From 8f21a0bbf36f58334695ae6e46c0cf906a217154 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Mon, 23 Jul 2018 12:32:49 -0700 Subject: [PATCH] KVM: vmx: skip VMWRITE of HOST_{FS,GS}_SEL when possible 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 Signed-off-by: Paolo Bonzini --- 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 60bf9a9..4937e11 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -2717,16 +2717,20 @@ 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); -- 2.7.4