Re: [PATCH v3 0/5] x86/apic: Fix restoring boot irq mode in reboot and kexec/kdump

[Dou Liyang]

Hi all,

One thing confused me.

The disconnect_bsp_APIC() may restore the interrupt delivery mode into
virtual wire mode. it uses the vector F as the spurious interrput, But,
IMO, using the vector 0xFF(SPURIOUS_APIC_VECTOR) may more suitable and
will give us more detail. Why the disconnect_bsp_APIC() use vector F
here?

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 25ddf02598d2..550deaad6a9a 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -2130,7 +2130,7 @@ void disconnect_bsp_APIC(int virt_wire_setup)
        value = apic_read(APIC_SPIV);
        value &= ~APIC_VECTOR_MASK;
        value |= APIC_SPIV_APIC_ENABLED;
-       value |= 0xf;
+       value |= SPURIOUS_APIC_VECTOR;
        apic_write(APIC_SPIV, value);

        if (!virt_wire_setup) {

Thanks,
	dou

At 02/09/2018 08:10 PM, Baoquan He wrote:
> A regression bug was introduced in below commit.
> commit 522e66464467 ("x86/apic: Disable I/O APIC before shutdown of the local APIC")
>
> It caused the action to fail which we try to restore boot irq mode
> in reboot and kexec/kdump. Details can be seen in patch 0002.
>
> Warning can always be seen during kdump kernel boot on qemu/kvm
> platform. Our customer even saw casual kdump kernel hang once in
> ~30 attempts during stress testing of kdump on KVM machine.
>
> This is v3 post, patches are rearranged and changed according to
> Eric's suggestions.
>
> Baoquan He (5):
>    x86/apic: Split out restore_boot_irq_mode from disable_IO_APIC
>    x86/apic: Fix restoring boot irq mode in reboot and kexec/kdump
>    x86/apic: Remove useless disable_IO_APIC
>    x86/apic: Rename variable/function related to x86_io_apic_ops
>    x86/apic: Set up through-local-APIC on boot CPU if 'noapic' specified
>
>   arch/x86/include/asm/io_apic.h     |  9 +++++----
>   arch/x86/include/asm/x86_init.h    |  8 ++++----
>   arch/x86/kernel/apic/apic.c        |  2 +-
>   arch/x86/kernel/apic/io_apic.c     | 16 ++++------------
>   arch/x86/kernel/crash.c            |  3 ++-
>   arch/x86/kernel/machine_kexec_32.c |  7 +++----
>   arch/x86/kernel/machine_kexec_64.c |  7 +++----
>   arch/x86/kernel/reboot.c           |  3 ++-
>   arch/x86/kernel/x86_init.c         |  6 +++---
>   arch/x86/xen/apic.c                |  2 +-
>   drivers/iommu/irq_remapping.c      |  4 ++--
>   11 files changed, 30 insertions(+), 37 deletions(-)