Re: [Patch v1] x86: Fix the logical destination mode test

Vitaly Kuznetsov
2020-04-14T14:01:21Z

Nitesh Narayan Lal <nitesh@redhat.com> writes:

> On 3/10/20 10:03 AM, Marcelo Tosatti wrote:
>> On Mon, Mar 09, 2020 at 07:15:50PM -0400, Nitesh Narayan Lal wrote:
>>> There are following issues with the ioapic logical destination mode test:
>>>
>>> - A race condition that is triggered when the interrupt handler
>>>   ioapic_isr_86() is called at the same time by multiple vCPUs. Due to this
>>> the g_isr_86 is not correctly incremented. To prevent this a spinlock is
>>> added around ‘g_isr_86++’.
>>>
>>> - On older QEMU versions initial x2APIC ID is not set, that is why
>>>   the local APIC IDs of each vCPUs are not configured. Hence the logical
>>>   destination mode test fails/hangs. Adding ‘+x2apic’ to the qemu -cpu params
>>>   ensures that the local APICs are configured every time, irrespective of the
>>>   QEMU version.
>>>
>>> - With ‘-machine kernel_irqchip=split’ included in the ioapic test
>>>   test_ioapic_self_reconfigure() always fails and somehow leads to a state where
>>>   after submitting IOAPIC fixed delivery - logical destination mode request we
>>>   never receive an interrupt back. For now, the physical and logical destination
>>>   mode tests are moved above test_ioapic_self_reconfigure().
>>>
>>> Fixes: b2a1ee7e ("kvm-unit-test: x86: ioapic: Test physical and logical destination mode")
>>> Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
>> Looks good to me.
>
> Hi,
>
> I just wanted to follow up and see if there are any more suggestions for me to
> improve this patch before it can be merged.
>
>
>>
>>> ---
>>> x86/ioapic.c | 11 +++++++----
>>> x86/unittests.cfg | 2 +-
>>> 2 files changed, 8 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/x86/ioapic.c b/x86/ioapic.c
>>> index 742c711..3106531 100644
>>> --- a/x86/ioapic.c
>>> +++ b/x86/ioapic.c
>>> @@ -432,10 +432,13 @@ static void test_ioapic_physical_destination_mode(void)
>>> }
>>>
>>> static volatile int g_isr_86;
>>> +struct spinlock ioapic_lock;
>>>
>>> static void ioapic_isr_86(isr_regs_t *regs)
>>> {
>>> + spin_lock(&ioapic_lock);
>>> ++g_isr_86;
>>> + spin_unlock(&ioapic_lock);
>>> set_irq_line(0x0e, 0);
>>> eoi();
>>> }
>>> @@ -501,6 +504,10 @@ int main(void)
>>> test_ioapic_level_tmr(true);
>>> test_ioapic_edge_tmr(true);
>>>
>>> + test_ioapic_physical_destination_mode();

I just found out that this particular change causes 'ioapic-split' test
to hang reliably:

# ./run_tests.sh ioapic-split
FAIL ioapic-split (timeout; duration=90s)
PASS ioapic (26 tests)

unlike 'ioapic' test we run it with '-smp 1' and
'test_ioapic_physical_destination_mode' requires > 1 CPU to work AFAICT.

Why do we move it from under 'if (cpu_count() > 1)' ?

Also, this patch could've been split.

>>> + if (cpu_count() > 3)
>>> + test_ioapic_logical_destination_mode();
>>> +
>>> if (cpu_count() > 1) {
>>> test_ioapic_edge_tmr_smp(false);
>>> test_ioapic_level_tmr_smp(false);
>>> @@ -508,11 +515,7 @@ int main(void)
>>> test_ioapic_edge_tmr_smp(true);
>>>
>>> test_ioapic_self_reconfigure();
>>> - test_ioapic_physical_destination_mode();
>>> }
>>>
>>> - if (cpu_count() > 3)
>>> - test_ioapic_logical_destination_mode();
>>> -
>>> return report_summary();
>>> }
>>> diff --git a/x86/unittests.cfg b/x86/unittests.cfg
>>> index f2401eb..d658bc8 100644
>>> --- a/x86/unittests.cfg
>>> +++ b/x86/unittests.cfg
>>> @@ -46,7 +46,7 @@ timeout = 30
>>> [ioapic]
>>> file = ioapic.flat
>>> smp = 4
>>> -extra_params = -cpu qemu64
>>> +extra_params = -cpu qemu64,+x2apic
>>> arch = x86_64
>>>
>>> [cmpxchg8b]
>>> --
>>> 1.8.3.1

--
Vitaly