Hi Thomas,
At 05/19/2018 08:32 PM, Thomas Gleixner wrote:
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.
Oops, sorry, when I reread, my changelog even made me misunderstand.
the patch hided it.
void __init idt_setup_apic_and_irq_gates(void)
...
for_each_clear_bit_from(i, system_vectors, FIRST_SYSTEM_VECTOR)
^^^^^^^^^^^^^^^^^^^
...
for_each_clear_bit_from(i, system_vectors, NR_VECTORS)
What I want to say is:
In the APIC=n system, the FIRST_SYSTEM_VECTOR is equal to
NR_VECTORS, So all entries has been set by
for_each_clear_bit_from(i, system_vectors, FIRST_SYSTEM_VECTOR)
...
the following setup code for APIC=n is redundant. Just setup gates for
APIC=y.
If it is OK, I will send v2.
Thanks,
dou
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
