Commit c0c7c04b authored Aug 11, 2009 by Anthony Liguori Committed by Avi Kivity Sep 10, 2009

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: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Avi 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;

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