Re: [Qemu-devel] [PATCH] vl.c: make sure maxcpus matches topology to prevent migration failure

[Paolo Bonzini]

On 23/08/2018 16:51, Igor Mammedov wrote:
> Topology (threads*cores*sockets) must match maxcpus to be valid,
> otherwise we could start QEMU with invalid topology that throws
> a error on migration destination side, that should not be reachable:
> Source:
>   -smp 8,maxcpus=64,cores=1,threads=8,sockets=1
> // hotplug cpus upto maxcpus
> Destination:
>   -smp 64,maxcpus=64,cores=1,threads=8,sockets=1
>   qemu: cpu topology: sockets (1) * cores (1) * threads (8) < smp_cpus (64)

The destination should have sockets=8, shouldn't it?

It seems to me that, at startup, you should have cpus = s*t*c and cpus
<= maxcpus.  Currently we check cpus <= s*t*c <= maxcpus, which doesn't
make much sense.

Paolo

> Signed-off-by: Igor Mammedov <address@hidden>
> ---
>  vl.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/vl.c b/vl.c
> index 16b913f..2b35e0c 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -1238,10 +1238,10 @@ static void smp_parse(QemuOpts *opts)
>              exit(1);
>          }
>  
> -        if (sockets * cores * threads > max_cpus) {
> +        if (sockets * cores * threads != max_cpus) {
>              error_report("cpu topology: "
> -                         "sockets (%u) * cores (%u) * threads (%u) > "
> -                         "maxcpus (%u)",
> +                         "sockets (%u) * cores (%u) * threads (%u) not equal 
> to"
> +                         " maxcpus (%u)",
>                           sockets, cores, threads, max_cpus);
>              exit(1);
>          }
>