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KVM: When switching to a vm8086 task, load segments as 16-bit

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According to 16.2.5 in the SDM, eflags.vm in the tss is consulted before loading
and new segments.  If eflags.vm == 1, then the segments are treated as 16-bit
segments.  The LDTR and TR are not normally available in vm86 mode so if they
happen to somehow get loaded, they need to be treated as 32-bit segments.

This fixes an invalid vmentry failure in a custom OS that was happening after
a task switch into vm8086 mode.  Since the segments were being mistakenly
treated as 32-bit, we loaded garbage state.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Anthony Liguori 2009-08-11 15:57:59 -05:00 committed by Avi Kivity
parent 345dcaa8fd
commit c0c7c04b87
1 changed files with 8 additions and 1 deletions
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9
arch/x86/kvm/x86.c
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@ -4101,12 +4101,19 @@ static int kvm_load_realmode_segment(struct kvm_vcpu *vcpu, u16 selector, int se
return 0;
}
static int is_vm86_segment(struct kvm_vcpu *vcpu, int seg)
{
return (seg != VCPU_SREG_LDTR) &&
(seg != VCPU_SREG_TR) &&
(kvm_x86_ops->get_rflags(vcpu) & X86_EFLAGS_VM);
}
int kvm_load_segment_descriptor(struct kvm_vcpu *vcpu, u16 selector,
int type_bits, int seg)
{
struct kvm_segment kvm_seg;
if (!(vcpu->arch.cr0 & X86_CR0_PE))
if (is_vm86_segment(vcpu, seg) || !(vcpu->arch.cr0 & X86_CR0_PE))
return kvm_load_realmode_segment(vcpu, selector, seg);
if (load_segment_descriptor_to_kvm_desct(vcpu, selector, &kvm_seg))
return 1;