KVM: VMX: relax check for CS register in rmode_segment_valid()

rmode_segment_valid() checks if segment descriptor can be used to enter
vm86 mode. VMX spec mandates that in vm86 mode CS register will be of
type data, not code. Lets allow guest entry with vm86 mode if the only
problem with CS register is incorrect type. Otherwise entire real mode
will be emulated.

Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 265fdd37b24020675fdbc5d59966a6149f9bc37f..7c2c05406b601f2267c1564d0b2ae598efde1bb4 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3383,6 +3383,8 @@ static bool rmode_segment_valid(struct kvm_vcpu *vcpu, int seg)
        var.dpl = 0x3;
        var.g = 0;
        var.db = 0;
+       if (seg == VCPU_SREG_CS)
+               var.type = 0x3;
        ar = vmx_segment_access_rights(&var);
 
        if (var.base != (var.selector << 4))