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SubjectRe: x86: Spurious vectors not handled robustly
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On 24.06.19 12:09, Thomas Gleixner wrote:
> Jan,
>
> On Mon, 24 Jun 2019, Jan Kiszka wrote:
>> probably since "x86: Avoid building unused IRQ entry stubs" (2414e021ac8d),
>> the kernel can no longer tell spurious IRQs by the APIC apart from spuriously
>> triggered unused vectors.
>
> Err. It does.
>
>> We've managed to trigger such a cause with the Jailhouse hypervisor
>> (incorrectly injected MANAGED_IRQ_SHUTDOWN_VECTOR), and the result was
>> not only a misreport of the vector number (0xff instead of 0xef - took me
>> a while...), but also stalled interrupts of equal and lower priority
>> because a spurious interrupt is not (and must not be) acknowledged.
>
> That does not make sense.
>
> __visible void __irq_entry smp_spurious_interrupt(struct pt_regs *regs)
> {
> u8 vector = ~regs->orig_ax;
> u32 v;
>
> entering_irq();
> trace_spurious_apic_entry(vector);
> /*
> * Check if this really is a spurious interrupt and ACK it
> * if it is a vectored one. Just in case...
> */
> v = apic_read(APIC_ISR + ((vector & ~0x1f) >> 1));
> if (v & (1 << (vector & 0x1f)))
> ack_APIC_irq();
>
> If it is a vectored one it _IS_ acked.
>
> inc_irq_stat(irq_spurious_count);
>
> /* see sw-dev-man vol 3, chapter 7.4.13.5 */
> pr_info("spurious APIC interrupt through vector %02x on CPU#%d, "
> "should never happen.\n", vector, smp_processor_id());
>
> and the vector through which that comes is printed correctly, unless
> regs->orig_ax is hosed.

...which is exactly the case: Since that commit, all unused vectors share the
same entry point, spurious_interrupt, see idt_setup_apic_and_irq_gates(). And
that entry point sets orig_ax to ~0xff.

Jan

--
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux

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