Re: [PATCH v2] x86, traps: separate set_intr_gate() and cleanup early_trap_init().

[Wang Nan <wangnan0@huawei.com>]

Hi Andy Lutomirski,

Do you have any comment on this patch?

Thank you.

On 2015/2/27 12:19, Wang Nan wrote:
> As early_trap_init() doesn't use IST, replace set_intr_gate_ist() and
> set_system_intr_gate_ist() with their standard counterparts.
> 
> set_intr_gate() requires a trace_debug symbol which we don't have and
> won't use. This patch seprates set_intr_gate() into 2 parts, and uses
> base version in early_trap_init().
> 
> Signed-off-by: Wang Nan <wangnan0@huawei.com>
> ---
> 
> Hi Andy Lutomirski,
> 
>    This patch should be less tricky than previous one [1]. I also tried
>    to renaming all set_intr_gate(), but it causes too many code changes,
>    so I think you will be satisfied with this one.
> 
> Thank you!
> 
> [1] https://lkml.org/lkml/2015/2/26/770
> 
> ---
>  arch/x86/include/asm/desc.h |  7 ++++++-
>  arch/x86/kernel/traps.c     | 20 ++++++++++++--------
>  2 files changed, 18 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
> index a94b82e..a0bf89f 100644
> --- a/arch/x86/include/asm/desc.h
> +++ b/arch/x86/include/asm/desc.h
> @@ -376,11 +376,16 @@ static inline void _set_gate(int gate, unsigned type, void *addr,
>   * Pentium F0 0F bugfix can have resulted in the mapped
>   * IDT being write-protected.
>   */
> -#define set_intr_gate(n, addr)						\
> +#define set_intr_gate_notrace(n, addr)					\
>  	do {								\
>  		BUG_ON((unsigned)n > 0xFF);				\
>  		_set_gate(n, GATE_INTERRUPT, (void *)addr, 0, 0,	\
>  			  __KERNEL_CS);					\
> +	} while (0)
> +
> +#define set_intr_gate(n, addr)						\
> +	do {								\
> +		set_intr_gate_notrace(n, addr);				\
>  		_trace_set_gate(n, GATE_INTERRUPT, (void *)trace_##addr,\
>  				0, 0, __KERNEL_CS);			\
>  	} while (0)
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index 4281988..9965bd1 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -926,16 +926,20 @@ dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code)
>  void __init early_trap_init(void)
>  {
>  	/*
> -	 * 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
> +	 * Don't use IST to set 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().
> +	 *
> +	 * We don't need to set trace_idt_table like set_intr_gate(),
> +	 * since we don't have trace_debug and it will be reset to
> +	 * 'debug' in trap_init() by set_intr_gate_ist().
>  	 */
> -	set_intr_gate_ist(X86_TRAP_DB, &debug, 0);
> +	set_intr_gate_notrace(X86_TRAP_DB, debug);
>  	/* int3 can be called from all */
> -	set_system_intr_gate_ist(X86_TRAP_BP, &int3, 0);
> +	set_system_intr_gate(X86_TRAP_BP, &int3);
>  #ifdef CONFIG_X86_32
>  	set_intr_gate(X86_TRAP_PF, page_fault);
>  #endif
> @@ -1015,7 +1019,7 @@ void __init trap_init(void)
>  
>  	/*
>  	 * X86_TRAP_DB and X86_TRAP_BP have been set
> -	 * in early_trap_init(). However, DEBUG_STACK works only after
> +	 * in early_trap_init(). However, ITS works only after
>  	 * cpu_init() loads TSS. See comments in early_trap_init().
>  	 */
>  	set_intr_gate_ist(X86_TRAP_DB, &debug, DEBUG_STACK);
>