From 5e079c7ece1060491ef4a45414823162cce91b3d Mon Sep 17 00:00:00 2001
From: Sean Christopherson <sean.j.christopherson@intel.com>
Date: Mon, 23 Jul 2018 12:32:50 -0700
Subject: [PATCH] KVM: vmx: skip VMWRITE of HOST_{FS,GS}_BASE when possible
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>
---
arch/x86/kvm/vmx.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 4937e11f971a7..b23ecc04ca512 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -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,
--
GitLab