KVM: vmx: skip VMWRITE of HOST_{FS,GS}_SEL when possible (8f21a0bb) · Commits · 戴 / test

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@intel.com> Signed-off-by:

Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx.c

+14 −10

Original line number	Diff line number	Diff line
		@@ -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 (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->gs_sel = gs_sel;
		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);

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