Re: [RFC 0/3] try to solve the DMA to MMIO issue

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 9/3/20 1:28 PM, Peter Maydell wrote:
> On Thu, 3 Sep 2020 at 12:24, Li Qiang <liq3ea@gmail.com> wrote:
>> Peter Maydell <peter.maydell@linaro.org> 于2020年9月3日周四 下午7:19写道：
>>> No. Any device can have an inbound or outbound qemu_irq line.
>>> We use them not just for actual IRQ lines but for any
>>> situation where we need to pass an on-or-off signal from
>>> one device to another.
>>
>> Could you please provide some example, I haven't noticed this before.
> 
> Look at any device that calls qdev_init_gpio_in() or
> qdev_init_gpio_in_named() for an example of inbound signals.
> Outbound signals might be created via qdev_init_gpio_out(),
> qdev_init_gpio_out_named() or sysbus_init_irq().

Not sure if this is a valid example, but when adding:

-- >8 --
diff --git a/hw/intc/ioapic.c b/hw/intc/ioapic.c
index bca71b5934b..b8b4ba362b1 100644
--- a/hw/intc/ioapic.c
+++ b/hw/intc/ioapic.c
@@ -96,6 +96,8 @@ static void ioapic_service(IOAPICCommonState *s)
     uint32_t mask;
     uint64_t entry;

+    assert(!resettable_is_in_reset(OBJECT(s)));
+
     for (i = 0; i < IOAPIC_NUM_PINS; i++) {
         mask = 1 << i;
         if (s->irr & mask) {
---

I get a MMIO write triggered from an IRQ:

(gdb) bt
#3  0x0000555558e44a12 in memory_region_write_accessor
(mr=0x61600001ab10, addr=0, value=0x7fffffffaa10, size=4, shift=0,
mask=4294967295, attrs=...) at softmmu/memory.c:482
#4  0x0000555558e4453b in access_with_adjusted_size (addr=0,
value=0x7fffffffaa10, size=4, access_size_min=1, access_size_max=4,
access_fn=
    0x555558e44600 <memory_region_write_accessor>, mr=0x61600001ab10,
attrs=...) at softmmu/memory.c:545
#5  0x0000555558e42c56 in memory_region_dispatch_write
(mr=0x61600001ab10, addr=0, data=0, op=MO_32, attrs=...) at
softmmu/memory.c:1466
#6  0x0000555558f322b3 in address_space_stl_internal (as=0x55555c0120e0
<address_space_memory>, addr=4276092928, val=0, attrs=..., result=0x0,
endian=DEVICE_LITTLE_ENDIAN)
    at memory_ldst.c.inc:315
#7  0x0000555558f32802 in address_space_stl_le (as=0x55555c0120e0
<address_space_memory>, addr=4276092928, val=0, attrs=..., result=0x0)
at memory_ldst.c.inc:353
#8  0x0000555558be2e22 in stl_le_phys (as=0x55555c0120e0
<address_space_memory>, addr=4276092928, val=0) at
/home/phil/source/qemu/include/exec/memory_ldst_phys.h.inc:103
#9  0x0000555558be0e14 in ioapic_service (s=0x61b000002a80) at
hw/intc/ioapic.c:138
#10 0x0000555558be4901 in ioapic_set_irq (opaque=0x61b000002a80,
vector=2, level=1) at hw/intc/ioapic.c:186
#11 0x00005555598769f6 in qemu_set_irq (irq=0x606000040f40, level=1) at
hw/core/irq.c:44
#12 0x00005555585fc097 in gsi_handler (opaque=0x61200000b8c0, n=0,
level=1) at hw/i386/x86.c:336
#13 0x00005555598769f6 in qemu_set_irq (irq=0x60600003db80, level=1) at
hw/core/irq.c:44
#14 0x0000555557653047 in hpet_handle_legacy_irq (opaque=0x61f000000080,
n=0, level=1) at hw/timer/hpet.c:707
#15 0x00005555598769f6 in qemu_set_irq (irq=0x606000042500, level=1) at
hw/core/irq.c:44
#16 0x00005555571c0686 in pit_irq_timer_update (s=0x616000032018,
current_time=0) at hw/timer/i8254.c:262
#17 0x00005555571c01c9 in pit_irq_control (opaque=0x616000031e80, n=0,
enable=1) at hw/timer/i8254.c:304
#18 0x00005555598769f6 in qemu_set_irq (irq=0x6060000435e0, level=1) at
hw/core/irq.c:44
#19 0x00005555576518cb in hpet_reset (d=0x61f000000080) at
hw/timer/hpet.c:690
#20 0x000055555986dfbe in device_transitional_reset (obj=0x61f000000080)
at hw/core/qdev.c:1114
#21 0x0000555559870e8e in resettable_phase_hold (obj=0x61f000000080,
opaque=0x0, type=RESET_TYPE_COLD) at hw/core/resettable.c:182
#22 0x0000555559846add in bus_reset_child_foreach (obj=0x60c00002e000,
cb=0x5555598707e0 <resettable_phase_hold>, opaque=0x0,
type=RESET_TYPE_COLD) at hw/core/bus.c:94
#23 0x0000555559873c29 in resettable_child_foreach (rc=0x60e00003e160,
obj=0x60c00002e000, cb=0x5555598707e0 <resettable_phase_hold>,
opaque=0x0, type=RESET_TYPE_COLD)
    at hw/core/resettable.c:96
#24 0x0000555559870b01 in resettable_phase_hold (obj=0x60c00002e000,
opaque=0x0, type=RESET_TYPE_COLD) at hw/core/resettable.c:173
#25 0x000055555986fbc3 in resettable_assert_reset (obj=0x60c00002e000,
type=RESET_TYPE_COLD) at hw/core/resettable.c:60
#26 0x000055555986fa6a in resettable_reset (obj=0x60c00002e000,
type=RESET_TYPE_COLD) at hw/core/resettable.c:45
#27 0x00005555598725ba in resettable_cold_reset_fn
(opaque=0x60c00002e000) at hw/core/resettable.c:269
#28 0x000055555986f9e9 in qemu_devices_reset () at hw/core/reset.c:69
#29 0x000055555865d711 in pc_machine_reset (machine=0x615000020100) at
hw/i386/pc.c:1901
#30 0x00005555589ea197 in qemu_system_reset (reason=SHUTDOWN_CAUSE_NONE)
at softmmu/vl.c:1403
#31 0x00005555589f7738 in qemu_init (argc=16, argv=0x7fffffffd278,
envp=0x7fffffffd300) at softmmu/vl.c:4458
#32 0x00005555571615fa in main (argc=16, argv=0x7fffffffd278,
envp=0x7fffffffd300) at softmmu/main.c:49