linux-kernel - Re: [patch 1/2] x86/cpu: Init exception handling from cpu_init

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Message-ID: <ccbd2f11-bb74-19bd-cf5c-d524625f9a0d@linux.alibaba.com>
Date:   Sun, 9 May 2021 07:40:34 +0800
From:   Lai Jiangshan <laijs@...ux.alibaba.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Joerg Roedel <joro@...tes.org>,
        Borislav Petkov <bp@...e.de>
Subject: Re: [patch 1/2] x86/cpu: Init exception handling from
 cpu_init_secondary()



On 2021/5/7 19:02, Thomas Gleixner wrote:
> From: Borislav Petkov <bp@...e.de>
> 
> SEV-ES guests require properly setup task register with which the TSS
> descriptor in the GDT can be located so that the IST-type #VC exception
> handler which they need to function properly, can be executed.
> 
> This setup needs to happen before attempting to load microcode in
> ucode_cpu_init() on secondary CPUs which can cause such #VC exceptions.
> 
> Simplify the machinery by running that exception setup from a new function
> cpu_init_secondary() and explicitly call cpu_init_exception_handling() for
> the boot CPU before cpu_init(). The latter prepares for fixing and
> simplifying the exception/IST setup on the boot CPU.
> 
> There should be no functional changes resulting from this patch.
> 
> [ tglx: Reworked it so cpu_init_exception_handling() stays separate ]
> 
> Signed-off-by: Borislav Petkov <bp@...e.de>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> 
> ---
>   arch/x86/include/asm/processor.h |    1 +
>   arch/x86/kernel/cpu/common.c     |   24 +++++++++++-------------
>   arch/x86/kernel/traps.c          |    4 +---
>   3 files changed, 13 insertions(+), 16 deletions(-)
> 
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -663,6 +663,7 @@ extern void load_direct_gdt(int);
>   extern void load_fixmap_gdt(int);
>   extern void load_percpu_segment(int);
>   extern void cpu_init(void);
> +extern void cpu_init_secondary(void);
>   extern void cpu_init_exception_handling(void);
>   extern void cr4_init(void);
>   
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1938,13 +1938,12 @@ void cpu_init_exception_handling(void)
>   
>   /*
>    * cpu_init() initializes state that is per-CPU. Some data is already
> - * initialized (naturally) in the bootstrap process, such as the GDT
> - * and IDT. We reload them nevertheless, this function acts as a
> - * 'CPU state barrier', nothing should get across.
> + * initialized (naturally) in the bootstrap process, such as the GDT.  We
> + * reload it nevertheless, this function acts as a 'CPU state barrier',
> + * nothing should get across.
>    */
>   void cpu_init(void)
>   {
> -	struct tss_struct *tss = this_cpu_ptr(&cpu_tss_rw);
>   	struct task_struct *cur = current;
>   	int cpu = raw_smp_processor_id();
>   
> @@ -1957,8 +1956,6 @@ void cpu_init(void)
>   	    early_cpu_to_node(cpu) != NUMA_NO_NODE)
>   		set_numa_node(early_cpu_to_node(cpu));
>   #endif
> -	setup_getcpu(cpu);
> -
>   	pr_debug("Initializing CPU#%d\n", cpu);
>   
>   	if (IS_ENABLED(CONFIG_X86_64) || cpu_feature_enabled(X86_FEATURE_VME) ||
> @@ -1970,7 +1967,6 @@ void cpu_init(void)
>   	 * and set up the GDT descriptor:
>   	 */
>   	switch_to_new_gdt(cpu);
> -	load_current_idt();
>   
>   	if (IS_ENABLED(CONFIG_X86_64)) {
>   		loadsegment(fs, 0);
> @@ -1990,12 +1986,6 @@ void cpu_init(void)
>   	initialize_tlbstate_and_flush();
>   	enter_lazy_tlb(&init_mm, cur);
>   
> -	/* Initialize the TSS. */
> -	tss_setup_ist(tss);
> -	tss_setup_io_bitmap(tss);
> -	set_tss_desc(cpu, &get_cpu_entry_area(cpu)->tss.x86_tss);
> -
> -	load_TR_desc();
>   	/*
>   	 * sp0 points to the entry trampoline stack regardless of what task
>   	 * is running.
> @@ -2017,6 +2007,14 @@ void cpu_init(void)
>   	load_fixmap_gdt(cpu);
>   }
>   
> +#ifdef CONFIG_SMP
> +void cpu_init_secondary(void)
> +{
> +	cpu_init_exception_handling();
> +	cpu_init();
> +}
> +#endif

Hello

No code invokes this function in this patch.

Forgot to invoke it from start_secondary() or somewhere?

Thanks
Lai

> +
>   /*
>    * The microcode loader calls this upon late microcode load to recheck features,
>    * only when microcode has been updated. Caller holds microcode_mutex and CPU
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -1162,9 +1162,7 @@ void __init trap_init(void)
>   
>   	idt_setup_traps();
>   
> -	/*
> -	 * Should be a barrier for any external CPU state:
> -	 */
> +	cpu_init_exception_handling();
>   	cpu_init();
>   
>   	idt_setup_ist_traps();
>