Re: [Qemu-ppc] [PATCH for-2.5 1/1] spapr: Handle failure of KVM_PPC_ALLOCATE_HTAB ioctl

[David Gibson]

On Mon, Nov 09, 2015 at 03:24:15PM +1100, David Gibson wrote:
> On Tue, Nov 03, 2015 at 03:38:19PM +0530, Bharata B Rao wrote:
> > KVM_PPC_ALLOCATE_HTAB ioctl can return -ENOMEM for KVM guests and QEMU
> > never handled this correctly. But this didn't cause any problems till
> > now as KVM_PPC_ALLOCATE_HTAB ioctl returned with smaller than requested
> > HTAB when enough contiguous memory wasn't available in the host.
> > After the proposed kernel change: 
> > https://patchwork.ozlabs.org/patch/530501/,
> > KVM_PPC_ALLOCATE_HTAB ioctl will not fallback to lower sized HTAB
> > allocation and will fail if requested HTAB size can't be met.
> > 
> > Check for such failures in QEMU and abort appropriately. This will
> > prevent guest kernel from hanging/freezing during early boot by doing
> > graceful exit when host is unable to allocate requested HTAB.
> > 
> > Signed-off-by: Bharata B Rao <address@hidden>
> 
> I'm going to apply this, since it fixes a real problem.
> 
> I'm not entirely happy with the way it's done though - I'd prefer to
> see a separate case for (shift < 0) giving an unconditional error.
> Handling both the HV success case and the failure case in that first
> branch is unnecessarily subtle and confusing, IMO.

Ugh.. actually.. this patch seems to cause make check failures when
configured for powerpc guest on an x86 host.  I haven't debugged yet,
but I'm guessing the shift != 0 is now catching the TCG (or PR) case
where we need to allocate the htab ourselves.

> 
> 
> > ---
> >  hw/ppc/spapr.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index e1202ce..ec6e141 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -1022,7 +1022,7 @@ static void spapr_alloc_htab(sPAPRMachineState *spapr)
> >  
> >      shift = kvmppc_reset_htab(spapr->htab_shift);
> >  
> > -    if (shift > 0) {
> > +    if (shift != 0) {
> >          /* Kernel handles htab, we don't need to allocate one */
> >          if (shift != spapr->htab_shift) {
> >              error_setg(&error_abort, "Failed to allocate HTAB of requested 
> > size, try with smaller maxmem");
> > @@ -1055,7 +1055,7 @@ static void spapr_reset_htab(sPAPRMachineState *spapr)
> >      int index;
> >  
> >      shift = kvmppc_reset_htab(spapr->htab_shift);
> > -    if (shift > 0) {
> > +    if (shift != 0) {
> >          if (shift != spapr->htab_shift) {
> >              error_setg(&error_abort, "Requested HTAB allocation failed 
> > during reset");
> >          }
> 



-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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