KVM: x86 emulator: add get_cached_segment_base() callback to x86_emulate_ops

On VMX it is expensive to call get_cached_descriptor() just to get segment
base since multiple vmcs_reads are done instead of only one. Introduce
new call back get_cached_segment_base() for efficiency.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e3a5455049b..9a469df6011 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3714,6 +3714,12 @@ static void emulator_get_gdt(struct desc_ptr *dt, struct kvm_vcpu *vcpu)
         kvm_x86_ops->get_gdt(vcpu, dt);
 }
 
+static unsigned long emulator_get_cached_segment_base(int seg,
+                                                      struct kvm_vcpu *vcpu)
+{
+        return get_segment_base(vcpu, seg);
+}
+
 static bool emulator_get_cached_descriptor(struct desc_struct *desc, int seg,
                                            struct kvm_vcpu *vcpu)
 {
@@ -3804,6 +3810,7 @@ static struct x86_emulate_ops emulate_ops = {
         .set_cached_descriptor = emulator_set_cached_descriptor,
         .get_segment_selector = emulator_get_segment_selector,
         .set_segment_selector = emulator_set_segment_selector,
+        .get_cached_segment_base = emulator_get_cached_segment_base,
         .get_gdt             = emulator_get_gdt,
         .get_cr              = emulator_get_cr,
         .set_cr              = emulator_set_cr,