[PATCH v2 07/26] KVM: VMX: Relax check on unusable segment

Avi Kivity
2012-06-27T15:19:51Z

Some userspace (e.g. QEMU 1.1) munge the d and g bits of segment
descriptors, causing us not to recognize them as unusable segments
with emulate_invalid_guest_state=1. Relax the check by testing for
segment not present (a non-present segment cannot be usable).

Signed-off-by: Avi Kivity <avi@redhat.com>
---
arch/x86/kvm/vmx.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 8f2ddd9..a9c0e40 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3198,7 +3198,7 @@ static u32 vmx_segment_access_rights(struct kvm_segment *var)
{
u32 ar;

- if (var->unusable)
+ if (var->unusable || !var->present)
ar = 1 << 16;
else {
ar = var->type & 15;
@@ -3210,8 +3210,6 @@ static u32 vmx_segment_access_rights(struct kvm_segment *var)
ar |= (var->db & 1) << 14;
ar |= (var->g & 1) << 15;
}
- if (ar == 0) /* a 0 value means unusable */
- ar = AR_UNUSABLE_MASK;

return ar;
}
--
1.7.11