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


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