a library even with randomized mappings. Previously
there was no way to actually find the correct code address inside
the randomized mapping.

Relies on earlier patch to shorten the printk formats.

They are often now longer than 80 characters, but I think that's worth it.

[includes fix from Eric Dumazet to check d_path error value]
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

Right now, we take the stack pointer early during the backtrace path, but
only calculate bp several functions deep later, making it hard to reconcile
the stack and bp backtraces (as well as showing several internal backtrace
functions on the stack with bp based backtracing).

This patch moves the bp taking to the same place we take the stack pointer;
sadly this ripples through several layers of the back tracing stack,
but it's not all that bad in the end I hope.
Signed-off-by: NArjan van de Ven <arjan@linux.intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

The 32 bit Frame Pointer backtracer code checks if the EBP is valid
to do a backtrace; however currently on a failure it just gives up
and prints nothing. That's not very nice; we can do better and still
print a decent backtrace.

This patch changes the backtracer to use the regular backtracing algorithm
at the same time as the EBP backtracer; the EBP backtracer is basically
used to figure out which part of the backtrace are reliable vs those
which are likely to be noise.
Signed-off-by: NArjan van de Ven <arjan@linux.intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

For enhancing the 32 bit EBP based backtracer, I need the capability
for the backtracer to tell it's customer that an entry is either
reliable or unreliable, and the backtrace printing code then needs to
print the unreliable ones slightly different.

This patch adds the basic capability, the next patch will add a user
of this capability.
Signed-off-by: NArjan van de Ven <arjan@linux.intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

The current x86 32 bit FRAME_POINTER chasing code has a nasty bug in
that the EBP tracer doesn't actually update the value of EBP it is
tracing, so that the code doesn't actually switch to the irq stack
properly.

The result is a truncated backtrace:

 WARNING: at timeroops.c:8 kerneloops_regression_test() (Not tainted)
 Pid: 0, comm: swapper Not tainted 2.6.24-0.77.rc4.git4.fc9 #1
  [<c040649a>] show_trace_log_lvl+0x1a/0x2f
  [<c0406d41>] show_trace+0x12/0x14
  [<c0407061>] dump_stack+0x6c/0x72
  [<e0258049>] kerneloops_regression_test+0x44/0x46 [timeroops]
  [<c04371ac>] run_timer_softirq+0x127/0x18f
  [<c0434685>] __do_softirq+0x78/0xff
  [<c0407759>] do_softirq+0x74/0xf7
  =======================

This patch fixes the code to update EBP properly, and to check the EIP
before printing (as the non-framepointer backtracer does) so that
the same test backtrace now looks like this:

 WARNING: at timeroops.c:8 kerneloops_regression_test()
 Pid: 0, comm: swapper Not tainted 2.6.24-rc7 #4
  [<c0405d17>] show_trace_log_lvl+0x1a/0x2f
  [<c0406681>] show_trace+0x12/0x14
  [<c0406ef2>] dump_stack+0x6a/0x70
  [<e01f6040>] kerneloops_regression_test+0x3b/0x3d [timeroops]
  [<c0426f07>] run_timer_softirq+0x11b/0x17c
  [<c04243ac>] __do_softirq+0x42/0x94
  [<c040704c>] do_softirq+0x50/0xb6
  [<c04242a9>] irq_exit+0x37/0x67
  [<c040714c>] do_IRQ+0x9a/0xaf
  [<c04057da>] common_interrupt+0x2e/0x34
  [<c05807fe>] cpuidle_idle_call+0x52/0x78
  [<c04034f3>] cpu_idle+0x46/0x60
  [<c05fbbd3>] rest_init+0x43/0x45
  [<c070aa3d>] start_kernel+0x279/0x27f
  =======================

This shows that the backtrace goes all the way down to user context now.
This bug was found during the port to 64 bit of the frame pointer backtracer.
Signed-off-by: NArjan van de Ven <arjan@linux.intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

Small step towards unifying traps_32|64.c.  No functional
changes.  Pull out a small helper from an if() statement
in die().

Marked as __kprobes as eventually we will want to call this
from do_page_fault similar to how X86_64 does it.
Signed-off-by: NHarvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

fastcall is always defined to be empty, remove it from arch/x86
Signed-off-by: NHarvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

This patch moves _set_gate and its users to desc.h. We can now
use common code for x86_64 and i386.

[ mingo@elte.hu: set_system_gate() fixes for nasty crashes. ]
Signed-off-by: NGlauber de Oliveira Costa <gcosta@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

To account for the differences in gate descriptor in i386 and x86_64
a gate_desc type is introduced.
Signed-off-by: NGlauber de Oliveira Costa <gcosta@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

This patch aims to make the access of struct desc_struct variables
equal across architectures. In this patch, I unify the i386 and x86_64
versions under an anonymous union, keeping the way they are accessed
untouched (a and b for 32-bit code, individual bit-fields for 64-bit).

This solution is not beautiful, but will allow us to integrate common
code that differed by the way descriptors were used. This is to be viewed
incrementally. There's simply too much code to be fixed at once.

In the future, goal is to set up in a single way of acessing
the desc_struct fields.
Signed-off-by: NGlauber de Oliveira Costa <gcosta@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

This changes size-specific register names (eip/rip, esp/rsp, etc.) to
generic names in the thread and tss structures.
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

This replaces the debugreg[7] member of thread_struct with individual
members debugreg0, etc.  This saves two words for the dummies 4 and 5,
and harmonizes the code between 32 and 64.
Signed-off-by: NRoland McGrath <roland@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

We have a lot of code which differs only by the naming of specific
members of structures that contain registers.  In order to enable
additional unifications, this patch drops the e- or r- size prefix
from the register names in struct pt_regs, and drops the x- prefixes
for segment registers on the 32-bit side.

This patch also performs the equivalent renames in some additional
places that might be candidates for unification in the future.
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

This implements user-mode step-until-branch on x86 using the BTF bit
in MSR_IA32_DEBUGCTLMSR.  It's just like single-step, only less so.
Signed-off-by: NRoland McGrath <roland@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

On Sat, 2007-12-29 at 18:06 +0100, Marcin Slusarz wrote:
> Hi
> Today I've got this (while i was upgrading my gentoo box):
>
> WARNING: at kernel/lockdep.c:2658 check_flags()
> Pid: 21680, comm: conftest Not tainted 2.6.24-rc6 #63
>
> Call Trace:
>  [<ffffffff80253457>] check_flags+0x1c7/0x1d0
>  [<ffffffff80257217>] lock_acquire+0x57/0xc0
>  [<ffffffff8024d5c0>] __atomic_notifier_call_chain+0x60/0xd0
>  [<ffffffff8024d641>] atomic_notifier_call_chain+0x11/0x20
>  [<ffffffff8024d67e>] notify_die+0x2e/0x30
>  [<ffffffff8020da0a>] do_divide_error+0x5a/0xa0
>  [<ffffffff80522bdd>] trace_hardirqs_on_thunk+0x35/0x3a
>  [<ffffffff80255b89>] trace_hardirqs_on+0xd9/0x180
>  [<ffffffff80522bdd>] trace_hardirqs_on_thunk+0x35/0x3a
>  [<ffffffff80523c2d>] error_exit+0x0/0xa9
>
> possible reason: unannotated irqs-off.
> irq event stamp: 4693
> hardirqs last  enabled at (4693): [<ffffffff80522bdd>] trace_hardirqs_on_thunk+0x35/0x3a
> hardirqs last disabled at (4692): [<ffffffff80522c17>] trace_hardirqs_off_thunk+0x35/0x37
> softirqs last  enabled at (3546): [<ffffffff80238343>] __do_softirq+0xb3/0xd0
> softirqs last disabled at (3521): [<ffffffff8020c97c>] call_softirq+0x1c/0x30

more early fixups for notify_die()..
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Andrew "Eagle Eye" Morton noticed that we use raw_local_save_flags()
instead of raw_local_irq_save(flags) in die(). This allows the
preemption of oopsing contexts - which is highly undesirable. It also
causes CONFIG_DEBUG_PREEMPT to complain, as reported by Miles Lane.

this bug was introduced via:

  commit 39743c9e
  Author: Andi Kleen <ak@suse.de>
  Date:   Fri Oct 19 20:35:03 2007 +0200

      x86: use raw locks during oopses

-               spin_lock_irqsave(&die.lock, flags);
+               __raw_spin_lock(&die.lock);
+               raw_local_save_flags(flags);

that is not a correct open-coding of spin_lock_irqsave(): both the
ordering is wrong (irqs should be disabled _first_), and the wrong
flags-saving API was used.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Ensure the hardirq state is consistent before using locks. Use the rare
trace_hardirqs_fixup() because the trap can happen in any context.

resolves this rare lockdep warning:

WARNING: at kernel/lockdep.c:2658 check_flags()
 [<c013571e>] check_flags+0x90/0x140
 [<c0138a69>] lock_release+0x4b/0x1d0
 [<c0507fea>] notifier_call_chain+0x2a/0x47
 [<c050806b>] __atomic_notifier_call_chain+0x64/0x6d
 [<c0508007>] __atomic_notifier_call_chain+0x0/0x6d
 [<c050808b>] atomic_notifier_call_chain+0x17/0x1a
 [<c0131802>] notify_die+0x30/0x34
 [<c0506b09>] do_debug+0x3e/0xd4
 [<c050658f>] debug_stack_correct+0x27/0x2c
 [<c04be389>] tcp_rcv_established+0x1/0x620
 [<c04c38c2>] tcp_v4_do_rcv+0x2b/0x313
 [<c04c56b6>] tcp_v4_rcv+0x467/0x85d
 [<c0505ff2>] _spin_lock_nested+0x27/0x32
 [<c04c5a4d>] tcp_v4_rcv+0x7fe/0x85d
 [<c04c560e>] tcp_v4_rcv+0x3bf/0x85d
 [<c04adbb5>] ip_local_deliver_finish+0x11b/0x1b0
 [<c04adac8>] ip_local_deliver_finish+0x2e/0x1b0
 [<c04ada7b>] ip_rcv_finish+0x27b/0x29a
 [<c04961e5>] netif_receive_skb+0xfb/0x2a6
 [<c04add0f>] ip_rcv+0x0/0x1fb
 [<c0496354>] netif_receive_skb+0x26a/0x2a6
 [<c04961e5>] netif_receive_skb+0xfb/0x2a6
 [<c049872e>] process_backlog+0x7f/0xc6
 [<c04983ba>] net_rx_action+0xb9/0x1ac
 [<c0498348>] net_rx_action+0x47/0x1ac
 [<c01376cb>] trace_hardirqs_on+0x118/0x16b
 [<c01225e2>] __do_softirq+0x49/0xa2
 [<c010595f>] do_softirq+0x60/0xdd
 [<c0506300>] _spin_unlock_irq+0x20/0x2c
 [<c0103e4f>] restore_nocheck+0x12/0x15
 [<c01440e1>] handle_fasteoi_irq+0x0/0x9b
 [<c0105a70>] do_IRQ+0x94/0xaa
 [<c0506300>] _spin_unlock_irq+0x20/0x2c
 [<c0104832>] common_interrupt+0x2e/0x34
 [<c0114703>] native_safe_halt+0x2/0x3
 [<c0102c01>] default_idle+0x44/0x65
 [<c010257f>] cpu_idle+0x42/0x50
 [<c076ea09>] start_kernel+0x26b/0x270
 [<c076e317>] unknown_bootoption+0x0/0x196
 =======================
irq event stamp: 559190
hardirqs last  enabled at (559190): [<c0507316>] kprobe_exceptions_notify+0x299/0x305
hardirqs last disabled at (559189): [<c05067bf>] do_int3+0x1d/0x95
softirqs last  enabled at (559172): [<c010595f>] do_softirq+0x60/0xdd
softirqs last disabled at (559181): [<c010595f>] do_softirq+0x60/0xdd
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

today, all oopses contain a version number of the kernel, which is nice
because the people who actually do bother to read the oops get this
vital bit of information always without having to ask the reporter in
another round trip.

However, WARN_ON() and many other dump_stack() users right now lack this
information; the patch below adds this. This information is essential
for getting people to use their time effectively when looking at these
things; in addition, it's essential for tools that try to collect
statistics about defects.

Please consider, since its so simple and important for long term kernel
quality processes.

The code is identical between 32/64 bit; a lot of this code should be
unified over time, the patch keeps the identical-ness intact.
Signed-off-by: NArjan van de Ven <arjan@linux.intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

Ensure we fixup the IRQ state before we hit any locking code.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

One of the easiest things to isolate is the pid printed in kernel log.
There was a patch, that made this for arch-independent code, this one makes
so for arch/xxx files.

It took some time to cross-compile it, but hopefully these are all the
printks in arch code.
Signed-off-by: NAlexey Dobriyan <adobriyan@openvz.org>
Signed-off-by: NPavel Emelyanov <xemul@openvz.org>
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This simplifies the io_apic.c __assign_irq_vector() logic and removes
the explicit SYSCALL_VECTOR check, and also allows for vectors to be
reserved by other mechanisms (ie. lguest).

[ tglx: arch/x86 adaptation ]
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

Don't want any lockdep or other fragile machinery to run during oopses.
Use raw spinlocks directly for oops locking.
Also disables irq flag tracing there.

[ tglx: arch/x86 adaptation ]
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

Both functions printk the same information, except for CRx and
debug registers in the show_registers() one and a bit different
manner. So move the common code into one place. This is already
done for x86_64, so I think it's worth having the same on i386.

This saves 100 bytes of .rodata section :) ...
   but only 8 from .text :(

[ tglx: arch/x86 adaptation ]
Signed-off-by: NPavel Emelyanov <xemul@openvz.org>
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

Typically the oops first lines look like this:

BUG: unable to handle kernel NULL pointer dereference at virtual address 00000000
 printing eip:
c049dfbd
*pde = 00000000
Oops: 0002 [#1]
PREEMPT SMP
...

Such output is gained with some ugly if (!nl) printk("\n"); code and
besides being a waste of lines, this is also annoying to read. The
following output looks better (and it is how it looks on x86_64):

BUG: unable to handle kernel NULL pointer dereference at virtual address 00000000
printing eip: c049dfbd *pde = 00000000
Oops: 0002 [#1] PREEMPT SMP
...

[ tglx: arch/x86 adaptation ]
Signed-off-by: NPavel Emelyanov <xemul@openvz.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

.. as they're never written to.

[ tglx: arch/x86 adaptation ]
Signed-off-by: NJan Beulich <jbeulich@novell.com>
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

Fix following section mismatch warning:
WARNING: vmlinux.o(.text+0xc88c): Section mismatch: reference to .init.text:trap_init_f00f_bug (between 'init_intel' and 'cpuid4_cache_lookup')

init_intel are __cpuint where trap_init_f00f_bug is __init.
Fixed by declaring trap_init_f00f_bug __cpuinit.

Moved the defintion of trap_init_f00f_bug to the sole user in init.c
so the ugly prototype in intel.c could get killed.

Frank van Maarseveen <frankvm@frankvm.com> supplied the .config used
to reproduce the warning.

[ tglx: arch/x86 adaptation ]

Cc: Frank van Maarseveen <frankvm@frankvm.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

Since the x86 merge, lots of files that referenced their own filenames
are no longer correct.  Rather than keep them up to date, just delete
them, as they add no real value.

Additionally:
- fix up comment formatting in scx200_32.c
- Remove a credit from myself in setup_64.c from a time when we had no SCM
- remove longwinded history from tsc_32.c which can be figured out from
  git.
Signed-off-by: NDave Jones <davej@redhat.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

lguest didn't initialize the kernel stack the way a real i386 kernel
does, and ended up triggering a corner-case in the stack frame checking
that doesn't happen on naive i386, and that the stack dumping didn't
handle quite right.

This makes the frame handling more correct, and tries to clarify the
code at the same time so that it's a bit more obvious what is going on.

Thanks to Rusty Russell for debugging the lguest failure-

Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>