Re: [PATCH v2 04/10] Introduce the CPU address space destruction function

[David Hildenbrand <david@redhat.com>]

On 26.09.23 14:32, Salil Mehta wrote:
>> From: David Hildenbrand <david@redhat.com>
>> Sent: Tuesday, September 26, 2023 1:24 PM
>>
>> On 26.09.23 13:55, Salil Mehta wrote:
>>>> From: Salil Mehta
>>>> Sent: Tuesday, September 26, 2023 12:21 PM
>>>> To: 'David Hildenbrand' <david@redhat.com>; lixianglai
>>>> <lixianglai@loongson.cn>; qemu-devel@nongnu.org
>>>> Cc: Salil Mehta <salil.mehta@opnsrc.net>; Xiaojuan Yang
>>>> <yangxiaojuan@loongson.cn>; Song Gao <gaosong@loongson.cn>; Michael S.
>>>> Tsirkin <mst@redhat.com>; Igor Mammedov <imammedo@redhat.com>; Ani Sinha
>>>> <anisinha@redhat.com>; Paolo Bonzini <pbonzini@redhat.com>; Richard
>>>> Henderson <richard.henderson@linaro.org>; Eduardo Habkost
>>>> <eduardo@habkost.net>; Marcel Apfelbaum <marcel.apfelbaum@gmail.com>;
>>>> Philippe Mathieu-Daudé <philmd@linaro.org>; wangyanan (Y)
>>>> <wangyanan55@huawei.com>; Daniel P. Berrangé <berrange@redhat.com>;
>> Peter
>>>> Xu <peterx@redhat.com>; Bibo Mao <maobibo@loongson.cn>
>>>> Subject: RE: [PATCH v2 04/10] Introduce the CPU address space
>> destruction
>>>> function
>>>>
>>>> Hi David,
>>>>
>>>>> From: David Hildenbrand <david@redhat.com>
>>>>> Sent: Friday, September 15, 2023 9:07 AM
>>>>> To: lixianglai <lixianglai@loongson.cn>; qemu-devel@nongnu.org; Salil
>>>> Mehta
>>>>> <salil.mehta@huawei.com>
>>>>> Cc: Salil Mehta <salil.mehta@opnsrc.net>; Xiaojuan Yang
>>>>> <yangxiaojuan@loongson.cn>; Song Gao <gaosong@loongson.cn>; Michael S.
>>>>> Tsirkin <mst@redhat.com>; Igor Mammedov <imammedo@redhat.com>; Ani
>> Sinha
>>>>> <anisinha@redhat.com>; Paolo Bonzini <pbonzini@redhat.com>; Richard
>>>>> Henderson <richard.henderson@linaro.org>; Eduardo Habkost
>>>>> <eduardo@habkost.net>; Marcel Apfelbaum <marcel.apfelbaum@gmail.com>;
>>>>> Philippe Mathieu-Daudé <philmd@linaro.org>; wangyanan (Y)
>>>>> <wangyanan55@huawei.com>; Daniel P. Berrangé <berrange@redhat.com>;
>> Peter
>>>>> Xu <peterx@redhat.com>; Bibo Mao <maobibo@loongson.cn>
>>>>> Subject: Re: [PATCH v2 04/10] Introduce the CPU address space
>> destruction
>>>>> function
>>>>>
>>>>> On 15.09.23 04:53, lixianglai wrote:
>>>>>> Hi David Hildenbrand:
>>>>>>
>>>>>>>
>>>>>>> Hi David Hildenbrand:
>>>>>>>> On 14.09.23 15:00, lixianglai wrote:
>>>>>>>>> Hi David:
>>>>>>>>
>>>>>>>> Hi!
>>>>>>>>
>>>>>>>>>
>>>>>>>>>> On 12.09.23 04:11, xianglai li wrote:
>>>>>>>>>>> Introduce new function to destroy CPU address space resources
>>>>>>>>>>> for cpu hot-(un)plug.
>>>>>>>>>>>
>>>>>>>>>> How do other archs handle that? Or how are they able to get away
>>>>>>>>>> without destroying?
>>>>>>>>>>
>>>>>>>>> They do not remove the cpu address space, taking the X86
>>>>>>>>> architecture as
>>>>>>>>> an example:
>>>>>>>>>
>>>>>>>>> 1.Start the x86 VM:
>>>>>>>>>
>>>>>>>>> ./qemu-system-x86_64 \
>>>>>>>>> -machine q35  \
>>>>>>>>> -cpu Broadwell-IBRS \
>>>>>>>>> -smp 1,maxcpus=100,sockets=100,cores=1,threads=1 \
>>>>>>>>> -m 4G \
>>>>>>>>> -drive file=~/anolis-8.8.qcow2  \
>>>>>>>>> -serial stdio   \
>>>>>>>>> -monitor telnet:localhost:4498,server,nowait   \
>>>>>>>>> -nographic
>>>>>>>>>
>>>>>>>>> 2.Connect the qemu monitor
>>>>>>>>>
>>>>>>>>> telnet 127.0.0.1 4498
>>>>>>>>>
>>>>>>>>> info mtree
>>>>>>>>>
>>>>>>>>> address-space: cpu-memory-0
>>>>>>>>> address-space: memory
>>>>>>>>>        0000000000000000-ffffffffffffffff (prio 0, i/o): system
>>>>>>>>>          0000000000000000-000000007fffffff (prio 0, ram): alias
>>>>>>>>> ram-below-4g
>>>>>>>>> @pc.ram 0000000000000000-000000007fffffff
>>>>>>>>>          0000000000000000-ffffffffffffffff (prio -1, i/o): pci
>>>>>>>>>            00000000000a0000-00000000000bffff (prio 1, i/o): vga-
>> lowmem
>>>>>>>>>
>>>>>>>>> 3.Perform cpu hot swap int qemu monitor
>>>>>>>>>
>>>>>>>>> device_add
>>>>>>>>> Broadwell-IBRS-x86_64-cpu,socket-id=1,core-id=0,thread-id=0,id=cpu1
>>>>>>>>> device_del cpu1
>>>>>>>>>
>>>>>>>>
>>>>>>>> Hm, doesn't seem to work for me on upstream QEMU for some reason:
>>>>>>>> "Error: acpi: device unplug request for not supported device type:
>>>>>>>> Broadwell-IBRS-x86_64-cpu"
>>>>>>>
>>>>>> First I use qemu tcg, and then the cpu needs to be removed after the
>>>>>> operating system is booted.
>>>>>
>>>>> Ah, the last thing is the important bit. I can reproduce this with KVM
>>>>> easily.
>>>>>
>>>>> Doing it a couple of times
>>>>>
>>>>> address-space: cpu-memory-0
>>>>> address-space: cpu-memory-1
>>>>> address-space: cpu-memory-1
>>>>> address-space: cpu-memory-1
>>>>> address-space: cpu-memory-1
>>>>> address-space: cpu-memory-1
>>>>> address-space: cpu-memory-1
>>>>> address-space: cpu-memory-1
>>>>> address-space: cpu-memory-1
>>>>> address-space: cpu-memory-1
>>>>> address-space: cpu-memory-1
>>>>> address-space: cpu-memory-1
>>>>> address-space: cpu-memory-1
>>>>> address-space: cpu-memory-1
>>>>> address-space: cpu-memory-1
>>>>> address-space: cpu-memory-1
>>>>> address-space: cpu-memory-1
>>>>> address-space: cpu-memory-1
>>>>> address-space: cpu-memory-1
>>>>> address-space: cpu-memory-1
>>>>>
>>>>> Looks like a resource/memory leak.
>>>>
>>>> Yes, there was. Thanks for identifying it. I have fixed in the
>>>> latest RFC V2. Please check here:
>>>>
>>>> https://lore.kernel.org/qemu-devel/20230926100436.28284-1-
>>>> salil.mehta@huawei.com/T/#m5f5ae40b091d69d01012880d7500d96874a9d39c
>>>>
>>>> I have tested and AddressSpace comes and goes away cleanly
>>>> on CPU hot(un)plug action.
>>>
>>> Hi David/Xianglai,
>>> Are you okay if I put Reported-by and give reference to this
>>> conversation?
>>
>> Yes. And ideally, send the fixes separately from the other arm patches.
> 
> ARM Virtual CPU Hotplug support patches are still under review.

The other architectures (as shown, x86 is affected) can be fixed 
independent of that support.

-- 
Cheers,

David / dhildenb