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

[Baoquan He]

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.

> 
> +--------------+
> | __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@xxxxxxxxxx>
> > ---
> >   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
> > 
> 
>