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Date: Fri, 19 Jan 2018 14:24:19 +0800
From: Dou Liyang <douly.fnst@...fujitsu.com>
To: Baoquan He <bhe@...hat.com>
CC: <linux-kernel@...r.kernel.org>, <mingo@...hat.com>,
<tglx@...utronix.de>, <hpa@...or.com>, <x86@...nel.org>,
<rostedt@...dmis.org>, <jgross@...e.com>, <peterz@...radead.org>,
<uobergfe@...hat.com>, <joro@...tes.org>
Subject: Re: [RESEND PATCH 2/3] x86/apic/kexec: Enable legacy irq mode before
jump to kexec/kdump kernel
Hi Baoquan,
At 01/17/2018 06:08 PM, Baoquan He wrote:
> On 01/17/18 at 05:47pm, Dou Liyang wrote:
>> 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?
> The disable_IO_APIC() calling has a condition check,
>
> if (image->preserve_context) {
> disable_IO_APIC();
> }
>
> For preserve_context case, it comes from kernel_kexec(). You can check
> it in kexec man page, that is another scenario we use kexec for. But not
> kexec and kdump.
>
Understood!
This patch looks good to me and I also tested it, it's OK.
Thanks,
dou.
>>
>> +--------------+
>> | __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@...hat.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
>>>
>>
>>
>
>
>
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