3.16.57-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Wang Nan <wangnan0@xxxxxxxxxx> commit b4d8327024637cb2a1f7910dcb5d0ad7a096f473 upstream. Before this patch early_trap_init() installs DEBUG_STACK for X86_TRAP_BP and X86_TRAP_DB. However, DEBUG_STACK doesn't work correctly until cpu_init() <-- trap_init(). This patch passes 0 to set_intr_gate_ist() and set_system_intr_gate_ist() instead of DEBUG_STACK to let it use same stack as kernel, and installs DEBUG_STACK for them in trap_init(). As core runs at ring 0 between early_trap_init() and trap_init(), there is no chance to get a bad stack before trap_init(). As NMI is also enabled in trap_init(), we don't need to care about is_debug_stack() and related things used in arch/x86/kernel/nmi.c. Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx> Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx> Acked-by: Steven Rostedt <rostedt@xxxxxxxxxxx> Cc: <dave.hansen@xxxxxxxxxxxxxxx> Cc: <lizefan@xxxxxxxxxx> Cc: <luto@xxxxxxxxxxxxxx> Cc: <oleg@xxxxxxxxxx> Link: http://lkml.kernel.org/r/1424929779-13174-1-git-send-email-wangnan0@xxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> --- arch/x86/kernel/traps.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -773,9 +773,17 @@ dotraplinkage void do_iret_error(struct /* Set of traps needed for early debugging. */ void __init early_trap_init(void) { - set_intr_gate_ist(X86_TRAP_DB, &debug, DEBUG_STACK); + /* + * Don't set ist to DEBUG_STACK as it doesn't work until TSS is + * ready in cpu_init() <-- trap_init(). Before trap_init(), CPU + * runs at ring 0 so it is impossible to hit an invalid stack. + * Using the original stack works well enough at this early + * stage. DEBUG_STACK will be equipped after cpu_init() in + * trap_init(). + */ + set_intr_gate_ist(X86_TRAP_DB, &debug, 0); /* int3 can be called from all */ - set_system_intr_gate_ist(X86_TRAP_BP, &int3, DEBUG_STACK); + set_system_intr_gate_ist(X86_TRAP_BP, &int3, 0); #ifdef CONFIG_X86_32 set_intr_gate(X86_TRAP_PF, page_fault); #endif @@ -853,6 +861,15 @@ void __init trap_init(void) */ cpu_init(); + /* + * X86_TRAP_DB and X86_TRAP_BP have been set + * in early_trap_init(). However, DEBUG_STACK works only after + * cpu_init() loads TSS. See comments in early_trap_init(). + */ + set_intr_gate_ist(X86_TRAP_DB, &debug, DEBUG_STACK); + /* int3 can be called from all */ + set_system_intr_gate_ist(X86_TRAP_BP, &int3, DEBUG_STACK); + x86_init.irqs.trap_init(); #ifdef CONFIG_X86_64
