Re: [Qemu-devel] [PATCH] Add another sanity check to smp_parse() function

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Tue, 25 Aug 2015 15:25:00 +0200
Thomas Huth <thuth@redhat.com> wrote:

> On 19/08/15 17:58, Eduardo Habkost wrote:
> > On Wed, Jul 22, 2015 at 03:59:50PM +0200, Thomas Huth wrote:
> >> The code in smp_parse already checks the topology information for
> >> sockets * cores * threads < cpus and bails out with an error in
> >> that case. However, it is still possible to supply a bad configuration
> >> the other way round, e.g. with:
> >>
> >>  qemu-system-xxx -smp 4,sockets=1,cores=4,threads=2
> >>
> >> QEMU then still starts the guest, with topology configuration that
> >> is rather incomprehensible and likely not what the user wanted.
> >> So let's add another check to refuse such wrong configurations.
> >>
> >> Signed-off-by: Thomas Huth <thuth@redhat.com>
> >> ---
> >>  vl.c | 8 +++++++-
> >>  1 file changed, 7 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/vl.c b/vl.c
> >> index 5856396..c8d24b1 100644
> >> --- a/vl.c
> >> +++ b/vl.c
> >> @@ -1224,7 +1224,13 @@ static void smp_parse(QemuOpts *opts)
> >>              exit(1);
> >>          }
> >>  
> >> -        max_cpus = qemu_opt_get_number(opts, "maxcpus", 0);
> >> +        max_cpus = qemu_opt_get_number(opts, "maxcpus", cpus);
> >> +        if (sockets * cores * threads > max_cpus) {
> >> +            fprintf(stderr, "cpu topology: error: "
> >> +                    "sockets (%u) * cores (%u) * threads (%u) > maxcpus (%u)\n",
> >> +                    sockets, cores, threads, max_cpus);
> >> +            exit(1);
> >> +        }
> > 
> > I am always afraid of breaking existing setups when we do that, because
> > there may be existing VMs running with these weird configurations, and
> > people won't be able to live-migrate them to a newer QEMU.
> > 
> > But I think we really have to start refusing to run obviously broken
> > configurations one day, or we will never fix this mess, so:
> > 
> > Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
> > 
> > I want to apply this through the x86 tree, but I would like to get some
> > Acked-by from other maintainers first.
> 
> Ok, thanks!
> 
> So *ping* to the other CPU core maintainers here ... could I get some
> more ACKs, please?

Looks reasonable.

Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>