[Qemu-devel] GICv3/GIC-500

[Shlomo Pongratz]

Hi,

I'm trying to implement GICv3 (actually GIC-500) in order to support more than 
8 cores for ARM64.
Up to 24 cores I didn't notice any significant problems (just slow boot) but 
with 64 or 32 cores the Linux kernel is usually got stuck, seldom it completes 
the boot.
When examining the registers I see that all cores except one is stuck in ether 
"PC=ffffffc000108a18" or "PC=ffffffc000108a18" which is according to objdump in:
kernel/stop_machine.c::multi_cpu_stop

        msdata->state = newstate;
ffffffc000108a10:       b9002261        str     w1, [x19,#32]
ffffffc000108a14:       2a1403e1        mov     w1, w20
                        default:
                                break;
                        }
                        ack_state(msdata);
                }
        } while (curstate != MULTI_STOP_EXIT);
ffffffc000108a18:       7100103f        cmp     w1, #0x4
ffffffc000108a1c:       54000120        b.eq    ffffffc000108a40 
<multi_cpu_stop+0xcc>

        /* Simple state machine */
        do {
                /* Chill out and ensure we re-read multi_stop_state. */
                cpu_relax();
                if (msdata->state != curstate) {
ffffffc000108a20:       b9402274        ldr     w20, [x19,#32]
ffffffc000108a24:       6b01029f        cmp     w20, w1

There is one CPU however (and there is always such CPU) is stuck in 
"PC=ffffffc0002cd9f4" which is in

drivers/irqchip/irq-gic-v3.c ::gic_eoi_irq

static void gic_eoi_irq(struct irq_data *d)
{
        gic_write_eoir(gic_irq(d));
ffffffc0002cd9ec:       b9400800        ldr     w0, [x0,#8]
ffffffc0002cd9f0:       d518cc20        msr     s3_0_c12_c12_1, x0
ffffffc0002cd9f4:       d5033fdf        isb
}
ffffffc0002cd9f8:       d65f03c0        ret

But according to target-arm/translate-a64.c::handle_sync "isb" is translated as 
no-op!
BTW X00=000000000000001b is the virtual timer IRQ-27, so it seems that only 
this core (number 7 at this point)  is getting clock.

Dose anyone can give me an advice of how to further debug this issue?

Best regards,

S.P.