Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit c0c7c04b authored by Anthony Liguori's avatar Anthony Liguori Committed by Avi Kivity
Browse files

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



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: default avatarAnthony Liguori <aliguori@us.ibm.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent 345dcaa8

arch/x86/kvm/x86.c

+8 −1
Original line number Diff line number Diff line
@@ -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;