linux-kernel - Re: [PATCH v2] x86, traps: separate set_intr_gate() and cleanup early_trap

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Message-ID: <CALCETrXT+R2==m4khAfLMVOfAqcoE1Ji0r7VZok4+AD5E2qNCA@mail.gmail.com>
Date:	Mon, 2 Mar 2015 09:06:44 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	Li Zefan <lizefan@...wei.com>, Ingo Molnar <mingo@...nel.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH v2] x86, traps: separate set_intr_gate() and cleanup early_trap_init().

On Thu, Feb 26, 2015 at 8:19 PM, Wang Nan <wangnan0@...wei.com> 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@...wei.com>

Looks good to me.  Ingo?

--Andy

> ---
>
> 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);
> --
> 1.8.4
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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