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.
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>
---
arch/x86/kvm/x86.c | 23 +++++++++++++++++------
1 files changed, 17 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6263991..48b1be9 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4050,6 +4050,16 @@ static void save_state_to_tss32(struct kvm_vcpu *vcpu,
tss->ldt_selector = get_segment_selector(vcpu, VCPU_SREG_LDTR);
}
+static int load_seg_from_tss32(struct kvm_vcpu *vcpu,
+ struct tss_segment_32 *tss,
+ u16 selector, int type_bits, int seg)
+{
+ if ((tss->eflags & X86_EFLAGS_VM))
+ return kvm_load_realmode_segment(vcpu, selector, seg);
+
+ return kvm_load_segment_descriptor(vcpu, selector, type_bits, seg);
+}
+
static int load_state_from_tss32(struct kvm_vcpu *vcpu,
struct tss_segment_32 *tss)
{
@@ -4070,23 +4080,24 @@ static int load_state_from_tss32(struct kvm_vcpu *vcpu,
if (kvm_load_segment_descriptor(vcpu, tss->ldt_selector, 0, VCPU_SREG_LDTR))
return 1;
- if (kvm_load_segment_descriptor(vcpu, tss->es, 1, VCPU_SREG_ES))
+ if (load_seg_from_tss32(vcpu, tss, tss->es, 1, VCPU_SREG_ES))
return 1;
- if (kvm_load_segment_descriptor(vcpu, tss->cs, 9, VCPU_SREG_CS))
+ if (load_seg_from_tss32(vcpu, tss, tss->cs, 9, VCPU_SREG_CS))
return 1;
- if (kvm_load_segment_descriptor(vcpu, tss->ss, 1, VCPU_SREG_SS))
+ if (load_seg_from_tss32(vcpu, tss, tss->ss, 1, VCPU_SREG_SS))
return 1;
- if (kvm_load_segment_descriptor(vcpu, tss->ds, 1, VCPU_SREG_DS))
+ if (load_seg_from_tss32(vcpu, tss, tss->ds, 1, VCPU_SREG_DS))
return 1;
- if (kvm_load_segment_descriptor(vcpu, tss->fs, 1, VCPU_SREG_FS))
+ if (load_seg_from_tss32(vcpu, tss, tss->fs, 1, VCPU_SREG_FS))
return 1;
- if (kvm_load_segment_descriptor(vcpu, tss->gs, 1, VCPU_SREG_GS))
+ if (load_seg_from_tss32(vcpu, tss, tss->gs, 1, VCPU_SREG_GS))
return 1;
+
return 0;
}
--
1.6.2.5
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
