Re: [PATCH v2 ppc-for-5.0 2/2] ppc/spapr: Support reboot of secure pseries guest

[Greg Kurz <groug@kaod.org>]

On Thu, 12 Dec 2019 14:23:43 +0530
Bharata B Rao <bharata@linux.ibm.com> wrote:

> On Thu, Dec 12, 2019 at 08:34:57AM +0100, Cédric Le Goater wrote:
> > Hello Bharata,
> > 
> > 
> > On 12/12/2019 06:50, Bharata B Rao wrote:
> > > A pseries guest can be run as a secure guest on Ultravisor-enabled
> > > POWER platforms. When such a secure guest is reset, we need to
> > > release/reset a few resources both on ultravisor and hypervisor side.
> > > This is achieved by invoking this new ioctl KVM_PPC_SVM_OFF from the
> > > machine reset path.
> > > 
> > > As part of this ioctl, the secure guest is essentially transitioned
> > > back to normal mode so that it can reboot like a regular guest and
> > > become secure again.
> > > 
> > > This ioctl has no effect when invoked for a normal guest. If this ioctl
> > > fails for a secure guest, the guest is terminated.
> > 
> > This looks OK. 
> > 
> > > Signed-off-by: Bharata B Rao <bharata@linux.ibm.com>
> > > ---
> > >  hw/ppc/spapr.c       | 15 +++++++++++++++
> > >  target/ppc/kvm.c     |  7 +++++++
> > >  target/ppc/kvm_ppc.h |  6 ++++++
> > >  3 files changed, 28 insertions(+)
> > > 
> > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > > index f11422fc41..25e1a3446e 100644
> > > --- a/hw/ppc/spapr.c
> > > +++ b/hw/ppc/spapr.c
> > > @@ -1597,6 +1597,21 @@ static void spapr_machine_reset(MachineState *machine)
> > >      void *fdt;
> > >      int rc;
> > >  
> > > +    /*
> > > +     * KVM_PPC_SVM_OFF ioctl can fail for secure guests, check and
> > > +     * exit in that case. However check for -ENOTTY explicitly
> > > +     * to ensure that we don't terminate normal guests that are
> > > +     * running on kernels which don't support this ioctl.
> > > +     *
> > > +     * Also, this ioctl returns 0 for normal guests on kernels where
> > > +     * this ioctl is supported.
> > > +     */
> > > +    rc = kvmppc_svm_off();
> > > +    if (rc && rc != -ENOTTY) {
> > 
> > I would put these low level tests under kvmppc_svm_off().
> 
> Makes sense.
> 
> > 
> > > +        error_report("Reset of secure guest failed, exiting...");
> > > +        exit(EXIT_FAILURE);
> > 
> > The exit() could probably go under kvmppc_svm_off() also.
> 
> May be not. Then error_report would have also have to go in.
> Doesn't make sense to print this error from there.
> 

Why doesn't it make sense ? It seems there's a consensus that the
failure (at least the -EINVAL case) isn't recoverable in any way.
Are there cases where we would call this and the caller could
cope with an error ?

> Regards,
> Bharata.
> 
>