linux/arch/sparc/prom/p1275.c
David S. Miller ef3e035c3a sparc64: Fix register corruption in top-most kernel stack frame during boot.
Meelis Roos reported that kernels built with gcc-4.9 do not boot, we
eventually narrowed this down to only impacting machines using
UltraSPARC-III and derivitive cpus.

The crash happens right when the first user process is spawned:

[   54.451346] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000004
[   54.451346]
[   54.571516] CPU: 1 PID: 1 Comm: init Not tainted 3.16.0-rc2-00211-gd7933ab 
[   54.666431] Call Trace:
[   54.698453]  [0000000000762f8c] panic+0xb0/0x224
[   54.759071]  [000000000045cf68] do_exit+0x948/0x960
[   54.823123]  [000000000042cbc0] fault_in_user_windows+0xe0/0x100
[   54.902036]  [0000000000404ad0] __handle_user_windows+0x0/0x10
[   54.978662] Press Stop-A (L1-A) to return to the boot prom
[   55.050713] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000004

Further investigation showed that compiling only per_cpu_patch() with
an older compiler fixes the boot.

Detailed analysis showed that the function is not being miscompiled by
gcc-4.9, but it is using a different register allocation ordering.

With the gcc-4.9 compiled function, something during the code patching
causes some of the %i* input registers to get corrupted.  Perhaps
we have a TLB miss path into the firmware that is deep enough to
cause a register window spill and subsequent restore when we get
back from the TLB miss trap.

Let's plug this up by doing two things:

1) Stop using the firmware stack for client interface calls into
   the firmware.  Just use the kernel's stack.

2) As soon as we can, call into a new function "start_early_boot()"
   to put a one-register-window buffer between the firmware's
   deepest stack frame and the top-most initial kernel one.

Reported-by: Meelis Roos <mroos@linux.ee>
Tested-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-24 09:52:49 -07:00

55 lines
1.1 KiB
C

/*
* p1275.c: Sun IEEE 1275 PROM low level interface routines
*
* Copyright (C) 1996,1997 Jakub Jelinek (jj@sunsite.mff.cuni.cz)
*/
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/smp.h>
#include <linux/string.h>
#include <linux/spinlock.h>
#include <linux/irqflags.h>
#include <asm/openprom.h>
#include <asm/oplib.h>
#include <asm/spitfire.h>
#include <asm/pstate.h>
#include <asm/ldc.h>
struct {
long prom_callback; /* 0x00 */
void (*prom_cif_handler)(long *); /* 0x08 */
} p1275buf;
extern void prom_world(int);
extern void prom_cif_direct(unsigned long *args);
extern void prom_cif_callback(void);
/*
* This provides SMP safety on the p1275buf.
*/
DEFINE_RAW_SPINLOCK(prom_entry_lock);
void p1275_cmd_direct(unsigned long *args)
{
unsigned long flags;
local_save_flags(flags);
local_irq_restore((unsigned long)PIL_NMI);
raw_spin_lock(&prom_entry_lock);
prom_world(1);
prom_cif_direct(args);
prom_world(0);
raw_spin_unlock(&prom_entry_lock);
local_irq_restore(flags);
}
void prom_cif_init(void *cif_handler, void *cif_stack)
{
p1275buf.prom_cif_handler = (void (*)(long *))cif_handler;
}