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Commit 8f21a0bb authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
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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: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent f3bbc0dc

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);