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

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The host's FS.base and GS.base rarely change, e.g. ~0.1% of host/guest
swaps on my system.  Cache the last value written to the VMCS and skip
the VMWRITE to the associated VMCS fields when loading host state if
the value 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 12:32:50 -07:00 committed by Paolo Bonzini
parent 8f21a0bbf3
commit 5e079c7ece
1 changed files with 10 additions and 3 deletions
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13
arch/x86/kvm/vmx.c
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@ -226,6 +226,8 @@ struct vmcs {
struct vmcs_host_state {
unsigned long cr3; /* May not match real cr3 */
unsigned long cr4; /* May not match real cr4 */
unsigned long gs_base;
unsigned long fs_base;
u16 fs_sel, gs_sel, ldt_sel;
#ifdef CONFIG_X86_64
@ -2731,9 +2733,14 @@ static void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
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);
if (unlikely(fs_base != host_state->fs_base)) {
vmcs_writel(HOST_FS_BASE, fs_base);
host_state->fs_base = fs_base;
}
if (unlikely(gs_base != host_state->gs_base)) {
vmcs_writel(HOST_GS_BASE, gs_base);
host_state->gs_base = gs_base;
}
for (i = 0; i < vmx->save_nmsrs; ++i)
kvm_set_shared_msr(vmx->guest_msrs[i].index,