On a 64-bit host, FS.sel and GS.sel are all but guaranteed to be 0,
which in turn means they'll rarely change. Skip the VMWRITE for the
associated VMCS fields when loading host state if the selector hasn't
changed since the last VMWRITE.
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
arch/x86/kvm/vmx.c | 24 ++++++++++++++----------
1 file changed, 14 insertions(+), 10 deletions(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index b24cd74c905c..9f3bd199dc8c 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2619,16 +2619,20 @@ static void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
gs_base = segment_base(gs_sel);
#endif
- host_state->fs_sel = fs_sel;
- if (!(fs_sel & 7))
- vmcs_write16(HOST_FS_SELECTOR, fs_sel);
- else
- vmcs_write16(HOST_FS_SELECTOR, 0);
- host_state->gs_sel = gs_sel;
- if (!(gs_sel & 7))
- vmcs_write16(HOST_GS_SELECTOR, gs_sel);
- else
- vmcs_write16(HOST_GS_SELECTOR, 0);
+ if (unlikely(fs_sel != host_state->fs_sel)) {
+ if (!(fs_sel & 7))
+ vmcs_write16(HOST_FS_SELECTOR, fs_sel);
+ else
+ vmcs_write16(HOST_FS_SELECTOR, 0);
+ host_state->fs_sel = fs_sel;
+ }
+ if (unlikely(gs_sel != host_state->gs_sel)) {
+ if (!(gs_sel & 7))
+ vmcs_write16(HOST_GS_SELECTOR, gs_sel);
+ else
+ vmcs_write16(HOST_GS_SELECTOR, 0);
+ host_state->gs_sel = gs_sel;
+ }
vmcs_writel(HOST_FS_BASE, fs_base);
vmcs_writel(HOST_GS_BASE, gs_base);
--
2.18.0
