Re: [RESEND PATCH 2/3] x86/apic/kexec: Enable legacy irq mode before jump to kexec/kdump kernel

[Dou Liyang <douly.fnst@cn.fujitsu.com>]

Hi Baoquan,

At 01/05/2018 12:38 PM, Baoquan He wrote:
> In commit
> 
> commit 522e66464467 ("x86/apic: Disable I/O APIC before shutdown of the local APIC").
> 
> lapic_shutdown() invocation is moved after disable_IO_APIC(). In fact
> in disable_IO_APIC(), it not only calls clear_IO_APIC() to disable
> IO-APIC, also sets sets LAPIC and IO-APIC to make system be PIC or
> Virtual wire mode. While the above commit putting disable_IO_APIC earlier
> causes local APIC is completely disabled. So the legacy irq mode is
> disabled too before jump to kexec/kdump kernel.
> 
I have a question:

As you said, Due to disable_IO_APIC() is triggered before
lapic_shutdown(), So the interrupt virtual wire mode will be disabled.

but, I found that:

After machine_crash_shutdown() is executed, Linux will call
machine_kexec(), and in machine_kexec(), disable_IO_APIC() will also be
called again, why it can't switch to virtual wire mode successfully? Or
is my understanding wrong?

+--------------+
| __crash_kexec|
+--------------+
|
|    +-------------------------+
+--> | machine_crash_shutdown  |
|    ++------------------------+
|     |
|     |  +-----------------+
|     +> | disable_IO_APIC |
|     |  +-----------------+
|     |
|     |  +----------------+
|     +-^+ lapic_shutdown |
|        +----------------+
|
|    +-------------------------+
+--> | machine_kexec           |
|    ++------------------------+
|     |
|     |  +-----------------+
|     +> | disable_IO_APIC |
|        +-----------------+
|
v

Thanks,
	dou.
> In normal kernel it defaults to be PIC mode or Virtual Wire mode during
> system initialization before APIC mode is enabled and this is done by
> BIOS initialization. But kexec/kdump kernel won't go through BIOS, so
> we should set system as PIC or Virtual Wire mode before jump to kdump
> kernel code directly.
> 
> So let's take clear_IO_APIC out from disable_IO_APIC and rename
> disable_IO_APIC as switch_to_legacy_irq_mode. Then only call clear_IO_APIC
> when IO-APIC need be disabled. And call switch_to_legacy_irq_mode before
> kexec/kdump jumping.
> 
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
>   arch/x86/include/asm/io_apic.h     |  3 ++-
>   arch/x86/kernel/apic/io_apic.c     | 12 ++++--------
>   arch/x86/kernel/crash.c            |  2 +-
>   arch/x86/kernel/machine_kexec_32.c | 15 +++++----------
>   arch/x86/kernel/machine_kexec_64.c | 15 +++++----------
>   arch/x86/kernel/reboot.c           |  2 +-
>   6 files changed, 18 insertions(+), 31 deletions(-)
> 
> diff --git a/arch/x86/include/asm/io_apic.h b/arch/x86/include/asm/io_apic.h
> index a8834dd546cd..e38ad3863a2c 100644
> --- a/arch/x86/include/asm/io_apic.h
> +++ b/arch/x86/include/asm/io_apic.h
> @@ -192,7 +192,8 @@ static inline unsigned int io_apic_read(unsigned int apic, unsigned int reg)
>   
>   extern void setup_IO_APIC(void);
>   extern void enable_IO_APIC(void);
> -extern void disable_IO_APIC(void);
> +extern void clear_IO_APIC (void);
> +extern void switch_to_legacy_irq_mode(void);
>   extern int IO_APIC_get_PCI_irq_vector(int bus, int devfn, int pin);
>   extern void print_IO_APICs(void);
>   #else  /* !CONFIG_X86_IO_APIC */
> diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
> index 8a7963421460..a47aa915d18c 100644
> --- a/arch/x86/kernel/apic/io_apic.c
> +++ b/arch/x86/kernel/apic/io_apic.c
> @@ -587,7 +587,7 @@ static void clear_IO_APIC_pin(unsigned int apic, unsigned int pin)
>   		       mpc_ioapic_id(apic), pin);
>   }
>   
> -static void clear_IO_APIC (void)
> +void clear_IO_APIC (void)
>   {
>   	int apic, pin;
>   
> @@ -1439,15 +1439,11 @@ void native_disable_io_apic(void)
>   }
>   
>   /*
> - * Not an __init, needed by the reboot code
> + * Not an __init, needed by kexec/kdump code.
> + * For safety IO-APIC and Local APIC need be cleared before this.
>    */
> -void disable_IO_APIC(void)
> +void switch_to_legacy_irq_mode(void)
>   {
> -	/*
> -	 * Clear the IO-APIC before rebooting:
> -	 */
> -	clear_IO_APIC();
> -
>   	if (!nr_legacy_irqs())
>   		return;
>   
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 10e74d4778a1..318ffeaaf55a 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -199,7 +199,7 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
>   #ifdef CONFIG_X86_IO_APIC
>   	/* Prevent crash_kexec() from deadlocking on ioapic_lock. */
>   	ioapic_zap_locks();
> -	disable_IO_APIC();
> +	clear_IO_APIC();
>   #endif
>   	lapic_shutdown();
>   #ifdef CONFIG_HPET_TIMER
> diff --git a/arch/x86/kernel/machine_kexec_32.c b/arch/x86/kernel/machine_kexec_32.c
> index edfede768688..7ab10d930cc6 100644
> --- a/arch/x86/kernel/machine_kexec_32.c
> +++ b/arch/x86/kernel/machine_kexec_32.c
> @@ -190,18 +190,13 @@ void machine_kexec(struct kimage *image)
>   	local_irq_disable();
>   	hw_breakpoint_disable();
>   
> -	if (image->preserve_context) {
>   #ifdef CONFIG_X86_IO_APIC
> -		/*
> -		 * We need to put APICs in legacy mode so that we can
> -		 * get timer interrupts in second kernel. kexec/kdump
> -		 * paths already have calls to disable_IO_APIC() in
> -		 * one form or other. kexec jump path also need
> -		 * one.
> -		 */
> -		disable_IO_APIC();
> +	/*
> +	 * We need to put APICs in legacy mode so that we can
> +	 * get timer interrupts in second kernel.
> +	 */
> +	switch_to_legacy_irq_mode();
>   #endif
> -	}
>   
>   	control_page = page_address(image->control_code_page);
>   	memcpy(control_page, relocate_kernel, KEXEC_CONTROL_CODE_MAX_SIZE);
> diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
> index 1f790cf9d38f..b5c0cbed6791 100644
> --- a/arch/x86/kernel/machine_kexec_64.c
> +++ b/arch/x86/kernel/machine_kexec_64.c
> @@ -288,18 +288,13 @@ void machine_kexec(struct kimage *image)
>   	local_irq_disable();
>   	hw_breakpoint_disable();
>   
> -	if (image->preserve_context) {
>   #ifdef CONFIG_X86_IO_APIC
> -		/*
> -		 * We need to put APICs in legacy mode so that we can
> -		 * get timer interrupts in second kernel. kexec/kdump
> -		 * paths already have calls to disable_IO_APIC() in
> -		 * one form or other. kexec jump path also need
> -		 * one.
> -		 */
> -		disable_IO_APIC();
> +	/*
> +	 * We need to put APICs in legacy mode so that we can
> +	 * get timer interrupts in second kernel.
> +	 */
> +	switch_to_legacy_irq_mode();
>   #endif
> -	}
>   
>   	control_page = page_address(image->control_code_page) + PAGE_SIZE;
>   	memcpy(control_page, relocate_kernel, KEXEC_CONTROL_CODE_MAX_SIZE);
> diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
> index 2126b9d27c34..b70cc0f38a29 100644
> --- a/arch/x86/kernel/reboot.c
> +++ b/arch/x86/kernel/reboot.c
> @@ -666,7 +666,7 @@ void native_machine_shutdown(void)
>   	 * Even without the erratum, it still makes sense to quiet IO APIC
>   	 * before disabling Local APIC.
>   	 */
> -	disable_IO_APIC();
> +	clear_IO_APIC();
>   #endif
>   
>   #ifdef CONFIG_SMP
>