> [<C0181164>] do_apm_timer
[...]
> [<C0109D20>] ret_from_intr
> [<C0108A0B>] __switch_to+0x73
> Common to all the GPFs is, that I was running programs under WINE at the
> time of the crash. (When not running WINE, the same configuration hums
> along happily for days.)
hm, the problem is that the APM bottom half runs during context switching.
When the bh is executed at a point where we have already switched the LDT,
but have not yet saved the segments, it can cause a crash by
saving/restoring illegal segment registers.
there are several solutions to this problem:
- disable interrupts during switch_to()
- disallow segment manipulation of any kind during interrupts (ie.
changes to APM)
- make the switch_to() code safe wrt segment saves without
disabling IRQs, by zeroing out segment registers. (zeroing
segment registers takes exactly 1 cycle on my PII)
i've implemented this last one [attached], does it fix your crashes? The
best way you can speed up the crash further is to define HZ as 1000 or
10000 in asm/param.h.
is there any other place in the kernel where segment registers might hold
invalid contents?
-- mingo
--- linux/arch/i386/kernel/process.c.orig Mon Aug 24 15:01:52 1998
+++ linux/arch/i386/kernel/process.c Mon Aug 24 15:19:03 1998
@@ -727,10 +727,6 @@
gdt_table[next->tss.tr >> 3].b &= 0xfffffdff;
asm volatile("ltr %0": :"g" (*(unsigned short *)&next->tss.tr));
- /* Re-load LDT if necessary */
- if (next->mm->segments != prev->mm->segments)
- asm volatile("lldt %0": :"g" (*(unsigned short *)&next->tss.ldt));
-
/* Re-load page tables */
if (next->tss.cr3 != prev->tss.cr3)
asm volatile("movl %0,%%cr3": :"r" (next->tss.cr3));
@@ -742,6 +738,17 @@
*/
asm volatile("movl %%fs,%0":"=m" (*(int *)&prev->tss.fs));
asm volatile("movl %%gs,%0":"=m" (*(int *)&prev->tss.gs));
+
+ /* Re-load LDT if necessary */
+ if (next->mm->segments != prev->mm->segments) {
+ /*
+ * careful, we always want to have valid segments.
+ * not only APM but hw-vendor SMM features matter too
+ */
+ asm volatile("movl %0, %%fs"::"r"(0));
+ asm volatile("movl %0, %%gs"::"r"(0));
+ asm volatile("lldt %0": :"g" (*(unsigned short *)&next->tss.ldt));
+ }
loadsegment(fs,next->tss.fs);
loadsegment(gs,next->tss.gs);
-
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