kvm tools: Add memory gap for larger RAM sizes

kvm tools: Add memory gap for larger RAM sizes

e820 is expected to leave a memory gap within the low 32
bits of RAM space. From the documentation of e820_setup_gap():

  /*
   * Search for the biggest gap in the low 32 bits of the e820
   * memory space.  We pass this space to PCI to assign MMIO resources
   * for hotplug or unconfigured devices in.
   * Hopefully the BIOS let enough space left.
   */

Not leaving such gap causes errors and hangs during the boot process.

This patch adds a memory gap between 0xe0000000 and 0x100000000 when using more
than 0xe0000000 bytes for guest RAM.

This patch updates the e820 table, slot allocations used for
KVM_SET_USER_MEMORY_REGION.

Acked-and-tested-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>