smm: Backup and restore A20 on an SMI based mode switch

QEMU does not store the A20 setting in the SMM cpu environment area
(and it does not look like real CPUs do either).  So, manually backup
and restore A20 on a mode switch.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
1 file changed
tree: 4c5819a7af68e88e75a725f211142cf4e900271c
  1. .gitignore
  2. COPYING
  3. COPYING.LESSER
  4. Makefile
  5. README
  6. docs/
  7. scripts/
  8. src/
  9. vgasrc/