[Qemu-devel] [RFC PATCH v0 0/2] spapr: Abort when HTAB size requirement can't be met

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

HTAB size is a factor of maximum memory size that is specified by maxmem=
command line option. In cases where there is shortage of host memory, host
will not be able to allocate contiguous memory for guest HTAB and will
instead allocate a smaller HTAB. This usually is not a problem but when
user starts hotplugging memory to the guest, we can run out of HTAB entries
and hence memory hotplug fails. This failure should have been handled
gracefully by the guest kernel, but currently it leads to guest kernel OOPS.
This will eventually get fixed when the handling of memory hotplug is
completely moved to kernel for PowerKVM.

Prevent such kernel failure by refusing to boot the guest when requested
HTAB size can't be allocated. However HTAB allocation happens in the
reset path from where it is too late to abort. Hence this patchset
moves the HTAB allocation to machine init and aborts if HTAB size
requirement isn't met.

Two previous related attempts to address this problem:

1. http://lists.nongnu.org/archive/html/qemu-devel/2015-07/msg03325.html
   Aborts the guest from the reset path - not desirable.
2. https://lists.gnu.org/archive/html/qemu-devel/2015-08/msg02602.html
   Silently disables memory hotplug - not desirable.

This patchset applies against David Gibson's spapr-next.

Bharata B Rao (2):
  spapr: Allocate HTAB from machine init
  spapr: Abort when HTAB of requested size isn't allocated

 hw/ppc/spapr.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

-- 
2.1.0