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>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 265fdd37b240..7c2c05406b60 100644
--- 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))