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@xxxxxxxxxx>
---
v1 -> v2 Simplify by folding check into kvm_load_segment_descriptor()
---
arch/x86/kvm/x86.c | 9 ++++++++-
1 files changed, 8 insertions(+), 1 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6263991..f9c9f85 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4007,12 +4007,19 @@ 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;
--
1.6.2.5
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