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

[Salil Mehta]

> From: qemu-devel-bounces+salil.mehta=huawei.com@nongnu.org <qemu-devel-
> bounces+salil.mehta=huawei.com@nongnu.org> On Behalf Of lixianglai
> Sent: Thursday, September 14, 2023 2:01 PM
> To: David Hildenbrand <david@redhat.com>; 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:
> 
> > 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
> 
> info mtree
> 
> address-space: cpu-memory-0
> address-space: cpu-memory-1
> 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
> 
> 
>  From the above test, you can see whether the address space of cpu1 is
> residual after a cpu hot swap, and whether it is reasonable?
> 
> The address space destruction function of the CPU can be used to delete
> the residual address space of the CPU1.

Yes, it can be but I would interested to know if there is any problem
which might have gone unnoticed while doing it.

Many thanks
Salil.