From ef3e035c3a9b81da8a778bc333d10637acf6c199 Mon Sep 17 00:00:00 2001 From: "David S. Miller" Date: Thu, 23 Oct 2014 12:58:13 -0700 Subject: 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 #96 [ 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 Tested-by: Meelis Roos Signed-off-by: David S. Miller --- arch/sparc/prom/p1275.c | 2 -- 1 file changed, 2 deletions(-) (limited to 'arch/sparc/prom/p1275.c') diff --git a/arch/sparc/prom/p1275.c b/arch/sparc/prom/p1275.c index b2340f008ae0..545d8bb79b65 100644 --- a/arch/sparc/prom/p1275.c +++ b/arch/sparc/prom/p1275.c @@ -20,7 +20,6 @@ struct { long prom_callback; /* 0x00 */ void (*prom_cif_handler)(long *); /* 0x08 */ - unsigned long prom_cif_stack; /* 0x10 */ } p1275buf; extern void prom_world(int); @@ -52,5 +51,4 @@ void p1275_cmd_direct(unsigned long *args) void prom_cif_init(void *cif_handler, void *cif_stack) { p1275buf.prom_cif_handler = (void (*)(long *))cif_handler; - p1275buf.prom_cif_stack = (unsigned long)cif_stack; } -- cgit v1.2.3-59-g8ed1b