Messages in this thread | | | Date | Sat, 19 May 2018 14:32:55 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH] x86/idt: Simplify the idt_setup_apic_and_irq_gates() |
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On Thu, 26 Apr 2018, Dou Liyang wrote:
> The vectors between FIRST_SYSTEM_VECTOR and NR_VECTORS are special IRQ > vectors used by the SMP architecture. But, if X86_LOCAL_APIC=n, it will > not be used, and the FIRST_SYSTEM_VECTOR is equal to NR_VECTORS.
Correct, but that function has nothing to do with FIRST_SYSTEM_VECTOR.
> diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c > index 2c3a1b4294eb..8b4174890706 100644 > --- a/arch/x86/kernel/idt.c > +++ b/arch/x86/kernel/idt.c > @@ -317,15 +317,16 @@ void __init idt_setup_apic_and_irq_gates(void) > set_intr_gate(i, entry); > } > > - for_each_clear_bit_from(i, system_vectors, NR_VECTORS) { > + /* > + * If X86_LOCAL_APIC=n, the FIRST_SYSTEM_VECTOR is equal to NR_VECTORS > + * Just consider the X86_LOCAL_APIC=y case > + */ > #ifdef CONFIG_X86_LOCAL_APIC > + for_each_clear_bit_from(i, system_vectors, NR_VECTORS) { > set_bit(i, system_vectors); > set_intr_gate(i, spurious_interrupt); > -#else > - entry = irq_entries_start + 8 * (i - FIRST_EXTERNAL_VECTOR); > - set_intr_gate(i, entry); > -#endif > } > +#endif
That change breaks the LOCAL_APIC=n case in a subtle way. What the function does is to set _ALL_ entries starting from FIRST_EXTERNAL_VECTOR up to NR_VECTORS in the IDT to a known target, except those which are already occupied by a system vector.
So for APIC=y this sets them to: spurious vector and for APIC=n it sets it to the corresppnding vector entry. You remove the latter...
Thanks,
tglx
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