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

[Michael Roth <mdroth@linux.vnet.ibm.com>]

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?

> +    } else if (shift > 0) {
> +        /*
> +         * Kernel handles htab, we don't need to allocate one
> +         *
> +         * Older kernels can fall back to lower HTAB shift values,
> +         * but we don't allow booting of such guests.
> +         */
>          if (shift != spapr->htab_shift) {
>              error_setg(&error_abort, "Failed to allocate HTAB of requested size, try with smaller maxmem");
>          }
> @@ -1055,7 +1065,9 @@ static void spapr_reset_htab(sPAPRMachineState *spapr)
>      int index;
> 
>      shift = kvmppc_reset_htab(spapr->htab_shift);
> -    if (shift > 0) {
> +    if (shift < 0) {
> +        error_setg(&error_abort, "Failed to reset HTAB");
> +    } else if (shift > 0) {
>          if (shift != spapr->htab_shift) {
>              error_setg(&error_abort, "Requested HTAB allocation failed during reset");
>          }
> -- 
> 2.1.0
>