From 4311c21d91d38d3b5feb97be972731df66c1d650 Mon Sep 17 00:00:00 2001 From: Pekka Enberg Date: Sat, 27 Mar 2010 11:15:31 +0200 Subject: [PATCH] kvm: Document the 'reset vector' hack Signed-off-by: Pekka Enberg --- kvm.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/kvm.c b/kvm.c index e922b93..b7ec6e6 100644 --- a/kvm.c +++ b/kvm.c @@ -153,6 +153,13 @@ static inline uint32_t segment_to_flat(uint16_t selector, uint16_t offset) return ((uint32_t)selector << 4) + (uint32_t) offset; } +/* + * HACK ALERT! KVM seems to be unable to run 16-bit real mode if 'cs' selector + * does not equal to 0xf000 at the beginning. To work around that, we need a + * 'reset vector' at 0xf000:0xfff0 that has an hard-coded jump to 0x000:0x7c000 + * where we also load the Linux kernel boot sector and setup code. + */ + #define RESET_VECTOR_CS 0xf000 #define RESET_VECTOR_IP 0xfff0