Re: Crash when using cpupools

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

HI Juergen,

> On 6 Sep 2021, at 10:28, Juergen Gross <jgross@xxxxxxxx> wrote:
> 
> On 06.09.21 10:46, Andrew Cooper wrote:
>> On 06/09/2021 09:23, Juergen Gross wrote:
>>> On 03.09.21 17:41, Bertrand Marquis wrote:
>>>> Hi,
>>>> 
>>>> While doing some investigation with cpupools I encountered a crash
>>>> when trying to isolate a guest to its own physical cpu.
>>>> 
>>>> I am using current staging status.
>>>> 
>>>> I did the following (on FVP with 8 cores):
>>>> - start dom0 with dom0_max_vcpus=1
>>>> - remove core 1 from dom0 cpupool: xl cpupool-cpu-remove Pool-0 1
>>>> - create a new pool: xl cpupool-create name=\"NetPool\”
>>>> - add core 1 to the pool: xl cpupool-cpu-add NetPool 1
>>>> - create a guest in NetPool using the following in the guest config:
>>>> pool=“NetPool"
>>>> 
>>>> I end with a crash with the following call trace during guest creation:
>>>> (XEN) Xen call trace:
>>>> (XEN)    [<0000000000234cb0>] credit2.c#csched2_alloc_udata+0x58/0xfc
>>>> (PC)
>>>> (XEN)    [<0000000000234c80>] credit2.c#csched2_alloc_udata+0x28/0xfc
>>>> (LR)
>>>> (XEN)    [<0000000000242d38>] sched_move_domain+0x144/0x6c0
>>>> (XEN)    [<000000000022dd18>]
>>>> cpupool.c#cpupool_move_domain_locked+0x38/0x70
>>>> (XEN)    [<000000000022fadc>] cpupool_do_sysctl+0x73c/0x780
>>>> (XEN)    [<000000000022d8e0>] do_sysctl+0x788/0xa58
>>>> (XEN)    [<0000000000273b68>] traps.c#do_trap_hypercall+0x78/0x170
>>>> (XEN)    [<0000000000274f70>] do_trap_guest_sync+0x138/0x618
>>>> (XEN)    [<0000000000260458>] entry.o#guest_sync_slowpath+0xa4/0xd4
>>>> 
>>>> After some debugging I found out that unit->vcpu_list is NULL after
>>>> unit->vcpu_list = d->vcpu[unit->unit_id]; with unit_id 0 in
>>>> common/sched/core.c:688
>>>> This makes the call to is_idle_unit(unit) in csched2_alloc_udata
>>>> trigger the crash.
>>> 
>>> So there is no vcpu 0 in that domain? How is this possible?
>> Easy, depending on the order of hypercalls issued by the toolstack.
>> Between DOMCTL_createdomain and DOMCTL_max_vcpus, the domain exists but
>> the vcpus haven't been allocated.
> 
> Oh yes, indeed.
> 
> Bertrand, does the attached patch fix the issue for you?

It does, my guest is now booting properly :-)
So this is solving the issue on arm (and probably on x86 if it was present but 
untested by me).

Feel free to add to your patch my:
Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>

Thanks a lot for the quick fix
Cheers
Bertrand

> 
> 
> Juergen
> <0001-xen-sched-fix-sched_move_domain-for-domain-without-v.patch><OpenPGP_0xB0DE9DD628BF132F.asc>