Re: [Qemu-devel] [PATCH v1 2/2] spapr: Handle failure of KVM_PPC_ALLOCATE_HTAB ioctl

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Nov 10, 2015 at 08:38:57AM -0600, Michael Roth wrote:
> Quoting Bharata B Rao (2015-11-09 23:24:54)
> > 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 <bharata@linux.vnet.ibm.com>
> > ---
> >  hw/ppc/spapr.c | 20 ++++++++++++++++----
> >  1 file changed, 16 insertions(+), 4 deletions(-)
> > 
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index e1202ce..a64a1b5 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -1021,9 +1021,19 @@ static void spapr_alloc_htab(sPAPRMachineState *spapr)
> >       * RAM */
> > 
> >      shift = kvmppc_reset_htab(spapr->htab_shift);
> > -
> > -    if (shift > 0) {
> > -        /* Kernel handles htab, we don't need to allocate one */
> > +    if (shift < 0) {
> > +        /*
> > +         * For HV KVM, host kernel will return -ENOMEM when requested
> > +         * HTAB size can't be allocated.
> > +         */
> > +        error_setg(&error_abort, "Failed to allocate HTAB of requested size, try with smaller maxmem");
> 
> Wording is appropriate, but maybe just "Failed to allocate HTAB, try with
> smaller maxmem" to distinguish it from the error below where the call succeeds
> but there's a size mismatch?

Possibly the message could be a little better, but I'm not going to
hold up the patches just for that.  I've applied tentatively to
spapr-next, and I hope to send a pull req with it soon, assuming it
survives my tests.

-- 
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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