> On 1 Apr 2019, at 16:36, Vitaly Kuznetsov <vkuzn...@redhat.com> wrote:
>
> It was found that Hyper-V 2016 on KVM in some configurations (q35 machine +
> piix4-usb-uhci) hangs on boot. Trace analysis led us to the conclusion that
> it is mishandling level-triggered interrupt performing EOI without fixing
> the root cause.
I would rephrase as:
It was found that Hyper-V 2016 on KVM in some configurations (q35 machine +
piix4-usb-uhci) hangs on boot.
Root-cause was that one of Hyper-V level-triggered interrupt handler performs
EOI before fixing the root-cause.
This results in IOAPIC keep re-raising the level-triggered interrupt after EOI
because irq-line remains asserted.
> This causes immediate re-assertion and L2 VM (which is
> supposedly expected to fix the cause of the interrupt) is not making any
> progress.
I don’t know why you assume this.
From the trace we have examined, it seems that the EOI is performed by Hyper-V
and not it’s guest
This means that the handler for this level-triggered interrupt is on Hyper-V
and not it’s guest.
>
> Gory details:
> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.spinics.net_lists_kvm_msg184484.html&d=DwIDAg&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=Q0Ico0Nb_DGRDrDgXkjkRr-xjzIbOLteVOhDJXBD_pU&s=d_H4_-qzqGvyi8X7g_KA0hZ5a8zjfHQhe1BhLPIokcA&e=
Maybe worth to note that one should read the entire thread to understand the
analysis.
>
> Turns out we were dealing with similar issues before; in-kernel IOAPIC
> implementation has commit 184564efae4d ("kvm: ioapic: conditionally delay
> irq delivery duringeoi broadcast") which describes a very similar issue.
>
> Steal the idea from the above mentioned commit for IOAPIC implementation in
> QEMU. SUCCESSIVE_IRQ_MAX_COUNT, delay and the comment are borrowed as well.
>
> Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com>
> ---
> hw/intc/ioapic.c | 43 ++++++++++++++++++++++++++++++-
> hw/intc/trace-events | 1 +
> include/hw/i386/ioapic_internal.h | 3 +++
> 3 files changed, 46 insertions(+), 1 deletion(-)
>
> diff --git a/hw/intc/ioapic.c b/hw/intc/ioapic.c
> index 9d75f84d3b..daf45cc8a8 100644
> --- a/hw/intc/ioapic.c
> +++ b/hw/intc/ioapic.c
> @@ -139,6 +139,15 @@ static void ioapic_service(IOAPICCommonState *s)
> }
> }
>
> +#define SUCCESSIVE_IRQ_MAX_COUNT 10000
> +
> +static void ioapic_timer(void *opaque)
> +{
> + IOAPICCommonState *s = opaque;
> +
> + ioapic_service(s);
> +}
> +
> static void ioapic_set_irq(void *opaque, int vector, int level)
> {
> IOAPICCommonState *s = opaque;
> @@ -227,7 +236,28 @@ void ioapic_eoi_broadcast(int vector)
> trace_ioapic_clear_remote_irr(n, vector);
> s->ioredtbl[n] = entry & ~IOAPIC_LVT_REMOTE_IRR;
This clear of remote-irr should happen only for level-triggered interrupts.
So we can make the code here more structured like KVM’s
__kvm_ioapic_update_eoi().
It also have an extra-value of not advancing "s->irq_reassert[vector]” for
vectors which are edge-triggered which is a bit misleading.
> if (!(entry & IOAPIC_LVT_MASKED) && (s->irr & (1 << n))) {
> - ioapic_service(s);
> + bool level = ((entry >> IOAPIC_LVT_TRIGGER_MODE_SHIFT) &
> 1)
> + == IOAPIC_TRIGGER_LEVEL;
Nit: I would declare variable “trig_mode” and compare it later explicitly to
IOAPIC_TRIGGER_LEVEL.
> +
> + ++s->irq_reassert[vector];
Nit: I would rename “irq_reassert” to “irq_eoi” as it is named in KVM IOAPIC
code.
> + if (!level ||
> + s->irq_reassert[vector] < SUCCESSIVE_IRQ_MAX_COUNT) {
> + ioapic_service(s);
> + } else {
> + /*
> + * Real hardware does not deliver the interrupt
> + * immediately during eoi broadcast, and this lets a
> + * buggy guest make slow progress even if it does not
> + * correctly handle a level-triggered interrupt.
> Emulate
> + * this behavior if we detect an interrupt storm.
> + */
> + trace_ioapic_eoi_delayed_reassert(vector);
> + timer_mod(s->timer,
> + qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
> + NANOSECONDS_PER_SECOND / 100);
You need to zero here s->irq_reassert[vector].
I think you would avoid these kind of little mistakes if you will attempt to
follow KVM’s commit code structure.
> + }
> + } else {
> + s->irq_reassert[vector] = 0;
> }
> }
> }
> @@ -401,6 +431,8 @@ static void ioapic_realize(DeviceState *dev, Error **errp)
> memory_region_init_io(&s->io_memory, OBJECT(s), &ioapic_io_ops, s,
> "ioapic", 0x1000);
>
> + s->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, ioapic_timer, s);
> +
> qdev_init_gpio_in(dev, ioapic_set_irq, IOAPIC_NUM_PINS);
>
> ioapics[ioapic_no] = s;
> @@ -408,6 +440,14 @@ static void ioapic_realize(DeviceState *dev, Error
> **errp)
> qemu_add_machine_init_done_notifier(&s->machine_done);
> }
>
> +static void ioapic_unrealize(DeviceState *dev, Error **errp)
> +{
> + IOAPICCommonState *s = IOAPIC_COMMON(dev);
> +
> + timer_del(s->timer);
> + timer_free(s->timer);
> +}
> +
> static Property ioapic_properties[] = {
> DEFINE_PROP_UINT8("version", IOAPICCommonState, version, IOAPIC_VER_DEF),
> DEFINE_PROP_END_OF_LIST(),
> @@ -419,6 +459,7 @@ static void ioapic_class_init(ObjectClass *klass, void
> *data)
> DeviceClass *dc = DEVICE_CLASS(klass);
>
> k->realize = ioapic_realize;
> + k->unrealize = ioapic_unrealize;
> /*
> * If APIC is in kernel, we need to update the kernel cache after
> * migration, otherwise first 24 gsi routes will be invalid.
> diff --git a/hw/intc/trace-events b/hw/intc/trace-events
> index a28bdce925..90c9d07c1a 100644
> --- a/hw/intc/trace-events
> +++ b/hw/intc/trace-events
> @@ -25,6 +25,7 @@ apic_mem_writel(uint64_t addr, uint32_t val) "0x%"PRIx64" =
> 0x%08x"
> ioapic_set_remote_irr(int n) "set remote irr for pin %d"
> ioapic_clear_remote_irr(int n, int vector) "clear remote irr for pin %d
> vector %d"
> ioapic_eoi_broadcast(int vector) "EOI broadcast for vector %d"
> +ioapic_eoi_delayed_reassert(int vector) "delayed reassert on EOI broadcast
> for vector %d"
> ioapic_mem_read(uint8_t addr, uint8_t regsel, uint8_t size, uint32_t val)
> "ioapic mem read addr 0x%"PRIx8" regsel: 0x%"PRIx8" size 0x%"PRIx8" retval
> 0x%"PRIx32
> ioapic_mem_write(uint8_t addr, uint8_t regsel, uint8_t size, uint32_t val)
> "ioapic mem write addr 0x%"PRIx8" regsel: 0x%"PRIx8" size 0x%"PRIx8" val
> 0x%"PRIx32
> ioapic_set_irq(int vector, int level) "vector: %d level: %d"
> diff --git a/include/hw/i386/ioapic_internal.h
> b/include/hw/i386/ioapic_internal.h
> index 9848f391bb..e0ee88db40 100644
> --- a/include/hw/i386/ioapic_internal.h
> +++ b/include/hw/i386/ioapic_internal.h
> @@ -96,6 +96,7 @@ typedef struct IOAPICCommonClass {
> SysBusDeviceClass parent_class;
>
> DeviceRealize realize;
> + DeviceUnrealize unrealize;
> void (*pre_save)(IOAPICCommonState *s);
> void (*post_load)(IOAPICCommonState *s);
> } IOAPICCommonClass;
> @@ -111,6 +112,8 @@ struct IOAPICCommonState {
> uint8_t version;
> uint64_t irq_count[IOAPIC_NUM_PINS];
> int irq_level[IOAPIC_NUM_PINS];
> + int irq_reassert[IOAPIC_NUM_PINS];
> + QEMUTimer *timer;
> };
>
> void ioapic_reset_common(DeviceState *dev);
> --
> 2.20.1
>