Re: [Qemu-devel] [PATCH v6 01/11] machine: Don't allow CPU toplogies with partially filled cores

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

On Sat, Jan 23, 2016 at 11:47:22AM -0200, Eduardo Habkost wrote:
> On Fri, Jan 08, 2016 at 12:25:09PM +0530, Bharata B Rao wrote:
> > Prevent guests from booting with CPU topologies that have partially
> > filled CPU cores or can result in partially filled CPU cores after
> > CPU hotplug like
> > 
> > -smp 15,sockets=1,cores=4,threads=4,maxcpus=16 or
> > -smp 15,sockets=1,cores=4,threads=4,maxcpus=17.
> > 
> > This is enforced by introducing MachineClass::validate_smp_config()
> > that gets called from generic SMP parsing code. Machine type versions
> > that don't want to enforce this can override this method.
> > 
> > TODO: Only sPAPR and PC changes are done in this patch, other archs
> > will be touched after there is agreement on this approach.
> > 
> > Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> > ---
> >  hw/core/machine.c   | 20 ++++++++++++++++++++
> >  hw/i386/pc_piix.c   |  7 +++++++
> >  hw/i386/pc_q35.c    |  7 +++++++
> >  hw/ppc/spapr.c      |  7 +++++++
> >  include/hw/boards.h |  1 +
> >  vl.c                |  4 ++++
> >  6 files changed, 46 insertions(+)
> > 
> > diff --git a/hw/core/machine.c b/hw/core/machine.c
> > index c46ddc7..b66c101 100644
> > --- a/hw/core/machine.c
> > +++ b/hw/core/machine.c
> > @@ -336,6 +336,25 @@ static void machine_init_notify(Notifier *notifier, void *data)
> >      foreach_dynamic_sysbus_device(error_on_sysbus_device, NULL);
> >  }
> >  
> > +static int validate_smp_config_generic(int smp_cpus, int max_cpus,
> > +                                       int smp_threads)
> 
> Please make it use a Error** parameter to return error
> information, and let the caller decide what to do with the error
> message. One day the mc->validate_smp_config() call may be moved
> inside a function that returns error information using Error**
> and needs to propagate it to the caller.

Sure, will make this change.

I see that not all target archs use machine type versions and even
if they do it will not be a one-line changer (as shown for i386 and sPAPR in
this patch) for them to override mc->validate_smp_config() for older
versions.

So am I expected to change .class_init routine for all these archs by
setting mc->validate_smp_config() to a NOP validate_smp_config()
so that the default validate_smp_config() defined for TYPE_MACHINE
is overridden ? In order to preserve the existing behaviour with
CPU topology for all args, it appears that such a change would be
necessary, but I am not sure how to test all of them. Will just a compile
test do ?

Regards,
Bharata.