kvm: Remove 'reset vector' hack

As explained by Avi Kivity, KVM on Intel requires segment 'base' to equal to
'selector * 16'.  Fix that up and remove the 'reset vector' hack.

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

diff --git a/tools/kvm/kvm.c b/tools/kvm/kvm.c
index af13a31208277716eb38f8f528cede39db7bfe0e..4214675107913e5021fb010a0c28bceacef5c4d3 100644 (file)
--- a/tools/kvm/kvm.c
+++ b/tools/kvm/kvm.c
@@ -153,27 +153,6 @@ 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
-
-static unsigned char reset_vector_code[] = { 0xea, 0x00, 0x7c, 0x00, 0x00 };
-
-static void load_reset_vector(struct kvm *self)
-{
-       void *p;
-
-       p       = guest_addr_to_host(self, segment_to_flat(RESET_VECTOR_CS, RESET_VECTOR_IP));
-
-       memcpy(p, reset_vector_code, ARRAY_SIZE(reset_vector_code));
-}
-
 #define BOOT_LOADER_CS         0x0000
 #define BOOT_LOADER_IP         0x7c00
 
@@ -284,13 +263,15 @@ static inline uint64_t ip_real_to_flat(struct kvm *self, uint64_t ip)
 
 void kvm__reset_vcpu(struct kvm *self)
 {
-       load_reset_vector(self);
-
        self->sregs = (struct kvm_sregs) {
                .cr0            = 0x60000010ULL,
                .cs             = (struct kvm_segment) {
-                       .selector       = RESET_VECTOR_CS,
-                       .base           = 0xffff0000UL,
+                       /*
+                        * KVM on Intel requires 'base' to be 'selector * 16' in
+                        * real mode.
+                        */
+                       .selector       = BOOT_LOADER_CS,
+                       .base           = BOOT_LOADER_CS * 16,
                        .limit          = 0xffffU,
                        .type           = 0x0bU,
                        .present        = 1,
@@ -354,7 +335,7 @@ void kvm__reset_vcpu(struct kvm *self)
                die_perror("KVM_SET_SREGS failed");
 
        self->regs = (struct kvm_regs) {
-               .rip            = RESET_VECTOR_IP,
+               .rip            = BOOT_LOADER_IP,
                /* We start the guest in 16-bit real mode  */
                .rflags         = 0x0000000000000002ULL,
        };