On 11/23/21 3:50 PM, Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
wrote:
>
>
>> -----Original Message-----
>> From: Dongli Zhang [mailto:[email protected]]
>> Sent: Wednesday, November 24, 2021 5:22 AM
>> To: Sebastian Andrzej Siewior <[email protected]>; Longpeng (Mike, Cloud
>> Infrastructure Service Product Dept.) <[email protected]>
>> Cc: [email protected]; Gonglei (Arei) <[email protected]>;
>> [email protected]; [email protected]; Peter Zijlstra
>> <[email protected]>; Ingo Molnar <[email protected]>; Valentin Schneider
>> <[email protected]>; Boris Ostrovsky <[email protected]>;
>> Juergen Gross <[email protected]>; Stefano Stabellini <[email protected]>;
>> Thomas Gleixner <[email protected]>; Ingo Molnar <[email protected]>;
>> Borislav
>> Petkov <[email protected]>; Dave Hansen <[email protected]>; H. Peter
>> Anvin <[email protected]>
>> Subject: Re: [PATCH] cpu/hotplug: Allow the CPU in CPU_UP_PREPARE state to be
>> brought up again.
>>
>> Tested-by: Dongli Zhang <[email protected]>
>>
>>
>> The bug fixed by commit 53fafdbb8b21 ("KVM: x86: switch KVMCLOCK base to
>> monotonic raw clock") may leave the cpu_hotplug_state at CPU_UP_PREPARE. As a
>> result, to online this CPU again (even after removal) is always failed.
>>
>> I have tested that this patch works well to workaround the issue, by
>> introducing
>> either a mdeley(11000) or while(1); to start_secondary(). That is, to online
>> the
>> same CPU again is successful even after initial do_boot_cpu() failure.
>>
>> 1. add mdelay(11000) or while(1); to the start_secondary().
>>
>> 2. to online CPU is failed at do_boot_cpu().
>>
>
> Thanks for your testing :)
>
> Does the cpu4 spin in wait_for_master_cpu() in your case ?
I did two tests.
TEST 1.
I added "mdelay(11000);" as the first line in start_secondary(). Once the issue
was encountered, the RIP of CPU=4 was ffffffff8c242021 (from QEMU's "info
registers -a") which was in the range of wait_for_master_cpu().
# cat /proc/kallsyms | grep ffffffff8c2420
ffffffff8c242010 t wait_for_master_cpu
ffffffff8c242030 T load_fixmap_gdt
ffffffff8c242060 T native_write_cr4
ffffffff8c2420c0 T cr4_init
TEST 2.
I added "while(true);" as the first line in start_secondary(). Once the issue
was encountered, the RIP of CPU=4 was ffffffff91654c0a (from QEMU's "info
registers -a") which was in the range of start_secondary().
# cat /proc/kallsyms | grep ffffffff91654c0
ffffffff91654c00 t start_secondary
Dongli Zhang
>
>> 3. to online CPU again is failed without this patch.
>>
>> # echo 1 > /sys/devices/system/cpu/cpu4/online
>> -su: echo: write error: Input/output error
>>
>> 4. to online CPU again is successful with this patch.
>>
>> Thank you very much!
>>
>> Dongli Zhang
>>
>> On 11/22/21 7:47 AM, Sebastian Andrzej Siewior wrote:
>>> From: "Longpeng(Mike)" <[email protected]>
>>>
>>> A CPU will not show up in virtualized environment which includes an
>>> Enclave. The VM splits its resources into a primary VM and a Enclave
>>> VM. While the Enclave is active, the hypervisor will ignore all requests
>>> to bring up a CPU and this CPU will remain in CPU_UP_PREPARE state.
>>> The kernel will wait up to ten seconds for CPU to show up
>>> (do_boot_cpu()) and then rollback the hotplug state back to
>>> CPUHP_OFFLINE leaving the CPU state in CPU_UP_PREPARE. The CPU state is
>>> set back to CPUHP_TEARDOWN_CPU during the CPU_POST_DEAD stage.
>>>
>>> After the Enclave VM terminates, the primary VM can bring up the CPU
>>> again.
>>>
>>> Allow to bring up the CPU if it is in the CPU_UP_PREPARE state.
>>>
>>> [bigeasy: Rewrite commit description.]
>>>
>>> Signed-off-by: Longpeng(Mike) <[email protected]>
>>> Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
>>> Link:
>> https://urldefense.com/v3/__https://lore.kernel.org/r/20210901051143.2752-1
>> [email protected]__;!!ACWV5N9M2RV99hQ!d4sCCXMQV7ekFwpd21vo1_9K-m5h4VZ-g
>> E8Z62PLL58DT4VJ6StH57TR_KpBdbwhBE0$
>>> ---
>>>
>>> For XEN: this changes the behaviour as it allows to invoke
>>> cpu_initialize_context() again should it have have earlier. I *think*
>>> this is okay and would to bring up the CPU again should the memory
>>> allocation in cpu_initialize_context() fail.
>>>
>>> kernel/smpboot.c | 7 +++++++
>>> 1 file changed, 7 insertions(+)
>>>
>>> diff --git a/kernel/smpboot.c b/kernel/smpboot.c
>>> index f6bc0bc8a2aab..34958d7fe2c1c 100644
>>> --- a/kernel/smpboot.c
>>> +++ b/kernel/smpboot.c
>>> @@ -392,6 +392,13 @@ int cpu_check_up_prepare(int cpu)
>>> */
>>> return -EAGAIN;
>>>
>>> + case CPU_UP_PREPARE:
>>> + /*
>>> + * Timeout while waiting for the CPU to show up. Allow to try
>>> + * again later.
>>> + */
>>> + return 0;
>>> +
>>> default:
>>>
>>> /* Should not happen. Famous last words. */
>>>
