linux.git/include/asm-x86/system.h, branch v2.6.27

x86: fix savesegment() bug causing crashes on 64-bit

2008-07-11T17:51:47+00:00

i spent a fair amount of time chasing a 64-bit bootup crash that manifested
itself as bootup segfaults:

  S10network[1825]: segfault at 7f3e2b5d16b8 ip 00000031108748c9 sp 00007fffb9c14c70 error 4 in libc-2.7.so[3110800000+14d000]

eventually causing init to die and panic the system:

  Kernel panic - not syncing: Attempted to kill init!
  Pid: 1, comm: init Not tainted 2.6.26-rc9-tip #13878

after a maratonic bisection session, the bad commit turned out to be:

| b7675791859075418199c7af86a116ea34eaf5bd is first bad commit
| commit b7675791859075418199c7af86a116ea34eaf5bd
| Author: Jeremy Fitzhardinge 
| Date:   Wed Jun 25 00:19:00 2008 -0400
|
|     x86: remove open-coded save/load segment operations
|
|     This removes a pile of buggy open-coded implementations of savesegment
|     and loadsegment.

after some more bisection of this patch itself, it turns out that what
makes the difference are the savesegment() changes to __switch_to().

Taking a look at this portion of arch/x86/kernel/process_64.o revealed
this crutial difference:

| good:    99c:       8c e0                   mov    %fs,%eax
|          99e:       89 45 cc                mov    %eax,-0x34(%rbp)
|
| bad:     99c:       8c 65 cc                mov    %fs,-0x34(%rbp)

which is due to:

|                 unsigned fsindex;
| -               asm volatile("movl %%fs,%0" : "=r" (fsindex));
| +               savesegment(fs, fsindex);

savesegment() is implemented as:

 #define savesegment(seg, value)                                \
          asm("mov %%" #seg ",%0":"=rm" (value) : : "memory")

note the "m" modifier - it allows GCC to generate the segment move
into a memory operand as well.

But regarding segment operands there's a subtle detail in the x86
instruction set: the above 16-bit moves are zero-extend, but only
if it goes to a register.

If it goes to a memory operand, -0x34(%rbp) in the above case, there's
no zero-extend to 32-bit and the instruction will only save 16 bits
instead of the intended 32-bit.

The other 16 bits is random data - which can cause problems when that
value is used later on.

The solution is to only allow segment operands to go to registers.
This fix allows my test-system to boot up without crashing.

Signed-off-by: Ingo Molnar

x86/paravirt, 64-bit: make load_gs_index() a paravirt operation

2008-07-08T11:15:58+00:00

Signed-off-by: Eduardo Habkost 
Signed-off-by: Jeremy Fitzhardinge 
Cc: xen-devel 
Cc: Stephen Tweedie 
Cc: Eduardo Habkost 
Cc: Mark McLoughlin 
Signed-off-by: Ingo Molnar

x86: add memory clobber to save/loadsegment

2008-07-08T11:10:23+00:00

Add "memory" clobbers to savesegment and loadsegment, since they can
affect memory accesses and we never want the compiler to reorder them
with respect to memory references.

Signed-off-by: Jeremy Fitzhardinge 
Cc: xen-devel 
Cc: Stephen Tweedie 
Cc: Eduardo Habkost 
Cc: Mark McLoughlin 
Signed-off-by: Ingo Molnar

Merge branch 'x86/mpparse' into x86/devel

2008-07-08T09:14:58+00:00

Conflicts:

	arch/x86/Kconfig
	arch/x86/kernel/io_apic_32.c
	arch/x86/kernel/setup_64.c
	arch/x86/mm/init_32.c

Signed-off-by: Ingo Molnar

x86: use symbolic constant in stts()

2008-05-27T08:04:29+00:00

Signed-off-by: Jeremy Fitzhardinge 
Signed-off-by: Thomas Gleixner

x86: move es7000_plat out of mpparse.c

2008-05-25T08:55:12+00:00

Signed-off-by: Alexey Starikovskiy 
Signed-off-by: Ingo Molnar

include/asm-x86/system.h: checkpatch cleanups - formatting only

2008-04-17T15:41:28+00:00

Signed-off-by: Joe Perches 
Signed-off-by: Ingo Molnar

x86: fix switch_to() clobbers

2008-04-17T15:40:52+00:00

Liu Pingfan noticed that switch_to() clobbers more registers than its
asm constraints specify.

We get away with this due to luck mostly - schedule()
by its nature only has 'local' state which gets reloaded
automatically. Fix it nevertheless, we could hit this anytime.

it turns out that with the extra constraints gcc manages to make
schedule() even more compact:

   text	   data	    bss	    dec	    hex	filename
  28626	    684	   2640	  31950	   7cce	sched.o.before
  28613	    684	   2640	  31937	   7cc1	sched.o.after

Reported-by: Liu Pingfan 
Signed-off-by: Ingo Molnar

x86: clean up switch_to()

2008-04-17T15:40:52+00:00

Make the code more readable and more hackable:

 - use symbolic asm parameters
 - use readable indentation
 - add comments that explains the details

No code changed:

kernel/sched.o:

   text	   data	    bss	    dec	    hex	filename
  28626	    684	   2640	  31950	   7cce	sched.o.before
  28626	    684	   2640	  31950	   7cce	sched.o.after

md5:
   2823d406c18b781975cdb2e7cfea0059  sched.o.before.asm
   2823d406c18b781975cdb2e7cfea0059  sched.o.after.asm

Signed-off-by: Ingo Molnar

x86: wmb() confusion in system.h

2008-04-17T15:40:52+00:00

Comment says wmb is a nop, but it is implemented as lock addl
below... Should it be compiled to nop if we know we are running on
"good" Intel cpu?

At least remove confusing comment for now.

Signed-off-by: Pavel Machek 
Signed-off-by: Ingo Molnar