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KVM: vmx: skip VMWRITE of HOST_{FS,GS}_SEL when possible

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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>
This commit is contained in:
Sean Christopherson 2018-07-23 12:32:49 -07:00 committed by Paolo Bonzini
parent f3bbc0dced
commit 8f21a0bbf3
1 changed files with 14 additions and 10 deletions
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24
arch/x86/kvm/vmx.c
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@ -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);