[PATCH 2/2] KVM: VMX: Optimize atomic EFER load

Avi Kivity
2010-12-21T10:54:35Z

When NX is enabled on the host but not on the guest, we use the entry/exit
msr load facility, which is slow. Optimize it to use entry/exit efer load,
which is ~1200 cycles faster.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
arch/x86/kvm/vmx.c | 30 ++++++++++++++++++++++++++++++
1 files changed, 30 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index c195260..b997fdb 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -191,6 +191,8 @@ static unsigned long *vmx_io_bitmap_b;
static unsigned long *vmx_msr_bitmap_legacy;
static unsigned long *vmx_msr_bitmap_longmode;

+static bool cpu_has_load_ia32_efer;
+
static DECLARE_BITMAP(vmx_vpid_bitmap, VMX_NR_VPIDS);
static DEFINE_SPINLOCK(vmx_vpid_lock);

@@ -664,6 +666,12 @@ static void clear_atomic_switch_msr(struct vcpu_vmx *vmx, unsigned msr)
unsigned i;
struct msr_autoload *m = &vmx->msr_autoload;

+ if (msr == MSR_EFER && cpu_has_load_ia32_efer) {
+ vmcs_clear_bits(VM_ENTRY_CONTROLS, VM_ENTRY_LOAD_IA32_EFER);
+ vmcs_clear_bits(VM_EXIT_CONTROLS, VM_EXIT_LOAD_IA32_EFER);
+ return;
+ }
+
for (i = 0; i < m->nr; ++i)
if (m->guest[i].index == msr)
break;
@@ -683,6 +691,14 @@ static void add_atomic_switch_msr(struct vcpu_vmx *vmx, unsigned msr,
unsigned i;
struct msr_autoload *m = &vmx->msr_autoload;

+ if (msr == MSR_EFER && cpu_has_load_ia32_efer) {
+ vmcs_write64(GUEST_IA32_EFER, guest_val);
+ vmcs_write64(HOST_IA32_EFER, host_val);
+ vmcs_set_bits(VM_ENTRY_CONTROLS, VM_ENTRY_LOAD_IA32_EFER);
+ vmcs_set_bits(VM_EXIT_CONTROLS, VM_EXIT_LOAD_IA32_EFER);
+ return;
+ }
+
for (i = 0; i < m->nr; ++i)
if (m->guest[i].index == msr)
break;
@@ -1418,6 +1434,14 @@ static __init int adjust_vmx_controls(u32 ctl_min, u32 ctl_opt,
return 0;
}

+static __init bool allow_1_setting(u32 msr, u32 ctl)
+{
+ u32 vmx_msr_low, vmx_msr_high;
+
+ rdmsr(msr, vmx_msr_low, vmx_msr_high);
+ return vmx_msr_high & ctl;
+}
+
static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
{
u32 vmx_msr_low, vmx_msr_high;
@@ -1532,6 +1556,12 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
vmcs_conf->vmexit_ctrl = _vmexit_control;
vmcs_conf->vmentry_ctrl = _vmentry_control;

+ cpu_has_load_ia32_efer =
+ allow_1_setting(MSR_IA32_VMX_ENTRY_CTLS,
+ VM_ENTRY_LOAD_IA32_EFER)
+ && allow_1_setting(MSR_IA32_VMX_EXIT_CTLS,
+ VM_EXIT_LOAD_IA32_EFER);
+
return 0;
}

--
1.7.1